Background and Summary of a Guide for Roundabouts (2023) / Chapter Skim
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Pages 73-135
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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)
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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)
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84 2018, sec.
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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.
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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 builtup area.
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87 4. MINI-ROUNDABOUT SYNTHESIS SUMMARY This synthesis summarizes mini-roundabout research findings.
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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)
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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.
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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.
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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.
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92 the roundabout. Communication with the County revealed that sight distance requirements should be studied further as they relate to mini-roundabouts.
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93 • There were low truck volumes. • There were no nearby commercial driveways.
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94 5. IN-SERVICE ASSESSMENT AND RETROFIT SYNTHESIS SUMMARY The roundabout practice has evolved to the extent of now having existing roundabouts to assess.
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95 possible adverse performance. This is a theoretical exercise, as actual design decision-making considerations cannot be known.
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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.
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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.
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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.
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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.
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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.
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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)
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102 MD 198 (Laurel Fort Meade Rd.) /MD 32 WB Ramps – Jessup, MD The issues associated with this roundabout (Figure 8)
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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.
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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.
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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.
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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.
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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.
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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.)
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109 MacArthur Boulevard (Route 28) /Connery Avenue/Sandwich Road (Route 28A)
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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)
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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.
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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.
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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)
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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.
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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.
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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)
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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.
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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.
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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.
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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.
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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.
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122 8. Traffic Control Devices – Rail Crossing Synthesis Summary The national system of railroads largely pre-dated our national system of roadways.
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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)
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124 Figure 1. Grade Crossing Traffic Signal Warrant HIGHWAY-RAIL CROSSING HANDBOOK, 3RD EDITION The Highway-Rail Crossing Handbook (Handbook)
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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.
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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.
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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.
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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.
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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.
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130 Road., W Clearwater Avenue, E
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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)
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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.
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133 REFERENCES American Association of State Highway and Transportation Officials (AASHTO)
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134 National Committee on Uniform Traffic Control Devices. Item 20B-RR-01 Grade Crossings Within or In Close Proximity to Circular Intersections, https://ncutcd.org/wpcontent/uploads/Sponsor%20Comments/2020B/20B-RR-01.pdf, (As of December 11, 2020)
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135 Schroeder, B., L Rodegerdts, P
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