pages: TransportationCommission/2021-01-27.pdf, 3
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TransportationCommission | 2021-01-27 | 3 | as using Rectangular Rapid Flashing Beacons. Research has found that the yielding rate is good for single lane roundabouts. The rates do go down with multiple lane roundabouts. Vice Chair Nachtigall asked if landscaping of roundabouts and the splitter islands might reduce the visibility of pedestrians. Ms. Ferguson responded that, as part of the roundabout design process, sight distances are measured to determine a landscaping plan including planting heights, or if no landscaping should be installed, to retain visibility. Commissioner Yuen asked if traffic circles have the same benefits as roundabouts, particularly since many Alameda intersections could not accommodate a modern roundabout. Ms. Ferguson responded that mini-roundabouts are encouraged by the Federal Highway Administration for safety. And, they can be safer than other intersection controls. The important design considerations are to slow vehicle speeds, and to make clear how bicyclists and pedestrians will navigate the mini-roundabout. The reduced number of conflict points still are realized with mini-roundabouts. Commissioner Weitze asked for information on the different types of accidents that occur at one lane, versus two lane roundabouts. Ms. Ferguson responded that both eliminate fatal and severe collisions. However, more side swipe collisions occur with multi-lane roundabouts as drivers change lanes in the roundabout. Commissioner Weitze asked if this increase in minor accidents is this more or less than one would see at an intersection with a traffic signal. Ms. Ferguson stated that it varies depending upon context and the design of the roundabout such as which lane the vehicles are in as they enter the intersection. Commissioner Weitze stated that he has heard people say that because roundabouts are unfamiliar to the public, they will be dangerous. He asked if this is true, and if the collisions reduce over time, as the community gets used to them. Ms. Ferguson stated that single-lane roundabouts are consistently safe over time, even if the road users are unfamiliar with them. Multi-lane roundabouts perform better when drivers are familiar with them. For example, in Bend, Oregon, they used many single-lane roundabouts successfully for many years. Then, with growth, they planned multi-lane roundabouts, and for this they did an extensive outreach and education effort. There is no research on changing collision rates as familiarity increases, however, anecdotally, if collisions start out higher, they reduce with familiarity. Commissioner Weitze asked if the City has accident history for the Bayport roundabouts. Transportation Commission Meeting Minutes - January 27, 2021 3 | TransportationCommission/2021-01-27.pdf |