Hillsborough County Complete Streets Guide

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Elements of Complete Streets

ROUNDABOUT A roundabout is a type of round intersection or junction in which road traffic is permitted to flow in one direction around a central island and priority is typically given to traffic already in the junction. Roundabouts reduce the likelihood and severity of collisions greatly by reducing traffic speeds and minimizing right angle and head on collisions. Roundabouts provide significant benefits for all road users by reducing the number of conflict points that can occur when compared to a signalized or unsignalized intersection. 15 Figure 2-12 demonstrates how vehicular conflicts are reduced from thirty-two to eight points while eliminating crossing conflicts, which are the main cause of serious injuries and fatalities. According to the Highway Safety Manual, this has been found to increase overall safety for roadway users by reducing the number of serious injuries and fatalities by 79% when compared to a signalized intersection. 16 Although the number of conflicts increases at multilane roundabouts when compared to single-lane roundabouts, the overall severity (and often number) of conflicts is typically less than other intersection alternatives.

Figure 2-12 Roundabout Vehicle Conflict Points (NCHRP)

Figure 2-13 shows roundabouts have 50% fewer pedestrian-vehicle conflict points than a comparable stop or signal-controlled intersection. Pedestrians cross a shorter distance of only one direction of traffic at a time since the entering and exiting flows are separated. Lower speeds in a roundabout, deliver better yielding rates, reduced vehicle stopping distances, and lower risk of collision injury or fatality 17 . Where bicycle facilities lead to a roundabout, a bicyclist should be given the option to either ride in the travel lane or use a ramp to and from a separated shared use path. Normal travel speeds through a roundabout are in the 15-20 MPH range. A roundabout can be used at intersections with high volumes of large trucks and buses, depending on design. They are

15 NCHRP Report 672 – Roundabouts: An Informational Guide – Second Edition, 2010 16 Crash Modification Factors Clearinghouse http://www.cmfclearinghouse.org/detail.cfm?facid=4184 17 FHWA, Roundabouts with Pedestrians and Bicycles https://safety.fhwa.dot.gov/intersection/roundabouts/fhwasa15016.pdf

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