Background and Summary of a Guide for Roundabouts (2023)

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73 Appendix C: Synthesis Summaries 1. DESIGNING FOR OVERSIZED/OVERWEIGHT TRUCKS SYNTHESIS SUMMARY This synthesis describes how roundabouts can address various truck capabilities and how Oversize/Overweight highway trucks (OSOWs) can be accommodated via horizontal, vertical, and cross- section design. Oversize/Overweight highway truck (OSOW) accommodations affect pavement structure, roadway geometrics, and traffic operations. Because of the variety of OSOWs and the routes they may take, OSOW accommodations are best determined on a case-by-case basis with appropriate stakeholders involved. STATE OF THE PRACTICE REVIEW The state of the practice review summarizes the findings and policies from the following documents: • NCHRP Report 672, Roundabouts: An Informational Guide, Second Edition (Rodegerdts et al. 2010) • Accommodating Oversize/Overweight Vehicles at Roundabouts (Russell et al. 2013) NCHRP Report 672, Roundabouts: An Informational Guide, Second Edition NCHRP Report 672, Roundabouts: An Informational Guide, Second Edition (NCHRP Report 672) provides guidance related to accommodating OSOWs at roundabouts. According to NCHRP Report 672, roundabouts may need accommodations for OSOWs in rural areas and manufacturing areas as well as at larger statewide freeway interchanges and intersections with statewide highways. NCHRP Report 672 states that a larger footprint and larger inscribed circle diameter are often used to “accommodate large vehicles while maintaining low speeds for passenger vehicles.” NCHRP Report 672 generally advises against designing a roundabout to provide “normal circulation” for OSOWs, as this may result in “excessive dimensions and higher speeds for the majority of users.” NCHRP Report 672 recommends engaging local stakeholders to develop proper accommodations and notes that for OSOWs, “it may be appropriate to choose another route entirely, negating the need to design the roundabout to accommodate these vehicles.” (Rodegerdts et al. 2010) Accommodating Oversize/Overweight Vehicles at Roundabouts (Report No. KSU- 10-1) The authors found that OSOWs should be accommodated for traffic operations, roadway geometrics, and pavement structure. The report was not intended to be a design guide; however, it contains design considerations. The authors recommended states develop a freight network, including segments where OSOW accommodations are needed, based on “state and federal commerce laws and policies and the state’s economy.” The vehicles to be accommodated should represent materials critical to the economy of the state. The authors note Wisconsin has developed a good example of an OSOW network. Stakeholders

74 should be considered when determining the proper design vehicle at a given location, such as nearby shippers, carriers, terminal operators, economic development agencies, seaport and airport authorities, state and local governments, stores, distribution centers, warehouse representatives, and commercial and industrial developers. One of the surveys found that states should reconsider laws that “make large trucks liable for damages in a crash just for being out of their lane,” as this may be necessary for large trucks to navigate the roundabout. The research identified that vertical ground clearance for vertical elements of a roundabout is a “major problem” for OSOWs. The authors recommended that roundabouts needing to accommodate OSOWs be designed with a maximum height of 3 in for splitter islands, truck aprons, and curbs. Although the document does not serve as a design guide, the authors provided ideas and concepts for examples of OSOW accommodations based on the surveys and their literature review. These include: • Constructing truck aprons at least 12 ft wide with minimum slope and mountable curb. • Constructing custom center islands out of pavement and stabilized turf to accommodate OSOW movements. The shape of the center island may be adjusted to accommodate off-tracking or through movements. • Providing sufficient clear areas in the center island, which may be achieved by using signs and features that can be easily removed to accommodate OSOWs. • Providing a straight passage through the center island. This passage may be gated, and the entrance should line up with the left lane of the roundabout. • Providing a right-turn slip lane to accommodate right-turning movements. • Allowing OSOWs to travel contraflow. The research found the clearance area needed to accommodate OSOWs can usually be decreased if left turns can be accommodated in the opposite direction of travel. • Designing the median so that OSOWs may cross over the median before the splitter island to start the turn. • Using laying mats or other temporary methods to protect the roundabout from potential damage when OSOWs are expected to travel off-track. (Russell et al. 2013) Key Findings Agencies should conduct a survey to develop a freight network that includes the segments and turning movements where OSOW accommodations are needed. Stakeholders should also be considered when determining proper accommodations for OSOWs. These accommodations include vertical ground clearance, sufficient clear areas, permitting atypical vehicle movements (such as contra-flow), and temporary methods that protect the roundabout from off-tracking (Russell, et al., 2013). TRANSPORTATION AGENCY OUTREACH Kansas Department of Transportation (KDOT) Conversations with KDOT noted that they did not have any roundabout codes, statutes, or laws to provide for OSOW accommodation at roundabouts. They use the Kansas Roundabout Guide, Second Edition and K-TRAN report, Accommodating Oversize/Overweight Vehicles at Roundabouts (KDOT 2014; Russell et al. 2013).

75 KDOT reviews intersections where a roundabout is proposed and determines the appropriate design vehicle for that location. KDOT verifies design vehicles when a roundabout is proposed on routes designated as freight corridors. KDOT published the Kansas Roundabout Guide, Second Edition in 2014. The primary concerns mentioned in the guide include “length, width, ground clearance of the load, and the swept path of the vehicle and load.” The guide recommends OSOW accommodations on a case-by-case basis, provides potential OSOW design modifications, and refers readers to NCHRP Report 672 for further guidance (KDOT 2014). The K-TRAN report, KSU-10-1: Accommodating Oversize/Overweight Vehicles at Roundabouts, is included in the “State of The Practice Review” section of this report (Russell et al. 2013). Wisconsin Department of Transportation (WisDOT) Conversations with WisDOT revealed guidance on OSOW accommodation and WisDOT-specific legislation for considering OSOW at roundabouts. WisDOT developed a network map of OSOW routes and a library of OSOW for use in AutoTURN to design roundabouts along those routes. Sections 11-26.10.2.3 and 11-26.30.5.6 of the WisDOT Facilities Development Manual (FDM) describe OSOW design procedures. These sections provide guidance on determining an OSOW route, considering a review of permits to determine which vehicles have a history of using the intersection, and performing vertical checks to ensure the relevant OSOWs can clear necessary vertical elements of the roundabout (WisDOT 2016). Conversations with WisDOT noted that if there is adequate communication with area stakeholders and OSOW haulers, then locations are not typically excluded from roundabout use due to OSOW requirements. The general process of accommodating OSOWs for WisDOT includes: first, design the roundabout without considering OSOWs to suit the primary safety and operations focus of the roundabout. Then, modify the roundabout with over-tracking pads or other modifications that do not impact the daily operation of the roundabout. Oregon Department of Transportation (ODOT) Conversations with ODOT revealed guidance on ODOT-specific guidance and legislation for OSOW accommodation at roundabouts. Or. Rev. Stat. § 366.215 (2003)), Or. Rev. Stat. § 811.292 (2022), Oregon Administrative Rule (OAR) § 731-012, and the Oregon Highway Division Directive (DES-02) were discussed (State of Oregon, 2003; State of Oregon 2022; ODOT 2013; ODOT 2017). These ORS policies have the following impacts on roundabout design and operations: • The design “may not permanently reduce the vehicle-carrying capacity” in terms of “horizontal or vertical clearance of a highway section” of an identified freight route “unless safety or access considerations require the reduction.” o Roundabouts proposed on the state highway system shall not impede OSOW movement. • Designated statewide representatives of the trucking industry will create a documented agreement before construction of a roundabout on the state highway system stating that the roundabout incorporates the proper design vehicle and can appropriately accommodate OSOWs. • Passing or driving beside a commercial vehicle in a roundabout is a Class C Traffic Violation.

76 o This seeks to address safety concerns associated with sideswipe and overtaking crashes between trucks and passenger vehicles. Conversations with ODOT noted that roundabout-specific communication with the trucking industry is necessary on a case-by-case basis for decision elements, such as route mobility, design vehicle exceptions, OSOWs to be accommodated, and typical design elements for any proposed roundabout on the state highway system. Washington State Department of Transportation (WSDOT) Conversations with WSDOT revealed that WSDOT does not have roundabout policies, statutes, or codes to provide for OSOW accommodation. California Department of Transportation (Caltrans) Conversations with Caltrans noted that current design guidance does not specifically address OSOWs when discussing design vehicles or roundabout accommodations. Summary The research team reviewed current planning and design information, including published design guidelines, statutes, laws, codes, and policies related to the effect OSOWs have on roundabouts for: • Florida Department of Transportation (FDOT) • Georgia Department of Transportation (GDOT) • Maryland State Highway Authority (MDOT SHA) • Massachusetts Department of Transportation (MassDOT) • North Carolina Department of Transportation (NCDOT) A summary of the findings for the states reviewed is presented in Table 1 below.

77 Table 1. State Guidance for OSOW Accommodations at Roundabouts State Published Guidance General Comment California None Caltrans is in the process of updating guidance on OSOWs. These updates may relate to roundabout design elements, design vehicles, and determination of routes requiring accommodations based on existing permits and the presence of alternative routes. Florida None OSOW accommodation at roundabouts is site-specific and includes an understanding of the specific turning movements required for the vehicle. Georgia GDOT Roundabout Design Guide (GDOT 2019) Contacts mentioned that OSOW accommodation operates based on knowledge of current practices in other states rather than from codes. They consider permits when selecting a design vehicle. The design guide includes documentation of OSOWs during Stage 2 of an intersection control evaluation. Once a roundabout is programmed for construction, “OSOW single-trip permits should be requested to determine and analyze the check vehicle on the roundabout design.” Kansas KDOT Kansas Roundabout Guide, Second Edition (KDOT 2014) Our contact stated that KDOT reviews intersections where a roundabout is proposed and determines the appropriate “design vehicle” for that location. KDOT “pays particular attention” when a roundabout is proposed on “routes designated as freight corridors.” Contact referred to the Kansas Roundabout Guide, which recommends OSOW accommodations on a case-by-case basis. The primary concerns mentioned in the guide include “length, width, ground clearance of the load, and the swept path of the vehicle and load” (KDOT 2014). Maryland None Contacts provided no formal state guidance on OSOW accommodation in roundabouts but stated that concerns relate to vertical clearance, objects in the center island, and the route and movements OSOWs take. Massachusetts None Our contact stated that OSOWs have not needed accommodations at any roundabouts in his district. North Carolina None OSOW considerations are determined on a case-by-case basis. Oregon Or. Rev. Stat. § 366.215 (2003); Oregon Administrative Rule (OAR) 731-012; Or. Rev. Stat. § 811.292; OAR 731- 012, Highway Division Directive DES-02 Roundabouts may not permanently reduce capacity along a freight route unless required by safety or access problems. A documented agreement by designated statewide representatives is needed before the construction of a roundabout on the state highway system stating that the roundabout incorporates the proper design vehicle and can appropriately accommodate OSOWs. Washington None Contacts provided no formal or informal guidance related to OSOWs. Wisconsin WisDOT Facilities Development Manual (FDM) Sections 11-26.10.2.3 and 11- 26.30.5.6 (WisDOT 2016) WisDOT FDM provides guidance on determining an OSOW route and on conducting vertical checks to ensure the relevant OSOWs can clear necessary vertical elements of the roundabout (WisDOT 2016).

78 Key Findings Generally, states do not have substantial published guidance for OSOW accommodation at roundabouts. In practice, states evaluate accommodations on a case-by-case basis. Conversations with state agencies revealed that if there is adequate communication with area stakeholders and OSOW haulers, roundabout locations are typically not excluded due to OSOW requirements. This communication includes elements like route mobility, design vehicle exceptions, over-dimension vehicle to be accommodated, and typical design elements for any proposed roundabout on the state highway system.

79 2. Economic Impacts of Roundabouts Synthesis Summary This synthesis summarizes information about roundabouts’ economic impacts on businesses, including documents and anecdotal information from jurisdictions that have implemented and invested in roundabouts on commercial corridors. This synthesis considers economic factors for their potential to augment other roundabout performance metrics, such as safety, operational performance, construction cost, and long-term maintenance. The impacts roundabouts can have on businesses and local economies is not well documented and is difficult to objectively evaluate. This synthesis summarizes information related to the business impacts of roundabouts. STATE OF THE PRACTICE REVIEW The state of the practice review summarizes the findings and policies from the following documents: • A Study of the Impact of Roundabouts on Traffic Flows and Business by the Kansas State University Transportation Center (Russell et al. 2012). • Information gathered through jurisdictional outreach. These documents and information are described in the following sections. A Study of the Impact of Roundabouts on Traffic Flows and Business A Study of the Impact of Roundabouts on Traffic Flows and Business studies the impact roundabouts have on surrounding business (Russell et al. 2012). The study looks at roundabouts in Topeka, Kansas, and uses surveys along with simulated before-and-after studies to determine the economic impact of roundabouts. The authors conclude that roundabouts have a positive impact on traffic flows and business. The study operated under the theory that improved traffic flow, access, and safety are either neutral or advantageous for businesses. During a simulated before-and-after study looking at a signalized commercial corridor in Topeka, the after condition investigated traffic flow with all signals replaced by roundabouts. The simulation found reduced stopping, queuing, and delay when using roundabouts in place of signals along the corridor. The study included a survey of businesses in Topeka as well as in Junction City, Kansas; Newton, Kansas; and Carmel, Indiana, to understand the economic impact of roundabouts. Due to a low survey response rate and the presence of other external economic factors, the study found that it was hard to determine if roundabouts, specifically, led to the positive impacts on businesses. The survey reported that businesses in Topeka had a majority favorable view of roundabouts, where 61.5% of participants answered that roundabouts’ impacts were good or very good, and 15.2% of participants said the impacts were bad or very bad. The remaining respondents indicated the impacts were fair. Jurisdiction Outreach Carmel, Indiana Communication with the City of Carmel provided information regarding their experience with roundabouts and businesses. The City noted that development tends to focus along the city’s roundabout corridors. Developers frequently request roundabouts for access to their sites and businesses, such as several businesses along the US 31 Corridor.

80 Communication with the City described an example corridor that demonstrated public feedback regarding the plan for replacing traffic signals with roundabouts. Public comments indicated that the community may not be in favor of the roundabouts because they would limit the ability to “window shop” dealers while queuing at traffic signals. In contrast, congestion at the existing traffic signals was viewed as a deterrent to visit the area. This was expressed in public comments where respondents noted congestion as a reason they avoid the entire area. The City concluded that traffic flow improvements from roundabouts made travel along that corridor more appealing to a wider range of users. Conversations noted that, while construction can be impactful to businesses, there is a significant increase in private development investment along the existing Range Line Road and Carmel Drive corridors (a different roundabout corridor than the previous paragraph). There is also ongoing investment in the City Center portion of the Carmel Drive corridor and additional private development investment along the parallel trail near the Carmel Drive corridor. Pedestrian and bicycle users reported a more comfortable experience along the roundabout corridors. Bird Rock (San Diego), California Bird Rock, a neighborhood in San Diego, had five roundabouts installed along La Jolla Boulevard in 2005 to address high traffic speeds and pedestrian safety. Prior to the roundabout installations, the four-lane roadway had an average vehicular speed of 40 mph and 20,000 vehicles per day, leading to pedestrians feeling unsafe crossing the street. Following the roundabout installations, local businesses had an increase in sales tax receipts for the following years, and vehicular speeds decreased by an average of 41%. Communication with the City revealed that the roundabouts located in their city have half the crashes and a fourth of the injury crashes compared to traffic signals. Reduced congestion and fewer calls allow the police and fire departments to respond faster and reduce pressure for building new stations. Golden, Colorado A roundabout corridor was created along South Golden Road to reduce speeds, improve access to businesses and residential areas, improve safety, and create a more pedestrian friendly environment. After completion, the City documented that the road had reduced 85th percentile speed by 31%, lowered vehicular delay, and eliminated long queues from the adjacent business parking lots (Ariniello 2004). Sales tax was tracked along the corridor and looked at development of nearby businesses in the years surrounding construction. The sales tax revenue increased in subsequent years, and the corridor had approximately $7.6 million in new construction and significant remodeling totals. The City did not track sales tax continuously; however, recent sales tax receipts during the COVID-19 downturn had remained stagnant along this corridor, potentially due to a large grocery store investment. Communication with the City noted that the roundabout corridor is popular amongst the public, with 80% of respondents supporting it. Respondents also indicated the ability to U-turn at roundabouts allowed for easier travel to businesses in the corridor. Bend, Oregon Communication with the City of Bend noted that they did not have information related to the economic impacts of roundabouts on businesses. Clearwater, Florida In Clearwater, Florida, a roundabout was constructed along Clearwater Beach to improve traffic circulation as well as the built environment, which includes tourism and residential, hotel, and retail areas.

81 Communication with those involved with the project noted that the roundabout allows pedestrians to move safely and efficiently to and from the beach and enhances the community character. The economic effect of the adjacent businesses near the roundabout was not tracked, but the roundabout was designed to service approximately 25% more vehicles per hour than the previous sets of intersections it replaced. Key Findings The key findings from the state of the practice review include the following: • Jurisdictions noted that benefits related to safety, operational performance, and construction and maintenance costs were the largest economic factors when considering roundabouts. • Anecdotally, jurisdictions found that reduced delay, stopping, and queuing are key factors in attracting the public and businesses to corridors where they had installed roundabouts. This finding was not directly related to roundabouts versus signals but instead related to the roundabouts providing better traffic operations compared to traffic signals. • Several jurisdictions noted the benefits of bicycle and pedestrian user comfort at roundabouts.

82 3. ILLUMINATION SYNTHESIS SUMMARY This synthesis summarizes recent research findings on roundabout lighting and particularly focuses on ways to increase lighting design flexibility without sacrificing the core safety intent of roadway lighting. The purpose of lighting is twofold: to make the intersection visible from a distance and to make key conflict areas more visible (IES 2018; Rodegerdts et al. 2010). Motor vehicles have headlights and taillights to improve their visibility at night. Vulnerable road users, such as pedestrians and bicyclists, may not have lights or be as visible as vehicles, and unexpected fixed objects or animals may be in travel lanes. Intersection lighting increases visibility. The Illuminating Engineering Society of North America (IES) notes that headlight effectiveness is reduced at roundabouts because of intersection geometry; a driver entering and circulating typically needs to look farther to the left than headlights can track (IES 2018, sec. 12.4.4). As a result, NCHRP Report 672, Roundabouts: An Informational Guide recommends providing lighting at all roundabouts (Rodegerdts et al. 2010). While lighting roundabouts provides visibility and reduces crash risk, it also adds cost and can reduce implementation feasibility. In rural areas, costs of lighting include equipment and installation at the intersection, itself. Further, in cases where no power supply is present within proximity to the site, costs can also include either extending an existing power distribution system to the site or creating a new source (e.g., with a solar array). Lighting operation and maintenance costs typically come from different budgets than the initial capital investment, and these costs may be the responsibility of local agencies or the utility rather than the agency who funded the original capital improvement. Often, solar-powered lighting can reduce the need for an external power supply; however, it may not provide adequate lighting during the winter or in cloudier climates. Understanding where lighting costs can be reduced while minimizing crash risk can increase opportunities to implement roundabouts. STATE OF THE PRACTICE REVIEW The state of the practice review summarizes the findings and policies from the following documents: • NCHRP Report 672, Roundabouts: An Informational Guide, Second Edition (Rodegerdts et al. 2010). • American Association of State Highway and Transportation Officials (AASHTO) Roadway Lighting Design Guide, Seventh Edition (AASHTO 2018). • IES Policy on Roadway Lighting, RP-8-18 (IES 2018). • PennDOT Lighting Policy for Roundabouts (Rodegerdts and Myers 2020). • GDOT Evaluation of Current Practice for Illumination at Roundabouts (Rodgers et al. 2016). NCHRP Report 672, Roundabouts: An Informational Guide, Second Edition NCHRP Report 672 notes that roundabout lighting should account for the fact that a roundabout introduces geometry and channelization a driver may not expect. This may limit the effectiveness of headlights because of the curve radius of the approach as well as the circulatory and exit geometry that is not present in other intersection forms (e.g., two-way stop-controlled intersections). NCHRP Report 672 recommends lighting all roundabouts, and subsequent state guidance—such as those produced by Washington, Wisconsin, and Colorado—have adopted this recommendation into their standards (Rodegerdts et al. 2010).

83 American Association of State Highway and Transportation Officials (AASHTO) Roadway Lighting Design Guide, Seventh Edition The AASHTO Roadway Lighting Design Guide, Seventh Edition, provides a general overview of lighting systems from the perspective of state transportation departments and recommends minimum design parameters (AASHTO 2018). The document notes that the purpose of lighting at roundabouts can be to provide unfamiliar motorists with more navigational information than typical intersections. It also notes that geometric factors and landscaping in the central island and the need for quick decisions can warrant special attention compared to other intersection forms. Warrants for lighting include frequent fog, ice, snow, roadway geometry, ambient lighting, sight distance, signing, or other factors that a government agency finds sufficient. AASHTO recommends lighting a roundabout to a level 1.3-to-2 times the values used on the approach with the greatest light level and extending the lighting 400 ft from the roundabout along each connecting road (AASHTO 2018). Illuminating Engineering Society of North America (IES) Policy on Roadway Lighting, RP-8-18 The IES RP-8-18 notes that the following locations and user activities at a roundabout can benefit from illumination (IES 2018, sec. 12.4.3): • Uncertainty at the roundabout approach. • Pedestrian crosswalks. • Vehicle tracking around the circulatory roadway. • Drivers looking farther to the left than headlights can track. • Cyclists negotiating a roundabout. More generally, IES RP-8-18 presents three classifications of intersection lighting: • Full intersection lighting: used for intersections on one or more streets with continuous lighting. • Partial intersection lighting: used for areas within interchanges and for isolated intersections where no continuous lighting is provided on the intersecting streets. • Intersection delineation lighting: used to identify the location of an intersection. IES provides illuminance criteria based on roadway functional classification, pedestrian activity levels, and road surface classification for full and partial intersection lighting. IES also recommends transition lighting where continuous roadway lighting is not present for a length of at least 80 m (263 ft) from the roundabout on each approach. This language is unchanged from the Design Guide for Roundabout Lighting, DG-19-08 (IES 2008). There does not appear to be any substantiation in IES 2018 for why the illuminance values for isolated non-roundabout intersections were updated while those for isolated roundabouts remained the same. These recommendations may not account for the new partial lighting recommendations from IES, nor do they provide flexibility based on the lighting level of the roundabout or the context. Lighting guidance could be more flexible, and parallels can be drawn to transition lighting at tunnels, toll plazas, and rest areas. For tunnels, IES recommends that the approach and exit roadways should have a luminance level of no less than one-third of the tunnel interior level for one safe stopping sight distance (IES 2018, sec. 14.4.3). For exiting the toll collection area at toll plazas, IES recommends that a uniform reduction in the average illuminance level be maintained throughout the departure zone by reducing the average illuminance equally in steps no greater than three times the previous step until it matches that of the roadway (IES

84 2018, sec. 15.4). For rest areas, the access and egress roads are recommended to be lighted at a luminance of 0.6 cd/m2 (illuminance of 9 lux for R2/R3 pavement), with a higher luminance level for internal roads in rest areas. This information in IES RP-8-18 was used for PennDOT’s Lighting Practices, described below. PennDOT Lighting Practices PennDOT adopted a new lighting policy for roundabouts that adapts policies in NCHRP Report 672 and IES Policy on Roadway Lighting to provide increased flexibility in roundabout lighting (IES 2018; Rodegerdts and Myers 2020). PennDOT’s lighting policy adjusts the IES RP-8-18 recommendations by addressing gaps in the current guidance, rectifying inconsistencies, and increasing the ability for a designer to customize the lighting to different contexts and design components. The adopted policy adapts the IES method used for transition lighting at tunnels. The need for transition lighting is primarily dictated by the lighting level of the roundabout and the amount of time it takes for the human eye to adapt from a bright condition to a dark condition. If transition lighting is needed, the extent necessary is a function of the lighting level of the roundabout, the exit speed, and the speed limit downstream of the roundabout. The results of this analysis are summarized in Table 2. Key findings from the policy include: • The need for transition lighting is primarily dictated by the lighting level of the roundabout and the amount of time it takes for the human eye to adapt from a bright condition to a dark condition. o If transition lighting is needed, the extent of necessary transition is a function of the lighting level of the roundabout, the exit speed, and the speed limit downstream of the roundabout. • If the isolated intersection light levels in IES RP-8-18 are applied to roundabouts, no transition lighting is needed beyond the area closest to the roundabout. o This is because the lighting levels for isolated intersections are 9 lux (0.8 fc) or less; at these low values, IES suggests that no additional transition zones are needed. • If the Local/Local lighting levels are used for an isolated roundabout as recommended in IES RP- 8-18: o Roundabouts in low pedestrian activity areas (8 lux/0.7 fc) do not need transition lighting. o Roundabouts in medium or high pedestrian activity areas (14-18 lux/1.3-1.7 fc) need approximately 200-to-290 ft of transition lighting, with the distances varying depending on speeds. These are comparable to the fixed IES recommendation of 260 ft (80 m) but are sensitive to speed rather than being a fixed value. • Only roundabouts that are designed with the highest illuminance levels associated with Major/Major or Major/Collector intersections with medium-to-high pedestrian activity require the most extensive transition lighting, 340-to-540 ft. o This is comparable to the fixed AASHTO recommendation of 400 ft but is sensitive to speed rather than being a fixed value (AASHTO 2018). o This condition would be highly unusual for a truly isolated roundabout because the pedestrian activity and associated land uses would likely dictate continuous lighting along one or more of the intersecting roadways.

85 • Lower exit design speeds reduce the extent of transition lighting because drivers will start from a slower speed when accelerating away from the roundabout, adapting to dark conditions over a shorter distance. • Lower speed limits reduce the extent of transition lighting due to the assumed cap on speed once a driver has accelerated to the speed limit. • Zones are used to help identify lighting transitions at the roundabout as follows: o Zone 0—the roundabout, itself—includes the crosswalk area and is illuminated at the same level as the roundabout, itself. The extent of Zone 0 should be governed by the crosswalk position and by the need for vertical illuminance at the crosswalk in the direction of vehicular traffic. o Zone 0 will typically extend at least 20 ft beyond the farthest edge of the crosswalk. For crosswalks that are 10 ft wide and located 20 ft away from the circulatory roadway, this places the edge of Zone 0 at 50 ft from the edge of the roundabout. o For crosswalks located farther from the roundabout, Zone 0 should be extended accordingly. o If no crosswalks are present, a general assumption of 50 ft beyond the edge of the roundabout is appropriate. Table 2. Summary of Transition Lighting Policy Roundabout Illuminance Transition Lighting Needed beyond Zone 0? Transition Zone Length (ft) Zone 0 (100% of illuminance) Zone 1 (70%) Zone 2 (40%) Zone 3 (16%) Total >22 lux (>2.0 fc) Yes 50, or 20 beyond farthest edge of crosswalk 30-50 90-140 140-250 310-490 >13-22 lux (>1.2- 2.0 fc) Yes 50, or 20 beyond farthest edge of crosswalk 30-50 90-140 170-240 >9-13 lux (>0.8- 2.0 fc) Yes 50, or 20 beyond farthest edge of crosswalk 30-50 80-100 <=9 lux (<=0.8 fc) No 50, or 20 beyond farthest edge of crosswalk 50 Georgia Department of Transportation (GDOT) Evaluation of Current Practice for Illumination at Roundabouts In Evaluation of Current Practice for Illumination of Roundabouts, GDOT reviewed lighting practices across 44 countries, including 22 European countries, 12 Asian countries, 2 African countries, and 9 countries in the Americas outside the US. (Rodgers et al. 2016). The paper also built roundabout illumination models to compare annual operating costs corresponding to 15 selected countries’ policies. Most countries reviewed in the study (59%) do not require systematic illumination of roundabouts in rural areas, and few (16%) attempt to light all roundabouts. Additionally, the average minimum maintained

86 illuminance is higher in the US than in Europe. Common triggers for roundabout illumination included pedestrian volumes, presence of illumination in the immediate vicinity, presence of illumination on at least one approach street, availability of power, and location of the roundabout within one mile of a built- up area. The researchers examined safety data from Minnesota and concluded that partial illumination achieves significant benefits compared to leaving the roundabout unlit. They concluded with a “qualified yes” that it may be feasible to use a reduced illumination roundabout as a safety treatment for either uncontrolled or stop-controlled rural intersections (Rodgers et al. 2016). Internationally, the French lighting guide reports that two-thirds of all roundabouts in rural areas are not illuminated and that nighttime injury crashes are divided half-and-half among illuminated and unlit roundabouts. The guide also notes that almost all nighttime crashes involve the loss of control of single vehicles and result in property damage only; as a result, they are not as readily quantifiable (CERTU 1991). The researchers propose that if lower illuminance requirements were implemented, the increased implementation of roundabouts would have a net benefit to the safety of the highway system. Key Findings The key findings from the state of the practice review include the following: • Lighting makes the intersection visible from a distance and makes key conflict areas more visible. • Headlight effectiveness is reduced at roundabouts because of intersection geometry; a driver entering and circulating typically needs to look farther to the left than headlights can track, and lighting should be provided at roundabouts. • IES recommendations for roundabout lighting may not account for the new partial lighting recommendations from IES, nor do they provide flexibility based on the lighting level of the roundabout or the context. (IES 2018) • AASHTO Roadway Lighting Design Guide, Seventh Edition, and IES Policy on Roadway Lighting, RP- 8-18, identify transition lighting minimums that are not sensitive to factors such as exit speed and geometry. (AASHTO 2018; IES 2018) • Lighting guidance could be more flexible, and parallels can be drawn to transition lighting at tunnels, toll plazas, and rest areas. • PennDOT’s lighting policies provide flexible transition lighting guidance dictated by the lighting level of the roundabout and the amount of time it takes for the human eye to adapt from a bright condition to a dark condition (related to exit speed). (IES 2018; Rodegerdts and Myers 2020). • GDOT‘s Evaluation of Current Practice for Illumination at Roundabouts proposes that, if lower illuminance requirements were implemented, the increased implementation of roundabouts would have a net benefit to the safety of the highway system. (Rodgers et al. 2016).

87 4. MINI-ROUNDABOUT SYNTHESIS SUMMARY This synthesis summarizes mini-roundabout research findings. Mini-roundabouts require less right-of-way and are generally less expensive than single-lane or multilane roundabouts, potentially providing similar benefits at a lower cost. Much of the existing guidance states that mini-roundabouts are suitable treatments for locations with average annual daily traffic (AADT) less than 15,000 vehicles per day, roadway approach speeds less than 30-35 miles per hour (mph), and heavy vehicle volumes less than 3%. These criteria could potentially limit mini-roundabout implementation. In the last decade, mini-roundabouts have been installed in locations with higher volumes, higher speeds, and higher heavy vehicle presence. STATE OF THE PRACTICE REVIEW The state of the practice review summarizes the findings and policies from the following documents: • NCHRP Report 672, Roundabouts: An Informational Guide, Second Edition (Rodegerdts et al. 2010) • The FHWA Mini-Roundabouts Technical Summary (FHWA 2010) • The unpublished 2016 FHWA Mini-Roundabouts: Before and After Successful Case Studies Report (FHWA 2016) • Oregon DOT Mini-Roundabout Guidance (Kittelson et al. 2019) NCHRP Report 672, Roundabouts: An Informational Guide, Second Edition NCHRP Report 672 provides geometric, operational, safety, and related information about roundabouts, including mini-roundabouts (Rodegerdts et al. 2010). Mini-roundabouts are recommended primarily for locations where: • There are perpendicular approaches to the roundabout. • All approaching roadways have an 85th percentile speed of less than 30 mph. • Retrofit applications are necessary. According to NCHRP Report 672, certain applications not well-suited for mini-roundabouts include (Rodegerdts et al. 2010): • Locations where high U-turn traffic is expected. • Locations with high volumes of heavy vehicles. • Locations with heavily skewed approaches. Similar to other types of roundabouts, mini-roundabout planning and design should consider pedestrians, bicyclists, trucks, transit, and emergency responders in planning-level screening. A mini-roundabout can generally serve up to a 15,000 daily entering volume (e.g., 5,000 AADT for two approaches and 10,000 AADT for the other two). The capacity threshold can be estimated at 1,000 vehicles per hour for any approach leg’s conflicting entering and circulating volumes (e.g., 400 vehicles entering an approach with 600 vehicles circulating in front of that entry) or possibly up to 1,300 vehicles per hour given ideal conditions. Factors that impact capacity include the percentage of left turns, heavy vehicle presence, pedestrian presence, and the balance of approaching traffic.

88 FHWA Mini-Roundabouts Technical Summary The FHWA Mini-Roundabouts Technical Summary provides an overview of the key considerations needed for the planning, analysis, and design of mini-roundabouts (FHWA 2010). Although mini-roundabouts have unique characteristics, the planning, analysis, and design require the same “principles-based approach” as all roundabouts. According to the technical summary, mini-roundabouts are particularly well suited for the following site characteristics: • Space-constrained locations with approach speeds of 30 mph or less. • Residential environments (low-speed, low-noise intersection). • Intersections with high delay (particularly stop-controlled intersections that do not meet signal warrants). Mini-roundabouts are not well-suited for the following site characteristics: • Locations where roadway speeds exceed 30 to 35 mph. • Intersections with more than four legs. o There may be sufficient spacing between legs to employ two closely-spaced mini- roundabouts. • Locations where heavy vehicles need to make U-turns. When the FHWA summary was published, mini-roundabouts were emerging in states like Maryland and Michigan. The information presented in the FHWA document relies primarily on guidance and experience in countries where mini-roundabouts are common (including the United Kingdom and France) and incorporates guidance from the United States where appropriate. The summary discusses the many benefits of mini-roundabouts, including compact size, operational efficiency, traffic safety, traffic calming, access management, aesthetics, and environmental benefits. (FHWA 2010) The FHWA summary considers the following design accommodations for different mini-roundabout users: • As there is sometimes insufficient space for a pedestrian refuge, pedestrians will need to cross mini-roundabouts in one stage. According to the summary, the pedestrian crossing should be located 20-to-25 ft upstream of the entrance line. • Bicyclists are expected to comfortably use the same lane as motor vehicles to navigate the mini- roundabout. If a bike lane is present leading up to the roundabout, it should end 100 ft upstream of the entrance line. • Emergency vehicles are expected to traverse the central island and splitter islands. • Transit should be accommodated in the circulatory roadway without using the center island. The FHWA technical summary also provides design guidance for mini-roundabouts (FHWA 2010). • The inscribed circle diameter should not exceed 90 ft; anything above this diameter is sufficient space for a single-lane roundabout with physical channelization to control vehicle speeds. • The “the center island should be domed using 5to 6 percent cross slope, with a maximum height of 5 inches.” • Three types of splitter islands can be used depending on the site conditions: raised (non- traversable), mountable (traversable), or flush (painted). • Pavement markings are like those for other roundabouts, but “additional pavement markings can be used to improve the visibility of key features.”

89 • Mini-roundabouts require the same lighting principles as traditional intersections. The FHWA technical summary also provides a brief insight into the following design details and applications: • Right-turn bypass lanes • Access management • At-grade rail crossing evacuation routes • Bus stops The FHWA technical summary provides site-related factors that “may significantly influence the design” and states that many of the factors are valid for all intersection types. The technical summary also states these conditions do not necessarily “preclude the installation of a mini-roundabout” but, rather, that “additional analysis, design work, and coordination with affected parties may be needed to resolve conflicts and help with the decision-making process.” (FHWA 2010) FHWA Mini-Roundabouts: Before and After Successful Case Studies Unpublished Report FHWA created a draft report that guides design, operations, and safety elements for mini-roundabouts (FHWA 2016). It includes a case study of 15 sites in a variety of contexts to determine suitable environments. The report recommends the following design elements for mini-roundabouts: • The central island should be fully mountable and 12-to-25 ft in diameter. • The circulating lane should be 14-to-16 ft wide. • Splitter islands should be more than 4 ft wide and 45 ft long. • ADA pedestrian crossings should be 10 ft wide and 20 ft upstream from inscribed circle. • Entry lanes should be single-lane entry and departure and should be 10-to-11 ft wide. • The entrance angle requires adding deflection to control approach speed. The report provides a total hourly volume (entering on all approaches) of 1,600 vehicles per hour. This can be used as an initial high-level screening threshold, with a second level of planning-level capacity analysis considering each entry’s entering and circulating volumes. (FHWA 2016) The report considers the following site elements as supportive of a mini-roundabout: • Annual average daily entering traffic less than or equal to 15,000. • Posted speed limit less than or equal to 35 mph. • Truck volume less than or equal to 3%. o Assumes heavy vehicles will traverse the raised elements of the mini-roundabout. • Comparable major/minor traffic volumes. Based on the case studies presented in the draft report, the following environments were documented as most suitable for mini-roundabouts (FHWA 2016): • “Sites in urban and suburban environments. Also, successfully applicable to rural sites with heavy traffic volumes and low or moderate speed limits.

90 • Sites with two-way or all-way STOP controlled with single[-]lane approaches; mini-roundabouts show excellent ability to unclog bottlenecks at AWSC intersections, and to provide safer gaps to minor road traffic at TWSC intersections. • Sites with any budget limits; mini-roundabout installation can vary from tens of thousands of dollars to as high as hundreds of thousands of dollars. Sites with ample budget availability can add aesthetic features that help preserving neighborhood and property values. • Sites with low approach speed limits; mini-roundabouts show ability to reduce speeding and stop sign running. For high[-]speed sites, although it showed major operational improvements, some safety concerns still exist. • Sites with medium and heavy volumes; mini-roundabouts show substantial capacity improvements, queue reductions, and delay and travel time reductions. • Sites with light volumes did not show much improvements. • Sites with high non-motorized interactions; mini-roundabouts show improved accessibility for pedestrians and bicycles and attracts more school age children to walk to school. • Sites with limited available footprint and any right-of-way constraints; mini-roundabouts eliminate the need for utility relocations and/or land acquisitions.” (FHWA 2016) The report defined thresholds for what should be considered “high non-motorized interactions.” These thresholds are: • Light volume: less than 5,000 AADT. • Medium volume: between 5,000 and 10,000 AADT. • Heavy volume: greater than 10,000 AADT. The report does not state whether any of the locations exceeded an AADT of 15,000. (FHWA 2016) Oregon Department of Transportation (ODOT) Mini-Roundabout Guidance This guidance was developed to evaluate the feasibility of installing a mini-roundabout at an existing stop- controlled intersection in Sisters, Oregon (Kittelson et al. 2019). The purpose of the evaluation was to identify which features of a mini-roundabout affect operational performance and to identify typical analysis protocols for mini-roundabouts that can be applied to other ODOT intersections. The capacity of a mini-roundabout is not well established in the United States; however, NCHRP Report 672 states that mini-roundabouts can serve AADT up to 15,000 and peak hour conflicting volumes of up to 1,300 (Rodegerdts et al. 2010). Kittelson calibrated a microsimulation analysis using a VISSIM model for approach speed, traffic volume, and congestion for the existing stop-controlled intersection but did not include calibration to an existing roundabout. The study evaluated the potential operational and safety benefits of installing a mini- roundabout at intersections that currently exhibit congestion. This study was based on a VISSIM model not calibrated by real-world data. Further empirical research is needed to determine the capacity of mini-roundabouts.

91 Key Findings The key findings and feasibility factors from the state of the practice review are as follows: • Mini-roundabouts are recommended primarily for locations where: o There are perpendicular approaches to the roundabout. o All approaching roadways have an 85th percentile speed of less than 30 mph. o There is up to 15,000 daily entering volume o Retrofit applications are necessary. o Intersections have high delay (particularly stop-controlled intersections that do not meet signal warrants) • According to the guide, certain applications not well-suited for mini-roundabouts include: o Locations where high U-turn traffic is expected. o Locations with high volumes of heavy vehicles. o Locations with heavily skewed approaches. o Locations with more than four legs. TRANSPORTATION AGENCY OUTREACH The transportation agency outreach section summarizes mini-roundabout guidance documents representing the following agencies: • Washtenaw County, MI • King County, WA • Harford County, MD • Scott County, MN The guidance from each contact is described in the following sections. Washtenaw County, MI Communication with Washtenaw County, Michigan, revealed anecdotal guidance for mini-roundabouts in Washtenaw County related to approach speed, safety, sight distance, and operations during winter weather conditions. Although mini-roundabouts are typically designed for roads with speeds of 35 mph or less, they can be used on higher speed roads with proper speed reduction designs and treatments. Washtenaw County has mini-roundabouts with approach speeds as high as 55 mph that continue to have good speed compliance. Drivers traveling straight generally travel 25 mph through the mini-roundabout, and drivers turning travel at slower speeds. The county received some complaints about drivers traveling approximately 45 mph approaching the roundabout and only slowing within approximately 300 ft of the intersection, which often occurs with stop-controlled or signalized intersections on higher-speed roadways. The county also provided anecdotal safety information for two mini-roundabouts. There were three significant injury crashes total over the past three years at the two mini-roundabouts. Two of those crashes were alcohol-related, and the final was a sideswipe crash involving a motorcyclist. They have no other reported injury crashes at mini-roundabouts in recent years. There has been approximately one property-damage only crash per month at each mini-roundabout, which is greater than what typically occurs at a roundabout. This may be because there is a shorter travel distance between legs on the roundabout, so drivers have less reaction time to determine if there is a sufficient gap for them to enter

92 the roundabout. Communication with the County revealed that sight distance requirements should be studied further as they relate to mini-roundabouts. In Washtenaw County, they design the roundabouts to provide 50 ft of sight distance from the yield line on each leg, but further research is needed to confirm this approach. Washtenaw county has not had reported complaints or safety concerns related to roundabout operations during winter conditions. Drivers continue to navigate the roundabout appropriately when there is snow on the road, and they typically drive slower when it is snowing to provide additional time for stopping, reacting, and decision making. King County, WA Communication with King County, Washington, revealed anecdotal guidance for mini-roundabouts related to traffic operations, safety, and design flexibility. Communication with the County revealed that the Redmond Town Center mini-roundabout, which includes an oval design to accommodate a skewed approach, manages over 15,000 AADT and serves heavy pedestrian volumes, serves high peak hour volumes, and has on-street parking on most approaches. Despite this, it had not had a reported crash between its installation. Within King County, mini-roundabouts typically serve lower AADT, though they have several in the 10,000- 11,000 AADT range. A recent mini-roundabout installation in Fairwood that serves higher AADT volumes has not reported any crashes in the eight months of its operation (November 2019). The County noted that traffic volumes have been lower due to the impacts of COVID-19 and that the County plans to continue monitoring activity and safety as traffic volumes return. King County installed a mini-roundabout at the intersection of an arterial and local road where people were previously observed speeding at close to 70-80 mph and several severe crashes had been recorded. Within the first few months of its installation, the intersection had four single-vehicle run-off-the-road crashes with minor injuries from speeders. Additionally, speeding incidences have now decreased to zero crashes at the roundabout since installation. King County coordinates with its transit agencies to help drivers understand how to navigate through mini- roundabouts. The County also uses several sets of raised pavement markers on the edge of splitter islands to show drivers where to begin their turn and adjust as they circulate. Drivers who used to get “pinched in” mini-roundabouts now report feeling comfortable driving through the intersection. Harford County, MD Harford County, Maryland, noted that they did not have information to provide on mini-roundabouts. Scott County, MN Communication with Scott County, Minnesota, revealed anecdotal guidance for mini-roundabouts related to safety performance. The County provided annual crash data for the County Highway 79/Vierling Drive intersection before and after constructing the first mini-roundabout in Minnesota (constructed in 2014). The intersection met the following FHWA criteria: • The intersection was exhibiting capacity and/or safety issues. • The total entering volume was less than 1,400 vehicles per hour.

93 • There were low truck volumes. • There were no nearby commercial driveways. The intersection did not meet the following criteria: • Low heavy vehicle volumes: School buses travel in the roundabout during off-peak hours. • Low-speed roadway: The roadway was “not quite” a low-speed roadway, with posted speed limits up to 45 mph on some approaches. The intersection has exhibited higher crash rates after conversion to a mini-roundabout, but there have been no noticeable trends documented in the crashes. The most significant difference the County noticed when comparing the safety benefits of the typical single-lane roundabout to a mini-roundabout is the required visual inventory for a driver entering the intersection. Due to the closeness of all movements in a mini-roundabout, the driver must consider the vehicles at all legs of the intersection, rather than focusing on the leg to their left. Communication with the County noted that while there are benefits to mini-roundabouts, it is important to fully assess the situation and what the safety and mobility goals are for the intersection. Key Findings The key findings from the state of the practice review include the following: • Mini-roundabouts have several advantages over typical single-lane roundabouts, such as: o Requiring less right-of-way. o Reducing installation cost. • A mini-roundabout may be able to be designed to accommodate over 15,000 AADT. • Although mini-roundabouts are typically designed for roads with speeds of 35 mph or less, they can be used on higher-speed roads with proper speed reduction designs and treatments. • Transit driver—and potentially truck drivers—comfort and ability to operate a bus through a mini- roundabout can be improved by constructing raised pavement markers on the edge of splitter islands to show drivers where to begin their turn and where to adjust. • Jurisdictions observed mixed safety performance at intersections converted to a mini- roundabout. o Mini-roundabouts require drivers to take a wider visual inventory of the whole intersection compared to a traditional roundabout, where drivers may focus on tasks at the entry.

94 5. IN-SERVICE ASSESSMENT AND RETROFIT SYNTHESIS SUMMARY The roundabout practice has evolved to the extent of now having existing roundabouts to assess. This synthesis establishes a framework for assessing existing roundabouts and identifying methods to consider potential remediation approaches based on in-service performance. This synthesis also provides information about how roundabout design principles can apply to rotaries and other circular intersections for possible retrofit strategies. ASSEMBLED EXAMPLES OF RETROFITS The research team assembled a list of retrofitted roundabout examples by filtering through the Kittelson Roundabout Database (Kittelson 2022) and collecting known examples from the Literature Assembly. The list resulted in 54 retrofitted roundabouts. Kittelson screened the locations to identify 22 retrofitted roundabouts, removing locations with planned changes (e.g., additional lanes or legs that were originally considered in design or conversion from temporary to permanent configurations). Additional screening was conducted to remove locations where no or poor quality before-and-after imagery was available. The final screening step resulted in 15 retrofitted roundabouts. Common modifications to these roundabouts included lane reductions, horizontal and vertical geometric changes, and signing and striping changes. Other modifications included converting existing circular intersections and rotaries to roundabouts. APPLYING PERFORMANCE CHECKS TO IN-SERVICE ASSESSMENTS NCHRP Report 672, Roundabouts: An Informational Guide, Chapter 6 (Exhibits 6-1) presents an iterative design process to size and configure roundabouts of various types (Rodegerdts et al. 2010). A key element of the iterative process is conducting performance checks to assess if a given configuration meets intended performance metrics. These metrics include speed, design users, and specific operational elements associated with multilane configuration (natural path). Chapter 6 describes how size, position, and approach alignment can influence predicted performance and how to assess that performance. Ideally, geometric designs should be modified and refined until an optimal performance for a given location is attained. Early in the roundabout planning and design practice, the nuances of geometric design and the resulting operational effects of that geometry was sometimes not considered or fully understood. There also may have been various constraints (e.g., environmental, economic, political). Rotaries were developed before modern roundabouts and often did not include features or qualities that result in desired roundabout performance. In other cases, roundabouts have been constructed with features or qualities that result in undesired operations or safety performance. While it is ideal to address these elements during design, the information in Chapter 6 can be applied to in-service assessments by diagnosing possible factors contributing to undesirable safety performance, operational performance, or both along with applying performance check principles to help with possible mitigations. Considering the Chapter 6 design elements associated with attaining target performance, Kittelson assessed the before condition of the filtered sites and identified common geometric configurations that could have contributed to the changes at each site. If the roundabouts had been evaluated using these performance checks during the design stage, the intersection configuration could have provided clues to

95 possible adverse performance. This is a theoretical exercise, as actual design decision-making considerations cannot be known. However, the actual background can be effectively ignored, as the review exercise is based on lessons learned when assessing intersection geometrics and understanding how to consider possible mitigations. PERFORMANCE CHECKS This section categorizes the assembled list of retrofits by the performance check(s) that identify issues, such as fastest path, path alignment, sight distance, and angles of visibility. Route 188/Route 334 (Great Hill Road)/Holbrook Road – New Haven County, CT This roundabout (Figure 1) included skewed approach cross streets and entry approach configurations that promote high speeds. Entry and circulatory lane widths also supported higher speeds, and the roundabout did not include pedestrian crossing elements. This retrofit modified approach geometry to reduce entering, circulatory, and exit speeds. This includes additional curvature on all approaches to create deflection, reducing the circulatory roadway width to better confine vehicles navigating the circulatory roadway, and outer curb additions to confine travel paths and support alignment. Before After Source: Google Earth Figure 1. Route 188/Route 334 (Great Hill Road)/Holbrook Road – New Haven County, CT

96 Route 80/Route 81 – Killingworth, CT This roundabout (Figure 2) had features similar to Route 188/Route 334 in New Haven County, Connecticut, including skewed approach cross streets and entry approach configurations that promote high speeds. The splitter islands were painted, and the entry and circulatory roadway widths supported higher speeds and did not provide positive channelization with raised splitter islands and a truck apron. This retrofit modified the approach geometry to reduce entering, circulatory, and exit speeds, which includes adding a mountable truck apron and outer curbs to reduce speeds while accommodating larger vehicles. The retrofit also includes adjusting and introducing raised features at the splitter islands. Before After Source: Google Earth Figure 2. Route 80/Route 81 – Killingworth, CT

97 Walnut Lane/Park Line Drive – Philadelphia, PA Similar to the Route 188/Route 334 and Route 80/Route 81 locations, this roundabout (Figure 3) included skewed approach cross streets and entry approach configurations that promote high speeds. This retrofit converted a circular intersection with a stop-controlled approach and two stop-controlled sections of circulatory roadway to a roundabout. The modification included raised features and approach geometry modifications to reduce overall speeds and reduce speed differentials. The modification also improved view angles where previous angles exceeded the recommended 75 degrees. Before After Source: Google Earth Figure 3. Walnut Lane/Park Line Drive – Philadelphia, PA

98 Cemetery Road/Main Street – Hilliard, OH This multilane roundabout (Figure 4) was built in a constrained footprint, limiting the ability to adjust size, location, and approach geometry. With little deflection, the roundabout in the before condition exhibited entry and exit speeds of 20-to-28 miles per hour (mph). The retrofit added raised pedestrian crosswalks to improve pedestrian comfort and decrease speeds; modified striping to improve entry, circulatory, and exit positioning; and narrowed entry lane widths. The resulting speeds after improvements were 14-to- 19 mph on entry and 19-to-24 mph on exit. Before After Source: Google Earth, Kittelson & Associates, Inc. Figure 4. Cemetery Road/Main Street – Hilliard, OH

99 US 50/US 15 – Gilberts Corner, VA This multilane roundabout (Figure 5) had features similar to the skewed approach and entry configurations that promoted high speeds at Route 188/Route 334 and Route 80/Route 81. However, it also had two-lane entries on the north and south legs. The two entry lanes provided more capacity than necessary, leading to more conflict points. This roundabout exhibited 67 reported crashes in a two-year period, with identified potential issues being high entry speeds, volume patterns, excessive sight distance, and signing/pavement markings. The revised single-lane roundabout removed lanes and excessive pavement to reduce conflict points and speeds. Before After Source: Google Earth Figure 5. US 50/US 15 – Gilberts Corner, VA

100 MD 175/MD 677/Higgins Drive – Odenton, MD This roundabout (Figure 6) had five approach legs, including three with two lanes each, and an inscribed diameter that led to limited deflection on the southbound entry. This could result in issues with an undesirable entry speed and relatively high-speed differentials for circulating vehicles. The retrofit resulted in a single-lane roundabout with fewer entry, circulating, and exit lanes to provide increased deflection on entries and exits, a narrower circulating width, and fewer conflict points. Before After Source: Google Earth Figure 6. MD 175/MD 677/Higgins Drive – Odenton, MD

101 MD 198 (Laurel Fort Meade Rd.)/MD 32 EB Ramps – Jessup, MD Similar to Gilberts Corner, the skew condition of this roundabout (Figure 7) limited deflection on some approaches, which promotes high speeds. The presence of multilane entries on two legs amplifies the negative speed effects of the skew. The circulatory roadway was unstriped and had no truck apron or buffer to the non-traversable central island. The retrofit reduced the number of entry lanes on the eastbound approach, reduced the circulatory lane width and number of lanes on several sides, increased deflection on two entries to reduce speed, and delineated the circulatory roadway to a single lane in portions where two lanes were not necessary. Before After Source: Google Earth Figure 7. MD 198 (Laurel Fort Meade Rd.)/MD 32 EB Ramps – Jessup, MD

102 MD 198 (Laurel Fort Meade Rd.)/MD 32 WB Ramps – Jessup, MD The issues associated with this roundabout (Figure 8) were similar to the eastbound ramps at this interchange, though this intersection did not have the same pronounced skew. The retrofit reduced the number of exit lanes on the north leg, reduced the number of circulatory roadway lanes on portions of the roundabout, reduced the north leg exit to a single lane, and delineated the remaining multilane circulatory section. Located outside the view of the after picture are left-turn-only and left-through-right lane use arrow pavement markings on the east leg (the MD 32 westbound offramp). Before After Source: Google Earth Figure 8. MD 198 (Laurel Fort Meade Rd.)/MD 32 WB Ramps – Jessup, MD

103 SW 29th Street/Urish Road – Topeka, KS The original multilane entry to this roundabout (Figure 9) had inadequate deflection, resulting in undesirable entry speeds. The multilane exits had relatively small exit radii that created path overlap. The retrofit removed a circulatory lane on the north side to achieve a larger exit radius and reduce conflict points at the intersection. The westbound entry lanes changed from a left-turn lane and a shared through/right-turn lane to a shared left/through lane and a right-turn lane, balancing lane use on this approach. Before After Source: Google Earth Figure 9. SW 29th Street/Urish Road – Topeka, KS

104 Steptoe Dr./SR 240 EB Ramps/Columbia Park Trail – Richland, WA The multilane entries to this roundabout (Figure 10) had path overlap and limited deflection to support speed reduction on entry. The two-lane exits had path overlap associated with the relatively small radii on departure. The retrofit reduced the number of eastbound and westbound entry lanes and reduced the circulatory lanes on the north and south sides, resulting in lower speeds and fewer conflict points. Additionally, reconfiguring to a single exit lane on the west leg eliminated the exit path overlap. Before After Source: Google Earth Figure 10. Steptoe Dr./SR 240 EB Ramps/Columbia Park Trail – Richland, WA

105 Jacaranda Boulevard/Venice Avenue – Sarasota, FL This roundabout (Figure 11) had a relatively large diameter and was constructed with multilane entries that resulted in expansive pavement area. The distance between multilane entries and exits created a merge/diverge condition in parts of the circulatory roadway. Some entries had minor path overlap, while relatively small exit radii created path overlap. The retrofit reduced the number of some entry and exit lanes while also reducing the number of circulating lanes on the north side to adjust entry and exit alignment. The retrofit condition includes striped gore areas on approaches that narrow lane width and align vehicles on entry. Before After Source: Google Earth Figure 11. Jacaranda Boulevard/Venice Avenue – Sarasota, FL

106 SR 161/Riverside Drive – Dublin, OH This roundabout (Figure 12) had skew on the north and south approach roadways that created a relatively long distance between the westbound entry and northbound exit. The northbound entry had path overlap, uneven lane use, and high entry speeds. The retrofit changed the entry lane assignments, converting from a dedicated left-turn, through, and shared through-right to a shared left-through, through, and dedicated right-turn lane. The change balanced volumes, allowed for the removal of a circulatory lane, and corrected path alignment. The retrofit also introduced striped gore areas on approaches to narrow lane width and align vehicles on entry. Before After Source: Google Earth Figure 12. SR 161/Riverside Drive – Dublin, OH

107 ROTARIES Rotaries include several geometric features identified in the previous examples that can promote high speeds and create merge/diverge areas in the circulatory roadway. High-speed maneuvers degrade safety performance and can result in increased congestion due to longer decision times required at faster speeds. Table 3 shows what rotary design elements allow or exacerbate undesired driving behaviors. Table 3. Rotary Design Elements and Associated Driving Behaviors Rotary Design Element Driving Behavior Large ICD Promotes increased circulating speeds and creates sections of circulatory roadway that induce merging, diverging, and weaving behavior. Wide, undefined circulatory roadway Induces weaving maneuvers that, when combined with large ICD, are more challenging when combined with higher speeds. Lack of splitter islands Provide insufficient channelization to restrict wrong-way maneuvers while promoting increased entry speeds. Higher entry speeds can promote reverse priority where circulating drivers yield to entering vehicles. Acute angle entry geometry Poor viewing angle of circulating traffic may lead to abrupt braking at the yield line or disregard of the yield sign. Mixed entry controls Stop signs on entry or stop or yield signs within the circulatory roadway can violate a driver’s expectation of yielding on entry at a rotary. The following sections show several rotary retrofits that reduced or eliminated the design elements noted above, promoting slower speeds and shorter decision times.

108 Route 12/Main/Reaville – Flemington, NJ Before After Source: Google Earth Figure 13. Route 12/Main/Reaville – Flemington, NJ Copeland Circle – US 1 Ramps/Route 60 (Squire Rd.) – Revere, MA Before After Source: Google Earth Figure 14. Copeland Circle – US 1 Ramps/Route 60 (Squire Rd.) – Revere, MA

109 MacArthur Boulevard (Route 28)/Connery Avenue/Sandwich Road (Route 28A) – Bourne, MA Before After Source: Google Earth Figure 15. MacArthur Boulevard (Route 28)/Connery Avenue/Sandwich Road (Route 28A) – Bourne, MA KEY FINDINGS Table 4 shows the performance checks, the contributing factors to undesirable performance, and the typical retrofit modifications that may help to meet performance checks. Additionally, this table highlights the sites discussed above that exhibited these factors and modifications. As shown, some factors that lead to adverse performance can be assessed using several performance checks. Ideally, these issues can be mitigated early in the design process by identifying design features that contribute to fastest path and view angle challenges, such as intersection skew. When conducting in-service roundabout reviews, understanding factors that could contribute to undesirable performance and completing performance checks is the first step toward understanding potential mitigations. Potential modifications can be considered and evaluated within site-specific constraints. Roundabout design is often a matter of optimizing the configuration to attain adequate performance. Even if desired performance cannot be fully attained, a roundabout retrofit is often appropriate because of its beneficial safety and operational performance.

110 Table 4. Performance Checks, Contributing Factors, and Typical Retrofit Modifications Performance Check Contributing Factors to undesirable Performance Typical Modifications to Address Issue Example Sites Fastest Path • Skew • Suboptimal deflection • Wide lanes • Modifying the entry horizontal geometry to increase deflection • Reducing lane numbers • Narrowing lane widths • Including or increasing raised features (e.g., splitter islands and truck aprons) • Route 188/Route 334 • Route 80/Route 81 • Walnut Lane/Park Line Drive • Cemetery Road/Main Street • US 50/US 15 • MD 175/MD 677/Higgins Drive • MD 198 Ramps Path Alignment • Limited tangent on entry • Small radii on exit • Modifying the horizontal geometry to better align entering vehicles to their intended circulatory lanes • Modifying lane assignments • Modifying or adding striping • Lane reductions on exit • Cemetery Road/Main Street • SW 29th Street/Urish Road • Steptoe Drive/SR 240 EB Ramps/Columbia Park Trail • Jacaranda Boulevard/ Venice Avenue • SR 161/Riverside Drive Sight Distance • Skew • Excessive raised features (limits stopping sight distance) • Limited raised features (excessive sight distance promotes higher speed) • Modifying the entry horizontal geometry • Adding or removing raised features • US 50/US 15 Angles of Visibility • Skew • Modifying the entry horizontal geometry • Walnut Lane/Park Line Drive

111 6. PEDESTRIAN CROSSINGS SYNTHESIS SUMMARY NCHRP Report 834, Crossing Solutions at Roundabouts and Channelized Turn Lanes for Pedestrians with Vision Disabilities presents guidance on applying crossing solutions at roundabouts and channelized turn lanes at signalized intersections for pedestrians with vision disabilities (Schroeder et al. 2016a). NCHRP Report 834 is supplemented by NCHRP Web-Only Document 222 and FHWA TOPR 34: Accelerating Roundabout Implementation in the United States, which include additional documentation and background information on project research (Schroeder et al. 2016b; Rodegerdts et al. 2015). In addition, two chapters of NCHRP Report 834 were revised under NCHRP Project 03-78c (in publication as of this writing). STATE OF THE PRACTICE REVIEW The following sections provide the detailed results of the state of the practice review. NCHRP REPORT 834, CROSSING SOLUTIONS AT ROUNDABOUTS AND CHANNELIZED TURN LANES FOR PEDESTRIANS WITH VISION DISABILITIES NCHRP Report 834 provides an entire chapter on wayfinding principles (Chapter 3), with insights into the pedestrian’s decision-making process described by both previous research and observations from Certified Orientation and Mobility Specialists (COMS) (Schroeder et al. 2016a). Wayfinding has particularly applicable principles for both approaching the crosswalk and navigating through the crosswalk that have direct applications in roundabout design. These are the relevant sections include: • Section 3.1.1, Issues and Principles of Wayfinding at Intersections. • Section 3.1.2.1, Determining the Appropriate Crossing Location. • Section 3.1.2.2, Aligning to Cross and Establishing the Correct Heading. • Section 3.2.1, Issues and Principles for Determining When to Cross. • Section 4.1.1, Crosswalk Location and Angle Options. • Section 4.1.3, Buffering. • Section 4.2.1, Type of Traffic Control Device. • Sections 4.2.2, Location of Vehicle Signal/Beacon Faces. • Section 4.2.3, Location of Pedestrian Signal Faces and Accessible Pedestrian Signals. • Chapter 6, Wayfinding Assessment. • Chapter 7, Crossing Assessment.

112 NCHRP WEB-ONLY DOCUMENT 222, GUIDELINES FOR THE APPLICATION OF CROSSING SOLUTIONS AT ROUNDABOUTS AND CHANNELIZED TURN LANES FOR PEDESTRIANS WITH VISION DISABILITIES NCHRP Web-Only Document 222 is the draft final report of NCHRP Project 03-78B as well as a companion document to NCHRP Report 834 (Schroeder et al. 2016b). Much of the material in NCHRP Web-Only Document 222 that would be considered for inclusion in the revision to NCHRP Report 672 is also found in NCHRP Report 834 and has been discussed above. Besides the material that is duplicative of the content from NCHRP Report 834 mentioned above, the discussion of exit radii in the conclusions and findings in NCHRP Web-Only Document 222, Chapter 6, Conclusions, is useful for describing real-world applications of design decisions. “NCHRP Web-Only Document 222 presents the following findings related to exit radii and curvature: • “An increase in the degree of curvature (smaller radii and shorter curves) correlates with a decrease in frequency of interventions for visually impaired pedestrians. Roundabout exit legs, on average, tend to have smaller degrees of curvature (larger radii) than entry legs, and are on average associated with greater frequency of interventions. • An increase in the degree of curvature at the exit can be associated with improved visibility, which can facilitate the placement and visibility requirements for traffic signals, if those are part of the treatment solution for the roundabout. Providing clear line of sight between the pedestrian waiting area and approaching vehicles has further proven to be a very critical criterion for making a site accessible, which can for example be achieved by moving the exit portion of the crosswalk further away from the circulating lane. • An increase in the degree of curvature (smaller radii and shorter curves) correlates with a decrease in the free-flow speed at the crosswalk. Free-flow speeds were generally higher at roundabout exit than at entry, which often correlates with general design and radius between the two. As curvature at entries and exits increase, free-flow speeds are expected to decrease. • A decrease in free-flow speed correlates with an increase in the probability that drivers yield to pedestrians. With generally higher free-flow speeds at roundabout exits than entries, the associated yield probabilities are also lower at exits than entries.” (Schroeder et al. 2016b) “The study by Schroeder, et al described in the FHWA TOPR 34 report suggests that a threshold for interventions may exist at a roundabout entry and exit radius of around 91.4 m (300 ft). Note that this radius is not the same as the central island radius/diameter, but rather the radius that controls the speed at the crosswalk. For roundabout entries, the R1 radius most closely describes this parameter, and at roundabout exits, the R3 term is a reasonable approximation (although speeds for vehicles may be limited by the speed in the roundabout and an acceleration constraint). At entry crosswalks at two-lane roundabouts in the FHWA study, where all approaches had a radius of less than 91.4 m (300 ft), all percent interventions were less than 10 percent, and 9 out of 11 approaches had less than 5 percent intervention. This finding does not imply that all crosswalks with a controlling vehicle path radius of greater than 91.4 m (300 ft) are assured to be less accessible, nor that all crosswalks with a controlling vehicle path radius of less than 91.4 m (300 ft) are assured to be more accessible. But the findings may suggest that 300 ft is a potential classifying threshold for distinguishing “small” and “large” radii. A 300-ft radius should generally be sufficient to accommodate most design vehicles, and it is much larger than turns at traditional signalized intersections.” (Schroeder et al. 2016b)

113 “From the same FHWA research, a threshold is also evident in the relationship between vehicular free-flow speed at the crosswalk and percent intervention. The observed percent interventions changed noticeably at a vehicular free-flow speed around 35 km/h (22 mph); sites with higher speeds tended to have more than 10 percent intervention, while sites with lower speed tended to have less than 10 percent intervention (most sites less than 5 percent intervention). This finding does not imply that all crosswalks with free-flow vehicular speeds greater than 35 km/h (22 mph) are inaccessible, nor that all crosswalks with free-flow speeds less than this value are accessible. But the findings may suggest that 22 mph is a potential classifying threshold for distinguishing “low” and “high” speeds” (Schroeder et al. 2016).” FHWA REPORT FHWA-SA-15-069, ACCELERATING ROUNDABOUT IMPLEMENTATION IN THE UNITED STATES – VOLUME I OF VII: EVALUATION OF RECTANGULAR RAPID-FLASHING BEACONS (RRFB) AT MULTILANE ROUNDABOUTS This document is the report from Task Order Proposal Request (TOPR) 34 that most directly applies to the topics addressed in this synthesis (Rodegerdts et al. 2015). The report presents results from a pedestrian accessibility study evaluating the effectiveness of RRFBs at multilane roundabouts in the United States and describes the research team’s activities to conduct the study and produce the results. The findings from this study form the basis for some of the guidelines and recommendations found in NCHRP Report 834 and NCHRP Web-Only Document 222, and are generally incorporated into the findings, suggestions, and recommendations described above.

114 7. Traffic Control Devices – Metering Synthesis Summary One of the advantages roundabouts is the ability to manage traffic flow and conflicts at an intersection for a wide range of volumes without relying on a traffic control signal. Although counterintuitive, there may be circumstances where signalizing one or more approaches of a roundabout can improve the operations of the roundabout. Providing signal control at one or more approaches of a roundabout is referred to as roundabout metering. Roundabout metering may be appropriate when the circulating volumes are so high that there are not adequate gaps within the circulating traffic for vehicles from an approach to enter. Metering a roundabout may provide one or more of the following benefits: • Stopping traffic on one approach creates gaps in the circulating traffic that allows traffic from another approach to enter the roundabout. • Creating gaps in the circulating traffic reduces the queue length on an approach where traffic would not otherwise have sufficient gaps to enter the roundabout. The use of roundabout metering is limited in the US, but there are a few locations that have implemented metering. This synthesis reviews those locations and identifies the lessons learned from those metering experiences. STATE OF THE PRACTICE REVIEW The contact at each of these jurisdictions was asked for information about the intent, details, and outcomes of their roundabout metering experiences. The following sections identify that information for each jurisdiction. The four locations with permanent metered roundabouts are listed in chronological order, from the first to implemented metering to the last. The aerial photo of each roundabout is from Google Earth, and each represents the view from an altitude of about 2,500 ft. Photos of the roundabout metering signals are from Google Maps street view. The aerial and street view photographs represent conditions at a variety of dates and may not be an accurate representation of the current conditions. CLEARWATER, FLORIDA The first jurisdiction in the US to implement metering at a modern roundabout was Clearwater, Florida. The roundabout is shown in Figure 1 and is located at the intersection of Clearwater Memorial Highway (State Highway 60), Coronado Drive, and Mandalay Ave. This roundabout is located at the end of the causeway that connects the beach area to the mainland, making it the major access point for vehicular traffic from the mainland. On days with high tourist activity, westbound volumes on the causeway increased from around 33,000 vehicles per day to almost 60,000 vehicles per day. The roundabout was constructed in 1999 as a means of addressing congestion and safety at the entry point to the beach area. Nine individual intersections were replaced by a single roundabout. The roundabout metering was added after spring break in 2000. The metering was installed on the westbound Memorial Causeway approach because westbound traffic was so heavy during peak tourism times that both the Mandalay and Coronado approaches developed significant queues due to the lack of gaps in the circulating traffic stream.

115 Source: Google Earth Figure 1. Clearwater Metered Roundabout METERING INFRASTRUCTURE The metering installation today consists of pedestal traffic control signals on each side of the westbound Memorial Causeway approach just upstream of the East Short Drive intersection. The stop line for the metering signals is located approximately 280 ft upstream of the approach entry to the roundabout. There is a pedestrian crosswalk located on the near side of the intersection, which was not added until after the metering signal was installed. The metering signal operates in a normal steady green – steady yellow – steady red mode.

116 DECISION MAKING TO IMPLEMENT METERING As mentioned, the need for metering was identified as a result of heavy traffic when traffic from the causeway spiked, leading to significant queues on the other approaches to the roundabout (due to lack of gaps in the circulating traffic). The benefit of roundabout metering was evaluated by placing a police officer on the approach to the roundabout along with observers on hotel rooftops in the area who could communicate with the officer by radio to inform him when he should stop the westbound traffic to allow the approach queues to clear. This inexpensive experiment proved successful and led to full metering implementation. The metering signal rests in the green mode. When activated, the signal displays a steady red indication for about 90 seconds. Either a queue detector or a pedestrian pushbutton can activate the metering signal and change the display from green to yellow to red. Each mechanism is described below. As such, the metering signal serves two purposes: metering traffic entering the roundabout when activated by the queue detection and serving as a pedestrian signal when activated by the pushbutton. The measures below have been taken to ensure effective metering at this location. • Queue Detection: A detection zone on Mandalay Avenue detects when the queue on this approach reaches a critical threshold and activates the metering signal. The detection zone is located upstream of the pedestrian crosswalk and is approximately 400 ft from the entrance to the roundabout. • Pedestrian Pushbutton: There are two locations where a pedestrian can travel from one side of the causeway to the other. One is grade-separated from the causeway and is located on the bay side of the barrier island. The other is the pedestrian crosswalk at East Shore Drive. The crossing is controlled by signals in both directions on the causeway, with the westbound signal also serving as the metering signal for the roundabout when activated by the queue detector. • Emergency Preemption: A fire station is located about a half-mile north of the roundabout on Mandalay Avenue. When a fire truck needs to travel south on Mandalay Avenue, they activate the metering signal from the fire station. By the time the fire truck reaches the roundabout, any queue that was present has been cleared. LESSONS LEARNED AND FUTURE CONSIDERATIONS Clearwater’s contact offered the following suggestion: • If there is a possibility of needing a metering signal in the future, put in the conduit at the time of roundabout construction since it costs little to do so at the time of construction. Do not locate the conduit too close to the entry point to avoid approaching motorists confusing the green light for permission to ignore the Yield sign. PUBLICATIONS Specific details about the metering of this roundabout have been published in a paper (Sides 2020). COLUMBIA, MARYLAND The second jurisdiction to implement metering at a roundabout was the Maryland State Highway Administration (MDOT SHA). The roundabout is shown in Figure 2 and is located at the intersection of Maryland Highway 100 and Snowden River Parkway. This roundabout has some unique characteristics— as the state highway approach and departure to the roundabout are exit and entry ramps to a controlled-

117 access freeway (State Highway 100), and the Snowden River Parkway leg is only on one side of the roundabout, making it a T-intersection with only two approach legs. The other unique characteristic is that the Snowden River Parkway approach passes below the freeway, and the separating structure limits sight distance for the exit ramp from the freeway. The roundabout was constructed in 1998 as part of a new interchange, and the metering was added in 2007 due to queues on the exit ramp leg backing up onto the freeway. Source: Google Earth Figure 2. Columbia Metered Roundabout METERING INFRASTRUCTURE The metering signal consists of two horizontal, three-section traffic signal heads that are located within the roundabout. Each signal head displays a steady red, steady yellow, and flashing yellow indication. There is a queue detector on the exit ramp. The metering signal rests in a flashing yellow indication. When the queue detector on the exit ramp is activated, the signal indication changes in the following succession: rapid yellow flash – steady yellow – steady red. The approach to the metering signal includes advance signs. The Signal Ahead sign has flashing beacons above the sign that operate at all times, even when the metering signal is not operating. DECISION MAKING TO IMPLEMENT METERING There are only two approaches to this roundabout. One approach leg is an exit ramp from a freeway, and the other approach leg is the stem of the T-intersection and represents a major arterial. During the

118 evening peak, the arterial has high volumes entering the freeway. The arterial volumes entering the roundabout are high enough that there are not adequate gaps for vehicles on the approach leg exiting the freeway to enter the roundabout. When activated, the metering signal displays a red indication for 35 seconds to allow traffic on the exit ramp approach to enter the roundabout. In addition, sight distance for vehicles on the exit ramp is restricted until a vehicle is at the entrance to the roundabout, essentially requiring every vehicle to stop before entering the roundabout. LESSONS LEARNED AND FUTURE CONSIDERATIONS After gaining experience with the operation of the roundabout at this location, Columbia’s contact indicated that this location might have operated better as a stop-controlled intersection with only two approaches. PUBLISHED PAPERS There are no additional sources of information regarding metering at this roundabout. CARMEL, INDIANA Carmel, Indiana, is one of the country’s most roundabout-friendly communities and has constructed roundabouts throughout the jurisdiction. One is a dogbone-style roundabout located across one of the City’s freeways. The roundabout is shown in Figure 3 and is located at the intersection of E. Smokey Row Road and Keystone Parkway (the freeway). The roundabout was built around 2009, and metering signals were installed between 2016-2017 when upgrades to other roadways changed traffic patterns and increased volumes on Keystone Parkway. Source: Google Earth Figure 3. Carmel Metered Roundabout

119 One of the unique features of the metering at this roundabout is that one of the metering signals controls an approach that is within the dogbone portion of the roundabout that does not otherwise have to yield to traffic. Another unique feature is the high volume of school buses that travel from the west side of this dogbone and make a U-turn at the dogbone. METERING INFRASTRUCTURE This dogbone roundabout has metering signals on two approaches on the east side of the dogbone. One signal controls the northbound exit ramp from Keystone Parkway, and the other controls the eastbound approach on the same side of the dogbone. Of the four permanent roundabout metering locations the research team studied, this is the only one that uses a hybrid beacon to control traffic. Unless they are active, the beacons rest in dark. There are about 65 ft between the beacons on the approach and the roundabout. Carmel’s contact indicated that this created some initial confusion during the first weeks after the initial operation; however, there were no problems after that. The operation display is typical of a hybrid beacon: dark – flashing yellow – solid yellow – solid red – flashing red – back to dark. The solid red interval at this location lasts for 30 seconds. Once the beacon becomes active based on the presence of a queue, the metering signals operate for about 15-20 minutes before the queue dissipates. There is no provision for a pedestrian to activate the hybrid beacon from the adjacent crosswalk. The detection is achieved through a census puck embedded in the pavement. The closest is about 350 feet from the roundabout and there are two additional sensors further back on each approach. The metering is triggered when the furthest sensor detects a queue that has existed for a predetermined length of time. DECISION MAKING TO IMPLEMENT METERING The high volumes of traffic within the dogbone create queues on the westbound approach and northbound exit ramp. When a westbound queue is detected, both metering signals become active, which happens mostly during the morning peak. When a northbound exit ramp queue is detected, only the eastbound metering signal is active, which happens mostly during the afternoon peak. LESSONS LEARNED AND FUTURE CONSIDERATIONS The roundabout meters appear to have been an effective tool for addressing the temporary queues that form at this roundabout in the mornings and afternoons. The City of Carmel is happy with the results of the installation and plans to continue operating it in the current form. Carmel’s contact indicated that one possible issue with the metering signals on these two approaches is the proximity of the hybrid signals to the pedestrian crosswalk at the roundabout. The signals do not have pushbuttons and cannot be activated by pedestrians. There are also no stop lines at or near the locations of the hybrid metering signals. PUBLICATIONS No publications were identified. RICHLAND, WASHINGTON The most recent installation of a metering signal at a roundabout occurred in Richland, Washington, in November 2018. This roundabout is located along a freeway (State Highway 240), where the exit and entrance ramps intersect with Columbia Park Trail and North Steptoe Street. The roundabout is shown in Figure 4. The roundabout metering signal is installed on westbound Columbia Park Trail to create gaps for traffic on the exit ramp to enter the roundabout.

120 Figure 4. Richland Metered Roundabout Source: Google Earth METERING INFRASTRUCTURE The metering signal for this roundabout is located on the westbound approach of Columbia Park Trail. It is located about 250 ft from the roundabout entry and is designed to operate like a freeway ramp meter, displaying a green indication that is long enough for one vehicle to pass the signal. The signal is dark when it is not in active metering mode. The metering rate is around 6-to-11 vehicles per minute. In typical conditions, it is active from about 4:45 p.m. until 5:30 p.m. to 5:45 p.m. The signal is activated by queue detectors on the exit ramp that are located at 500 ft and 1,200 ft from the roundabout entry point. The metering mode is activated when occupancy at either loop exceeds 40% for three consecutive 20-second intervals. The metering option ceases after 15 minutes or when occupancy is less than 30% for three consecutive 20-second intervals, whichever is later. Once the metering operation stops, it stays off for at least 10 minutes. The metering mode is time-limited so that it can be activated only between 4:00-7:00 p.m. on weekdays. Since the metering signal is located on the far side of a freeway underpass, there is a warning sign with a flashing beacon on the near side of the underpass. The flashing beacon is active when the metering signal is operating.

121 DECISION MAKING TO IMPLEMENT METERING When the roundabout was originally built in 2007, it was a 2×2 roundabout. Some of the approaches were reduced to a single lane to reduce the occurrence of property damage only crashes. The resulting reduction in capacity and gap sizes on Columbia Park Trail caused traffic on the exit ramp to back up onto the freeway. The metering signal was installed on the high volume approach to allow the exit ramp to clear during the afternoon peak period. The metering signal has not been activated during 2020 COVID- 19 pandemic conditions due to lower traffic volumes. LESSONS LEARNED AND FUTURE CONSIDERATIONS Before the COVID-19 pandemic, the metering had solved the queue backup problem on the freeway. PUBLICATIONS No publications were identified.

122 8. Traffic Control Devices – Rail Crossing Synthesis Summary The national system of railroads largely pre-dated our national system of roadways. As our roadway network has grown, it has increased the interactions with the rail network. Where signalized intersections are located near a railroad grade crossing, traffic signal preemption is often used as a means to clear the queue over the grade crossing before the arrival of a train. However, when the intersection is a roundabout located near a grade crossing, there are no signals that can be used to apply the preemption concept and clear the queue unless signals are part of the roundabout design. This lack of preemption sometimes creates a reluctance to build a roundabout near a grade crossing or where a crossing goes through an intersection. Although limited, some roundabouts have been built at or near grade crossings, and a few of them are described in this synthesis. STATE OF THE PRACTICE REVIEW The state of the practice review included a review of existing guidelines from significant national and state resources for grade crossings in/near roundabouts as well as a review of control plus operations at selected locations where there is a grade crossing in or near a roundabout. The review included the following published documents: • NCHRP Report 672 - Roundabouts: An Informational Guide, Second Edition (Rodegerdts et al. 2010) • 2009 Manual on Uniform Traffic Control Devices (FHWA 2009) • Highway-Rail Crossing Handbook, 3rd Edition (Ogden and Cooper 2019) • State Design Manuals (WSDOT 2020; WisDOT 2020) • National Committee on Uniform Traffic Control Devices Draft Recommendation • Institute of Transportation Engineers Draft Recommended Practice (ITE 2006) Published guidelines for the design, control, and/or operations of grade crossings in or near a roundabout are limited. As indicated in the following documents, the general nature of the advice is to avoid placing grade crossings near roundabouts unless other options have been exhausted. NCHRP REPORT 672 - ROUNDABOUTS: AN INFORMATIONAL GUIDE, SECOND EDITION NCHRP Report 672, Roundabouts: An Informational Guide, Second Edition contains detailed information on roundabouts at or near a grade crossing, even though the specific design and control guidance is limited (Rodegerdts et al. 2010). It identifies that there are three common ways for a rail line to interact with a roundabout: • Within the roadway median and through the center of the roundabout. • Diagonally through the center of the roundabout. • Across one leg close to the roundabout. NCHRP Report 672 includes the following statements about these types of roundabouts: • Roundabout control options related to rail crossings include operating portions of the roundabout not affected by the rail crossing or closing the roundabout completely during rail events.

123 • Grade crossing treatments should follow criteria in the Manual on Uniform Traffic Control Devices (MUTCD) and those in the Railroad-Highway Grade Crossing Handbook (FHWA 2009; Ogden and Cooper 2019). • Issues to consider when designing such a crossing include, but are not limited to, the following: o Location of the crossing relative to the roundabout. o Traffic patterns and availability of queue storage. o The use of railroad gates versus highway signals. Railroad signals have a safe failure mode, where a loss of power drops the gate. Highway signals fail in flash or go dark. o Preemption sequence and timing, including queue clearance, train speed, and other factors. • A key consideration is the accommodation of vehicle queues to avoid queuing across the tracks. Traffic must not be forced to stop on the tracks. Where railroad gates are used to stop traffic, the gate placement and sequencing of the gates should be carefully considered to allow all exiting traffic to clear the tracks before the train arrives. 2009 MANUAL ON UNIFORM TRAFFIC CONTROL DEVICES The 2009 MUTCD expanded the treatment of traffic control at roundabouts, especially concerning pavement markings (FHWA 2009). One of the new sections (8C.12) addresses grade crossings within or close to circular intersections. This section requires that, where a roundabout or circular intersection is within 200 ft of a grade crossing, an engineering study must be conducted to determine if queuing could impact the grade crossing. If queuing is a factor, the engineering study serves to provide a means for clearing traffic from the crossing before the arrival of the train. Some of the actions that are listed in this section as a means of keeping traffic from queuing over the grade crossing include: • Eliminating the roundabout. • Revising the geometric design. • Adding grade crossing regulatory and warning devices. • Adding highway traffic signals. • Adding traffic metering devices, such as a metering signal. • Installing activated signs that display messages only when a train is present or coming. • Using a combination of these or other actions. The 2009 MUTCD also added a new traffic signal warrant (section 4C.10) to address intersections controlled by a Stop or Yield sign that are located within 140 ft of a grade crossing. Figure 1 provides one of several figures included in this warrant that help to define the need for further study of the value of installing a traffic signal. Some of these factors provide adjustment factors for the warrant, including rail traffic, buses, and tractor-trailer trucks.

124 Figure 1. Grade Crossing Traffic Signal Warrant HIGHWAY-RAIL CROSSING HANDBOOK, 3RD EDITION The Highway-Rail Crossing Handbook (Handbook) is one of the key references for the design and operation of rail grade crossings (Ogden and Cooper 2019). In 2019, FHWA published the third edition of the Handbook. The new edition does not address grade crossings near roundabouts in detail, but it does include the statement below. “Although roundabouts and traffic circles are designed to operate without traffic signals, they may become congested resulting in blockage of a crossing on an approach leg. Mitigation may require installation of a traffic control signal or queue cutter signal” (Ogden and Cooper 2019). A queue-cutter is a traffic control signal that only controls traffic approaching a crossing and is operated independently of other traffic signals in the vicinity. The concept of operation of a queue-cutter is to hold traffic (“cut the queue”) upstream from a crossing before a queue caused by a downstream traffic control signal or other roadway congestion can grow long enough to back up into the crossing. Queue-cutter signal operation may be based on downstream queue loop detectors, timed operations, or a combination of the two. STATE DESIGN MANUALS Generally, state-level resources provide limited guidance, and not all states provide guidance related to the topic. Two examples of state roadway design manuals that do address grade crossings near roundabouts include: • Washington State: “Although it is undesirable to locate any intersection near an at-grade railroad crossing, this situation exists at many locations on the highway system. Experience shows that a roundabout placed near a crossing has some operational advantages. If there is a railroad crossing near the roundabout contact HQ Traffic Office for further guidance” (WSDOT 2020). • Wisconsin: “Locating any intersection near an at-grade railroad crossing is generally discouraged. However, due to necessity, intersections are sometimes located near railroad grade crossings. When considering locating a roundabout within 1,000 feet of a railroad, contact the region railroad coordinator early in the process. It is preferable to cross one of the legs of a roundabout and leaving a typical distance of at least 100 feet from the center of the track to the yield line.

125 Treatment should follow the recommendations of the Wisconsin MUTCD whenever possible. Consider allowing the railroad track to pass directly through the circle center of the roundabout rather than through another portion of the circular roadway if the at-grade crossing is not on one of the legs. Also, consider the design year traffic on the roadway, the number of trains per day, speed of trains, length of trains, type of crossing warning devices, and anticipated length of vehicular queues when evaluating the intersection control needed in close proximity to the railroad. Expert assistance is required to address rail pre-emption requirements of roundabouts in close proximity” (WisDOT 2020). INSTITUTE OF TRANSPORTATION ENGINEERS DRAFT RECOMMENDED PRACTICE The Institute of Transportation Engineers (ITE) has a Recommended Practice (RP) on preemption of traffic signals near railroad crossings that was published in 2006 (ITE 2006). The 2006 document does not address roundabouts near grade crossings, but ITE is currently developing an updated version of this RP that includes content addressing this topic. The draft document includes a statement that references the 2009 MUTCD requirement to perform a traffic study if the grade crossing is within 200 ft of a roundabout. The draft also states that, if traffic queues impact the railroad crossing, provisions must be made to clear highway traffic from the railroad crossing before the arrival of rail traffic. REVIEW OF SELECTED EXISTING LOCATIONS In addition to a review of current guidelines, the research team identified locations around the US where a grade crossing was located in or near a roundabout. The complete list was evaluated by the team and narrowed down to a representative sample of locations that are described in this synthesis. For each location, the team identified the traffic control characteristics of the site using Google Earth and agency input, seeking input from an agency representative and/or a railroad representative on how well the roundabout or grade crossing functions. Unless indicated otherwise, all aerial and street view photos are from Google Earth or Google Maps. The locations are organized according to how the at-grade crossings are oriented relative to the roundabout, including: • At-grade crossing through the roundabout central island. • At-grade crossing on one leg near a roundabout. In addition to the locations described below, the team identified several other locations where there are grade crossings in or near a roundabout. The locations eventually included in the succeeding discussion were selected because they provide a representative range of the location types and treatments at which principles can be explored. AT-GRADE CROSSING THROUGH THE ROUNDABOUT CENTRAL ISLAND DAINGERFIELD, TEXAS (RAILROAD GRADE CROSSING) Daingerfield, Texas is a city of about 2,500 people located about 50 miles southwest of Texarkana, Texas. A single rail line of the Kansas City Southern Railway passes through the town. The railroad passes through the central island of a roundabout near the center of town at the intersection of Webb Street, N. Linda Drive, Jefferson Street, and Coffey Street, as shown in Figure 2. It is generally consistent with typical expectations except for the symbol sign that shows a railroad through the center island. This is a unique

126 sign that is not in the Texas or national MUTCD. There is no additional traffic control associated with the grade crossing at this location other than gate arms and railroad signals. Although located on city streets within Daingerfield, this project was funded and managed through the Texas Department of Transportation (TxDOT), with a consultant doing the design work. Communication with a local TxDOT district noted that the project was originally going to improve the existing grade crossing, but the design shifted to a roundabout during the design process due to indications of misdirected drivers with the prior grade crossing design. Discussions noted that the intersection functions much better now than it did before the roundabout was built, as it simplified the directional movements at the location. Additionally, communications noted that there have been no problems that TxDOT is aware of, likely because the site is at a low-volume location. Communication with a railroad industry vendor who works closely with various railroads noted that the railroad industry considers this an example of a successful location where a railroad line goes through the central island of a roundabout. Figure 2. Railroad Through Roundabout in Daingerfield, Texas Source: Google Earth

127 JENSEN BEACH, FLORIDA (RAILROAD GRADE CROSSING) Jensen Beach, Florida, is a city of about 11,000 people on the Atlantic coast near Port St. Lucie. Jensen Beach Boulevard connects US Highway 1 with the bay. A single-track railroad line parallels the coastline less than 1,000 ft from the water. This railroad line runs through the center of a roundabout on Jensen Beach Boulevard, as shown in Figure 3. The geometrics of this roundabout are interesting, as it has six legs. One of the Jensen Beach Boulevard legs has two approach and two departure lanes. The legs that parallel the railroad on the east side are a minor road and an alley. The roundabout has railroad gate arms and signals located only at the grade crossing. There is an Advance Railroad warning sign on one approach, but not on any of the other approaches. Three of the six approaches have RR markings on the approach. Figure 3. Railroad Through Roundabout in Jensen Beach, Florida Source: Google Earth The roundabout is located in Martin County. Communication with the County revealed the following: • There is a heavy movement from the northeast bound approach to the northwest bound approach (left turn through the roundabout, NE Jensen Beach Boulevard to NE Pineapple Avenue), as that is a primary route to the causeway that leads to the Atlantic coast beaches. • While this roundabout has six legs, the Jensen Beach Boulevard and Pineapple Avenue legs are the major ones. • The roundabout is a high-volume intersection, but there are seasonal variations in volume. • There is no additional traffic control beyond that identified above. • The County is generally satisfied with the location and feels that it works reasonably well. • There is not any traffic queuing into the grade crossing that the County is aware of. • There have been several rear-end crashes at the roundabout. Although this rail line is currently a single line freight rail, efforts are underway to expand it to a double line rail with freight and high-speed passenger trains. All of the individuals contacted about this location expressed concerns about the crossings in this context and suggested that improvements would likely be needed to accommodate the higher speed and increased number of trains. Trains coming from opposite

128 directions with little time between arrivals would create the potential for queuing over the tracks. The appropriate amount of warning time for the train is also an issue. SALT LAKE CITY, UTAH (LIGHT RAIL TRANSIT GRADE CROSSING) Salt Lake City is a major metropolitan area that serves as the capital of Utah and home to the University of Utah. There is a double-track light rail line on the south side of the university campus in the median of South Campus Drive. The light rail line goes through the center of a three-leg roundabout at the intersection with Campus Center Drive. All three roundabout legs are single lane entry and single lane exit. There is also a right-turn bypass lane for one of the legs. The grade crossings have railroad gate arms and signals at the crossing. In addition, this location has a railroad signal on the outside of the roundabout that is oriented to traffic within the roundabout. There are also railroad gate arms and signals that stop traffic on the roundabout approach on South Campus Drive (the road that parallels the light rail line). The approach that serves as the stem of the T has a STOP HERE FOR TRAIN sign below the Yield sign at the roundabout entry. The typical approach to the roundabout has an Advance Railroad warning sign with a Circular Intersection sign and EXEMPT sign below that. Figure 4. Railroad Through Roundabout in Salt Lake City, Utah Source: Google Earth The research team contacted the Utah Transit Authority, which is responsible for the light rail line, and discussed the intersection with five of their personnel. The most important point identified during the discussion was that, even with some of the challenges associated with a crossing through the center of the roundabout, agency representatives shared that the intersection functions much better now than it did before the roundabout was constructed. The roundabout resolved several flow issues and improved the overall safety of the intersection. One challenge of the current design is that a gate arm breaks about once a month (on average). The personnel the research team spoke with believed that the broken gates are typically the result of people trying to beat the gates when they start to come down. There have also been a few instances where large trucks have knocked out the entire gate arm assembly at one corner. The light rail at this location typically has three or four train cars and can occupy the crossing for 30-to-60 seconds. There have also been situations where a light rail train from the opposing direction will occupy the crossing as the previous train is leaving the crossing. Personnel indicated that the most problematic situation is when there is a short gap between opposing trains that allows traffic to start flowing into the

129 roundabout only to force it to stop again. One of the bigger challenges at this location is during special events, such as basketball games on the university campus. Under these conditions, they sometimes raise the gate arms for the eastbound and westbound traffic and use police officers to control traffic movement into the roundabout. Queues during special events can be long. The personnel from the Utah Transit Authority offered a few suggestions for improving the current location, which included: • A bypass lane for the westbound through movement would be helpful. • They are considering removing the gate arms on the eastbound and westbound approaches so that through traffic can move through the intersection during a train event. • A relief route at a nearby intersection could reduce demand at this roundabout. AT-GRADE CROSSING ON ONE LEG NEAR ROUNDABOUT NORTH OF FORT WORTH, TEXAS (RAILROAD CROSSING ON ONE LEG NEAR ROUNDABOUT) About 13 miles north of downtown Fort Worth, Texas is US Highway 81/287—a freeway that has a diamond interchange with Bonds Ranch Road and a roundabout on each side of the freeway. There is a BNSF double track railroad about 800 ft west of one of these roundabouts (Figure 5). The general area is suburban. There is no railroad-related traffic control in the roundabout nearest the railroad line or on the approaches to the roundabout. The grade crossing has an Advance Railroad warning sign, NO TRAIN HORN plaque, RR pavement markings, and railroad gate arm with railroad signals. Communications with the railroad industry indicated that queuing occurs during peak hours due to long freight trains at the grade crossing. Discussions also noted that the queue overloads the roundabouts. The queuing is mostly located from the roundabout back to the crossing and occurs because traffic exiting the freeway fills the roundabout so that traffic on the leg coming from the crossing does not have adequate gaps to enter the roundabout. Communication with the representatives noted that metering signals may be helpful to clear the queues. Discussions also suggested that a queue-cutter signal, which is a signal installed in advance of the grade crossing, might be needed to prevent traffic from queuing over the tracks. Figure 5. Railroad Crossing Near Roundabout North of Fort Worth, Texas Source: Google Earth KENNEWICK, WASHINGTON (RAILROAD CROSSING ON ONE LEG NEAR ROUNDABOUT) There is a four-leg roundabout about five miles west of Kennewick, Washington, that has a single railroad track crossing one of the legs, as shown in Figure 6. The roundabout is about 1,000 ft north of a partial cloverleaf interchange on Interstate 82. Each leg of the roundabout has a different roadway name (Leslie

130 Road., W. Clearwater Avenue, E. Badger Road, and Ridgeline Drive). The distance from the track to the roundabout entry is about 160 ft. All approaches to the roundabout have two lanes. The only railroad- related traffic control is on Leslie Road, which includes Advance Railroad warning signs, RR pavement markings, railroad gate arms with signals, and cantilever railroad signals. There does not appear to be any railroad-related traffic control in the roundabout or on the approaches to the roundabout. Figure 6. Railroad Crossing Near Roundabout near Kennewick, Washington Source: Google Earth A representative from the Washington State Department of Transportation (WSDOT), provided some information on the control and operations of this roundabout, including that: • The roundabout is off the state system and is the responsibility of the City of Richland. • There is no additional control at the roundabout that is related to the grade crossing. • The state is not aware of any queue or other operational issues associated with this roundabout. REEDLEY, CALIFORNIA (RAILROAD CROSSING ON ONE LEG NEAR ROUNDABOUT) In Reedley, California (a city with a population of about 24,000), a single-track railroad bisects a four-lane road (N. Reed Avenue) connecting a signalized intersection with a roundabout, as shown in Figure 7. The roundabout has three legs, and the roundabout entry on one leg is about 100 ft from the railroad track. The stop line for the signalized intersection is about 60 ft on the other side of the railroad. The railroad grade crossing has gate arms and railroad signals with cantilever signals and RR pavement markings. There are no Advance Railroad warning signs before the grade crossing. There are flashing red beacons near the crosswalk on the two legs of the roundabout that do not cross the tracks. These beacons are activated when the train preemption sequence begins and are intended to stop traffic before entering the roundabout. There is no crosswalk on the leg that crosses the railroad. There is a No Right Turn blankout sign for the northbound right-turn lane at the signalized intersection for the movement that crosses the track after turning right. Figure 7. Railroad Crossing Near Roundabout in Reedley, California

131 Source: Google Earth Communication with the City indicated that the City is happy with the roundabout installation. Before the roundabout construction (4-5 years ago), they had numerous crashes at the intersection but have not had any since it was built. MECCA, CALIFORNIA (RAILROAD CROSSING ON ONE LEG NEAR ROUNDABOUT) At the edge of the unincorporated area of Mecca, California, there is a T roundabout with one leg crossing a double-track railroad, although one of the tracks was installed for future expansion and does not extend much beyond the limits of the roadway. This location is similar to the Reedley location in that there is a T roundabout on one side of the railroad and a signalized intersection on the other side, although the separation distances are longer. Figure 8 shows the roundabout, crossing, and signalized intersection. The distance from the railroad to the roundabout entry is about 200 ft, and the distance to the signal is about 230 ft. All approaches to the roundabout are single lane, although there is a right-turn bypass lane for the approach that goes from the railroad to the roundabout. The approaches to the grade crossing have an Advance Railroad warning sign, RR pavement markings, and railroad gate arms with signals. The traffic signal has a preemption connection to the grade crossing. There is not any railroad-related traffic control on any of the approaches to the roundabout except for a 4×2-ft blankout changeable message sign on the two approaches to the roundabout. When the crossing preemption is activated, the blankout sign displays a graphic of a train with the legend USE ALT ROUTE. When not activated, it is sometimes used as a speed feedback sign.

132 Figure 8. Railroad Crossing Near Roundabout in Mecca, California Source: Google Earth Communication with the County revealed that the roundabout is the main way into and out of Mecca. As the town is small, the volumes through the roundabout are low. The right-turn bypass lane at the roundabout was included in the design because that is the predominant movement at the roundabout; it was not included as a queue reduction treatment related to the crossing. Discussions noted that there are no issues with traffic queuing over the tracks on the approach to the roundabout. A unique feature of this crossing is the Keep Clear Zone signs and markings at the grade crossing. Communication with the County indicated that the signs and markings were installed at the request of the railroad company and California Public Utilities Commission and was primarily related to the traffic signal as opposed to the roundabout. Similar signs and markings are installed in the opposite direction.

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