Background and Summary of a Guide for Roundabouts (2023)

Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

5 Findings and Applications Findings from the following research activities are summarized in this chapter: • Literature Assembly • Survey of User Feedback • Designing for Trucks Research • Designing for Bicycles Research • Syntheses on Research Topics • Guide Development 3.1. LITERATURE ASSEMBLY The project team reviewed relevant literature, including national and state research and guidance documents, and other sources. The team considered the literature when conducting research and developing Guide content. Appendix A includes the Guide Bibliography. 3.2. SURVEY OF USER FEEDBACK The project team developed an electronic survey to gather input on the development of the Guide. Key results of the survey responses are summarized below. • Survey Responses - 63 people responded to at least a portion of the survey. The survey was composed of five open-ended questions and one space for additional comments or feedback. • Respondent Characteristics - Responses came from representatives of state DOTs (45%) and consultants (22%), with remaining responses from city, county, and federal agencies, as well as academic institutions. Respondents had more than 10 years of experience working on roundabouts (67%). • Use of Current National Roundabout Guidance - Responses indicated design guidance, general reference, resource to inform state or local guidance, resource for public or external education, operational analysis, and safety evaluation. • Use of Future Guide - Responses indicated respondents use design guidance as a general reference for public or external education, operational analysis, informing state or local guidance, design examples, and design flexibility. • Need for New/Updated Content - Responses indicated a desire for content related to bicycle and pedestrian design, examples of public/external education, truck and/or

6 oversized/overweight (OSOW) vehicle design, and multilane roundabout safety. Multiple responses indicated content within current national roundabout guidance should be expanded or updated to include recent research. Six respondents (14%) indicated further guidance on the design and accommodation of bicyclists and pedestrians to be important. • Most Important Content to Retain - Ten respondents (19%) indicated that all listed topics were important, rather than choosing from among them. Respondents listed geometric design and performance checks, more than listed any other topic, followed by safety analysis and horizontal alignment. • Least Important Content to Retain - When asked which topics were least important for inclusion, 16 respondents (33%) indicated that all topics were important for inclusion and did not list any topics. Selected topics for least important included maintenance, landscaping, and construction staging. Some of the key considerations from this survey include: • Design and operations resource. Most respondents indicated they use current national guidance as a resource for design, and several respondents consult national guidance for operational analysis. • Resource as a supplement to local guidance. Respondents indicated they consult national guidance on these topics as a supplement to local guidance, with many reporting they would expect to continue this practice. • The scope and coverage of the current guide is useful. Many respondents indicated each of the topics in the current guide were useful. • Education and public outreach. Respondents expressed interest in national guidance as an educational and public outreach resource. Many respondents use current guidance in stakeholder engagement. • Bicycle and pedestrian design and integration. Many respondents indicated current national guidance is missing guidance for bicyclists and pedestrians. • Design flexibility and examples. Many respondents mentioned one or both of these topics when asked what they would like to see in future guidance. Responses included a desire for an emphasis on flexibility in situations where the ideal scenario is not possible, and a desire to see more design examples. • Safety. Several respondents use existing national guidance and envision using a future guide as a reference for intersection safety evaluations. Responses included identifying safety benefits of roundabouts relative to other intersection forms and using safety performance prediction models.

7 • Safety at multilane roundabouts. Several respondents discussed multilane roundabout safety when asked what they believe is missing from current national guidance. Responses included a desire for better differentiation among various multilane roundabout designs and a desire for identified pedestrian treatments at multilane roundabouts. • Intersection control evaluation. Several respondents suggested incorporating intersection control evaluation policies. • Truck and/or Oversized/Overweight (OSOW) vehicle design. Respondents suggested incorporating recent research in truck and OSOW design. Many respondents noted design impacts to use cases (Case 1, 2, and 3). • Improve existing roundabouts. Several respondents requested direction for retrofits to existing roundabouts and circular intersections. • Traffic control devices. Several respondents noted traffic control device sections were important or needed updates. 3.3. DESIGNING FOR TRUCKS The Designing for Trucks Research consisted of the following activities. Additional details from the research findings are shown in Appendix B. • State of the Practice Review; • Truck Industry Outreach; and • Driver Behavior Video Data Collection The research assessed roundabout design decisions for serving large trucks, specifically with respect to using truck cases to determine the design approach. For agencies and designers to achieve the desired performance, they must be able to understand the benefits and drawbacks of desired approaches and be able to evaluate their decisions. The Case 2 and Case 3 design approaches are still emerging, and there are too few years of historical, nationwide performance for these designs to have a comparative answer. However, the research tasks conducted for this project have yielded useful findings related to truck cases. The findings above confirm that information about Case 2 and 3 roundabouts is not consistent or well understood. Driver knowledge and expectations are not clear, and observed behavior confirms that behavior is not consistent. The Joint Truck Study by the Minnesota and Wisconsin Departments of Transportation (MnDOT and WisDOT) included many potential tradeoffs for Case 2 and 3 design types, but the potential benefits of Case 2 and 3 designs are unproven (MnDOT and WisDOT 2012). However, the challenges in designing roundabouts that meet the Case 2 and 3 design intent are known and can be evaluated with existing and emerging performance measures. The research indicated that agencies can weigh the potential benefits of new and different truck cases versus the known and quantifiable drawbacks.

8 DEFINITION AND APPROACH In the State of the Practice Review, the research team reviewed guidance about truck design to document the various approaches being taken by representative agencies. This included: • Massachusetts Department of Transportation (MassDOT), Guidelines for the Planning and Design of Roundabouts (MassDOT 2020) • Georgia Department of Transportation (GDOT), Design Policy Manual (Rev 6.0, June 6, 2020), Chapter 8: Roundabouts (GDOT 2020) • GDOT, Roundabout Design Guide (GDOT 2019) • Washington State Department of Transportation (WSDOT), Design Manual, Chapter 1320: Roundabouts (WSDOT 2017) • California Department of Transportation (Caltrans), Highway Design Manual, Seventh Edition, Chapter 400: Intersections at Grade (Caltrans 2017) • WisDOT, Facilities Development Manual (WisDOT 2016) • Kansas Department of Transportation (KDOT), Kansas Roundabout Guide, Second Edition (KDOT 2014) • Maryland Department of Transportation (MDOT), State Highway Administration (SHA), Roundabout Design Guidelines (MDOT SHA 2012) • Oregon Department of Transportation (ODOT), Highway Design Manual (ODOT 2012) Of the eight agencies surveyed, three (Massachusetts, Georgia, and Wisconsin) explicitly defined and discussed the truck cases. The definitions had subtle distinctions among them, including two different types of Case 2 roundabouts in Georgia’s guidance. Definitions vary regarding whether the intent of a Case 3 roundabout is simply for a truck to be able to traverse the roundabout within their lane or whether the design intent is to allow two trucks to traverse the roundabout side-by-side, even as they may encroach into the adjacent lane or a vane island. Some states have laws that govern the trucks’ ability to encroach on adjacent lanes within a roundabout as well as passenger car drivers’ ability to circulate next to trucks. This task revealed variance among states in documented design approach and the legal environment for drivers in roundabouts. UNDERSTANDING The research found several barriers to understanding driver comprehension and expectations: • The inconsistent definition described above presents a challenge for developing national guidance, but it also may present a challenge to truck drivers, many of whom have jobs that require interstate travel. Differences in design intent and definition across jurisdictions along with inconsistent use of traffic control devices to communicate the design intent to drivers make this largely unknown concept challenging for drivers to comprehend.

9 • As part of the truck industry outreach, the research team interviewed trucking industry representatives. Interview subjects were not familiar with truck cases and expressed doubt that drivers know of the concept. Some interview subjects shared a wholesale lack of truck driver education regarding roundabouts, leaving them to determine their own personal best practices or to learn informally. • Truck case design is difficult to determine visually. While several guides include key dimensions, the intended truck design case for a built roundabout can be difficult to assess—even when viewed from a scaled aerial—without validating truck turning paths using software. The striped vane island could provide a cue to drivers that they may be at a Case 2 or 3 roundabout, but a lack of visual cues in the circulatory roadway hinders a driver’s ability to assess the intersection. Given that striped vane islands in other contexts are not intended to be traversed (e.g., a freeway off-ramp gore area), the use of striped vane islands may not adequately communicate design intent to drivers. • As part of the driver behavior video data collection, the video observations of Case 2 designs revealed that truck driver behavior is not consistent or easily predicted. At observed Case 2 sites, nearly one-third of truck drivers did not stay in their lane at Case 2 roundabout approaches, a behavior that did not appear sensitive to the presence of adjacent traffic. Within the circulatory roadway, truck driver behavior did appear to be related to the presence and behavior of adjacent passenger vehicles: a majority (56%) of truck drivers in observed Case 3 roundabouts encroached on the adjacent lane contrary to the design intent. Truck driver lane discipline within the circulatory roadway is approximately 10% higher in the presence of adjacent traffic than without it. EMERGING OBSTACLES TO CASE 2 AND CASE 3 DESIGNS Using truck cases as a design approach has emerged in the last decade and has varied in implementation speed and approach across states. Recent legislation in at least three states has amended state vehicle codes to legally allow for Case 1 behavior. The vehicle code in Wisconsin (Wis. Stat. § 346.18 (2021)), Oregon (Or. Rev. Stat. § 811.292 (2022)), and Washington (Wash. Rev. Code § 46.61.140 (2021)) allow truck drivers to straddle lanes when navigating a roundabout; Wisconsin and Oregon codes also require other drivers to give way to trucks as they navigate. These legal changes put expected truck driver behavior in direct conflict with the Case 2 and Case 3 approaches; a truck driver familiar with the vehicle code would expect to be able to encroach on an adjacent lane at a roundabout rather than to stay in lane. SAFETY EVIDENCE MAY SUPPORT CASE 1 OR 2 DESIGN Because there are so few Case 3 roundabouts in operation, a full comparative safety evaluation is not possible and was not included in the research. However, this research examined collision data provided by WisDOT and found higher collision rates, normalized by volume, among Case 3 roundabouts compared to Case 1 and Case 2 roundabouts to date. These results have not been statistically validated and are intended as informational only.

10 3.4. DESIGNING FOR BICYCLES The Designing for Bicycles Research provided an overview of the bicycle facility design guidance and identified design strategies applicable to roundabouts that are appropriate for the person who is “interested but concerned” in bicycling. This included the following activities and additional details from the research findings are shown in Appendix B. • State of the Practice Review • Development of Treatment Concepts PRINCIPLES FOR DESIGNING FOR PEOPLE BIKING The publication review helped identify a list of principles related to designing roundabouts for people biking, specifically people “interested but concerned” in biking. • Minimize exposure to conflicts. • Reduce speeds at conflict points. • Clearly define areas of potential conflict. • Separate modes. • Clearly communicate right-of-way priority. • Provide predictable, simple, direct alignments. • Provide adequate sight distance. • Provide comfortable spaces for waiting and decision making. • Minimize person delay. DESIGN STRATEGIES Through the literature review; review of agency policies, guidance, and practices; virtual field review of ten sites; and feedback on the treatment concepts, the following are design strategies for people biking at roundabouts that are consistent with the identified design principles. These design strategies have been grouped by design element. General • In areas with heavy bicycle and pedestrian activity, the roundabout design should prioritize people walking and biking over other needs, such as accommodating large vehicles on all movements rather than specific movements where large vehicle movements are typical. This could include the use of a smaller inscribed circle diameter on roadways with operating speeds already below desired entry speeds to be able to include a separated bicycle facility at the roundabout. • In areas with heavy bicycle and pedestrian activity, a right-turn bypass lane should be used with caution. The entries and exits to and from the bypass lane can increase conflicts with bicyclists and with merging maneuvers on the downstream leg.

11 • In locations with existing operating speeds below 25 mph for single-lane roundabouts and below 30 mph for multilane roundabouts, fewer advanced speed control measures are necessary. Signs and Pavement Markings • In situations where roundabouts do not have separated facilities (either one- or two-way cycle tracks or shared-used paths), consider using sharrows to encourage people biking to ride in the middle of the lane. • Consider providing “Bikes May Use Full Lane” and/or “Do Not Pass Bikes” signs in locations where people biking are expected to circulate with traffic. Crossings • Provide raised pedestrian crossings to encourage people driving to yield to people walking and biking and to encourage slow vehicle speeds. • Raised pedestrian crossings across bicycle facilities could help encourage people biking to yield to people walking. • Crossings should be set back 20-to-25 ft on roundabout entries or single-lane exits and 50-to-75 ft on two-lane exits. • When the entry and exit crossing setbacks are not the same, a separated bicycle crossing should be provided. This helps reduce conflicts between modes, allows for using sharper angles at pedestrian crossings for pedestrians with vision disabilities and avoids navigation challenges for people biking at bicycle crossings. • Locating bicycle crossings on the outside of pedestrian crossings provides additional room for vehicles to yield, minimizes pedestrian travel distances, and provides greater separation from the circulatory roadway on the exit. • In constrained locations where users must share the same space because separate bicycle and pedestrian crossings are not possible, provide a wider crossing (15 ft is preferred). • When a separated bike crossing or a wider crossing with a mix of people walking and biking is provided, the use of a wider splitter island (10 ft or more) is preferred to provide additional bicycle storage and more space for users to wait. • Adequate sight distance needs to be provided at crossings to ensure people driving vehicles exiting the roundabout and people biking approaching the crossing should be able to clearly see each other through the recognition, decision, and yield/stop zones. • The separated bike lane approach to the bicycle crossing should result in bicyclists arriving at the queuing area at a perpendicular angle to approaching motorists.

12 Transitions • When transitioning from on-street bicycle facilities to separated bicycle lanes or a shared-use path, consider locating the dashed striping farther upstream to separate decision making and further clarify the transition area. Shared-Use Path Design • Users should be aware of mixing zones and of the speed differential between modes minimized. • For a series of closely-spaced roundabouts, extend the shared-use path from the first bicycle exit ramp to the last bicycle entrance ramp, allowing for people biking to leave the roadway and travel through all roundabouts on the shared-use path. Do not provide entrance ramps for bicyclists to re-enter the roadway between closely-spaced roundabouts (1,000 ft or less between roundabout centers). Provide exit ramps from the roadway to the shared-use path prior to the approaching roundabout. Separated Bike Lane Design • Provide separated facilities when bike or pedestrian activity is high enough to regularly require people walking and biking to share the same space. • Provide a “raised element” or “wayfinding buffer” between modes that is detectable underfoot. The buffer should be distinguishable from the walking area underfoot through texture and color contrast. • Within the location between the entry and exit pedestrian crossing, a 2-ft minimum buffer should be provided between the sidewalk and separated bicycle facility to minimize the potential for a pedestrian with vision disabilities to inadvertently step into the bicycle facility. FACILITY IDENTIFICATION Bicycle and pedestrian facilities at a roundabout should be integrated into both the existing and future surrounding pedestrian and bicycle network. For people biking, the bicycle facilities provided at the roundabout should match or exceed the bicycle level of the approaches, both when the roundabout is opened and under planned future facilities on approach roadways. 3.5. SYNTHESIS SUMMARIES The research team prepared synthesis summaries of the following eight topics. • Designing for OSOW Trucks • In-Service Assessment and Retrofit • Mini-Roundabouts • Economic Impact of Roundabouts

13 • TCD - Metering • TCD – Pedestrian crossings • TCD – Railroad crossings • Illumination The summaries are presented in Appendix C. The following sections summarize the key findings for each topic. DESIGNING FOR OVERSIZED/OVERWEIGHT TRUCKS This summary described how roundabouts can address various truck capabilities and how Oversize/Overweight highway trucks (OSOWs) can be accommodated via horizontal, vertical, and cross-section design. 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. Generally, states do not have substantial published guidance for OSOW accommodation at roundabouts. In practice, states evaluate accommodations on a case-by-case basis. Communication with Wisconsin Department of Transportation (WisDOT) revealed that if there is adequate communication with area stakeholders and OSOW haulers, then locations are typically not excluded from roundabout use due to OSOW requirements. Discussions with Oregon Department of Transportation (ODOT) revealed that communication includes elements such as route mobility, design vehicle exceptions, over-dimension vehicle to be accommodated, and typical design elements for any proposed roundabout on the state highway system IN-SERVICE ASSESSMENT AND RETROFITS OF EXISTING ROUNDABOUTS This summary established a framework for assessing existing roundabouts and identified methods to consider potential remediation approaches based on in-service performance. The summary also provided information about how roundabout design principles can apply to rotaries and other circular intersections for possible retrofit strategies. Information about the performance checks, contributing factors to undesirable performance, and typical retrofit modifications that may help to meet performance checks were summarized. 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 (e.g., skewed intersections) that contribute to fastest path and view angle challenges. When conducting in-service roundabout reviews, understanding factors that could contribute to undesirable performance and performing 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 target performance cannot be fully

14 attained, a roundabout retrofit is often the appropriate intersection form because of its beneficial safety and operational performance. MINI-ROUNDABOUTS This synthesis summarized mini-roundabouts 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 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. 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 They require less right-of-way. o They reduce installation costs. • 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 drivers’, and potentially truck drivers’, comfort and ability to operate a bus through a mini-roundabout can improve 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. ECONOMIC IMPACTS OF ROUNDABOUTS Information on the economic impacts of roundabouts could expand the planning considerations of intersection control evaluations and advance the roundabout practice. This summary provided information on roundabouts’ economic impacts on businesses, including documents and anecdotal information from jurisdictions that have implemented and invested in roundabouts on commercial corridors. The synthesis considers economic factors for their potential to augment other roundabout performance metrics, such as safety, operational performance, construction cost, and long-term

15 maintenance. The impacts roundabouts may have on businesses and local economies are not well-documented and, therefore, difficult to objectively evaluate. The key findings from the state of the practice review include the following: • Benefits related to safety, operational performance, and construction and maintenance costs were the largest economic considerations when considering roundabouts. • Reduced delay, stopping, and queueing are key factors in attracting the public and businesses to corridors where they had installed roundabouts. This finding was not directly related to roundabouts v. signals; instead, it was related to the roundabouts providing better traffic operations compared to traffic signals. • Benefits of bicycle and pedestrian user comfort at roundabouts. TRAFFIC CONTROL DEVICES – METERING One advantage of 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 to a roundabout can improve the roundabout’s operations. Providing signal control at one or more approaches to a roundabout is referred to as roundabout metering, which 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 improve performance by providing one or both of the following benefits: • Stopping traffic on one approach creates gaps in the circulating traffic that allow 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. Roundabout metering is limited in the US, but some locations have implemented it. This synthesis reviews those locations and identifies the lessons learned from those metering experiences. Based on the review of experiences at four installations with permanent roundabout metering as well as the other two locations (one with temporary roundabout metering and the other with freeway ramp metering on a roundabout approach), the following roundabout metering signal findings are offered: • Roundabout metering signals have been successfully used to create gaps in the roundabout circulating traffic so vehicles can enter the roundabout from approaches other than the high-volume approach. • Roundabout metering signals have operated only when queues on one or more legs of the roundabout create an operational and/or safety issue.

16 • Roundabout metering signals have most often been used where one of the legs of the roundabout is a freeway exit ramp and queues from the roundabout extend back onto the freeway. They have been successful at limiting the encroachment of the exit ramp queues onto the freeway. • The distance between the signal and the roundabout entry varies between locations. There is not sufficient data or experience to judge a minimum separation distance for use in guidelines. TRAFFIC CONTROL DEVICES – PEDESTRIAN CROSSINGS This summary included a state of the practice review that summarizes the findings and policies from the following documents: • NCHRP Report 834, Crossing Solutions at Roundabouts and Channelized Turn Lanes for Pedestrians with Vision Disabilities (2016). • NCHRP Web-Only Document (WOD) 222, Guidelines for the Application of Crossing Solutions at Roundabouts and Channelized Turn Lanes for Pedestrians with Vision Disabilities (including Appendices C and D, Revised Chapters 6 and 7, respectively) (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 (the applicable report from FHWA TOPR 34) (2015). NCHRP Report 834 The review of NCHRP Report 834 found the following: • Issues and Principles of Wayfinding at Intersections: The report describes the four-step task pedestrians with limited visibility use when crossing a street and contains examples of wayfinding errors that can be encountered at roundabouts. The crossing framework provides a new method to assess pedestrian crossings. • Determining the Appropriate Crossing Location: The report provides insight into considerations for curb ramps, detectable warnings, and path alignment for pedestrians who are blind as they approach a crosswalk. It also offers examples of treatments that provide varying degrees of wayfinding support. • Aligning to Cross and Establishing the Correct Heading: The report contains details on considerations for techniques used in the actual crossing maneuver, with additional descriptions of cues used to begin the crossing and how ramps and detectable warnings are incorporated into those decisions. • Issues and Principles for Determining When to Cross: The report provides details that further complement the four-step crossing concept introduced previously.

17 • Crosswalk Location and Angle Options: The report provides detail on the competing challenges of locating crosswalks and options for crosswalk alignment at roundabouts. • Buffering: The report provides details on separation treatments (i.e., landscaping, fencing, and bollards). • Type of Traffic Control Device: The report describes the categories of devices (i.e., traffic signal, PHB, and RFB). It has current information on RRFBs. • Location of Signal/Beacon Faces and Accessible Pedestrian Signals: The report provides current information on the location of the equipment. • Wayfinding Assessment: Provides detailed methodology for evaluating a crosswalk or crossing location from the perspective of a pedestrian who is blind or has low vision. • Crossing Assessment: Provides a detailed methodology for evaluating the entire crossing maneuver in an existing or proposed design (Schroeder, et al. 2016). NCHRP Web-Only Document 222 Much of the material in WOD 222 is also found in NCHRP Report 834. The discussion of exit radii in the conclusions and findings (Chapter 6 of WOD 222) is useful for describing real-world applications of design decisions (NCHRP 2016). FHWA Report FHWA-SA-15-069 This report presents results from a pedestrian accessibility study evaluating the effectiveness of RRFBs at multilane roundabouts in the United States (FHWA 2015). The findings from this study form the basis for some of the guidelines and recommendations found in NCHRP Report 834 (Schroeder et al. 2016) and WOD 222 (NCHRP 2016). As such, these are generally incorporated into the findings, suggestions, and recommendations described above (Schroeder et al. 2015). TRAFFIC CONTROL DEVICES - RAILROAD CROSSINGS The research team reviewed existing guidelines that address the presence of a grade crossing in or near a roundabout, which included identifying current efforts to improve such guidelines. The research team also identified several existing roundabouts located where there is a railroad or light rail-grade crossing in or near the roundabout. The team documented the conditions for these locations and reached out to various stakeholders (agency and/or railroad practitioners) for information about the sites to learn about the control and operations at the locations. Elements Unique to Roundabouts The primary concern regarding roundabouts is the queueing that can occur at the roundabout entry and extend back through the grade crossing. There are also concerns that pedestrians, parking on the departure, or other factors on a roundabout departure can create a queue in the roundabout that may block a grade crossing. Unlike signalized intersections, most roundabouts do not have an innate option for clearing the queue on a roundabout approach before the arrival of a train. Without the ability to “flush” or

18 clear the queue on an approach to a roundabout, traffic can be occupying a grade crossing when the train arrives. Existing Guidance The current guidelines for design and control of roundabouts and grade crossings that overlap or are close together are limited but include some key themes: • NCHRP Report 672 provides the most extensive treatment of the topic, but even that is limited in its level of design and control guidance (Rodegerdts et al. 2010). • The Manual on Uniform Traffic Control Devices (MUTCD) establishes requirements for traffic control devices at both crossings and roundabouts that must be met, but it does not provide specificities about when the two features overlap or are close together (FHWA 2009). • The Highway-Railroad Crossing Handbook indicates that queue-cutter signals may be a traffic control treatment that deserves consideration near grade crossings when there is potential for the queue from a roundabout to extend into the crossing (USDOT, FHWA/Federal Railroad Administration (FRA) 2019). Factors to Consider Key findings related to influencing factors include the following: • Grade crossings that are up to a quarter-mile from a roundabout can impact queueing within the roundabout. • Concerns regarding grade crossings near roundabouts is the queue from a crossing extending back into the roundabout and creating a gridlock condition in the roundabout. The length of a queue created by a train at a grade crossing can be impacted by many factors, including: o Length of the train. Some trains can exceed 10,000 ft in length, and such lengths are likely to become commonplace in the future. o Speed of the train. Communities that have established lower train speeds create longer queues at grade crossings. High-speed trains create the need for long advance warning times. o Frequency of train arrivals. Where crossings serve light rail or other transit vehicles, frequent train arrivals may perpetuate queues. o Conflicting approach traffic. Where conflicting approach traffic is highly peaked or serves comparatively high volume (e.g., related to special events or freeway off-ramps), queues may be highly variable. • The complications of a grade crossing in or near a roundabout are lessened when roundabout traffic volumes are low.

19 • Double-rail lines have a higher potential for a queueing condition over the tracks when traffic is clearing after a first train with a second train arriving shortly after. Solutions There are a variety of treatments to address queueing when there is a grade crossing in or near a roundabout. • Some existing roundabouts have used some form of signal or beacons to create a stop condition when a train is approaching a grade crossing on the roundabout entries that do not cross the tracks. By stopping the traffic on the approaches not crossing the tracks, on the approach crossing the tracks can enter the roundabout and clear the crossing. This approach is similar in concept to roundabout metering. • Some roundabouts have used railroad gate arms on approaches to essentially close the roundabout to traffic when a train is nearing or is present at the crossing. Closing the roundabout to all traffic during train passage is practical for light rail crossings where the train is short and occupies the crossing for a short time. • A right-turn bypass lane for the approach crossing the tracks can reduce the potential for queueing over the railroad tracks. ILLUMINATION This summary included recent research findings on roundabout lighting, with a particular focus on ways to increasing lighting design flexibility without sacrificing its core safety intent. The purpose of lighting is twofold: to make the intersection visible from a distance and to make key conflict areas visible (Illuminating Engineering Society of North America (IES) 2018; NCHRP 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, and unexpected fixed objects or animals may be in travel lanes. Intersection lighting increases visibility. IES notes 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). While lighting roundabouts provides visibility and reduces crash risk, lighting adds cost and can reduce implementation feasibility. In rural areas, costs of lighting include equipment and installation at the intersection, itself, as well as the cost of providing power where no supply is nearby. Lighting operation and maintenance costs come from different budgets than the initial capital investment, and these costs may be the responsibility of local agencies rather than the agency who funded the original capital improvement. Solar-powered lighting can reduce the need for an external power supply but 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.

20 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 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. • The 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, section 12.4.4). • AASHTO Roadway Lighting Design Guide, Seventh Edition (AASHTO 2018), and ANSI/IES Recommended Practice for Design and Maintenance of Roadway and Parking Facility Lighting, RP-8-18 (ANSI/IES 2018), identify transition lighting minimums that are not sensitive to factors like exit speed and geometry. • Lighting guidance could be flexible, and parallels can be drawn to transition lighting at tunnels, toll plazas, and rest areas. • PennDOT’s lighting policies (Rodegerdts and Myers 2020) 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). • GDOT’s Evaluation of Current Practice for Illumination at Roundabouts (Rodgers et al. 2016) 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. 3.6. GUIDE DEVELOPMENT The research team developed the Guide, which serves as the primary source for guidance on all aspects of roundabouts. With a continued focus on flexible, multimodal design in transportation planning and design, the Guide expands performance-based decision making to better account for vulnerable users and adapt roundabouts to all contextual environments. Integrating research findings from state and national guidance, and other sources, the Guide draws upon broad transportation planning and design guidance from outside the roundabout practice area. This includes concepts such as project type (new versus reconstruction) and context classification that expands design flexibility beyond focusing on functional classification.