Background and Summary of a Guide for Roundabouts (2023) / Chapter Skim
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From page 5... ...
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.
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6 oversized/overweight (OSOW) vehicle design, and multilane roundabout safety.
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7 • Safety at multilane roundabouts. Several respondents discussed multilane roundabout safety when asked what they believe is missing from current national guidance.
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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)
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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.
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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.
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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)
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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.
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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.
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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.
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15 maintenance. The impacts roundabouts may have on businesses and local economies are not well-documented and, therefore, difficult to objectively evaluate.
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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.
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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)
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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.
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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.
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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.
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