Simulation Study of Access Management at Modern Roundabouts Treatments of Pedestrian Crosswalks

way. Vehicles entering the roundabout must yield cautiously to ones already navigating the circulatory lane(s). The far-reaching appeal of roundabouts can be specifically ascribed to their substantiated safety benefits, strengthened circulation efficiency, decreased maintenance costs, and improved aesthetic effects (1). France, leading the world with roughly 15,000 modern roundabouts, has been constructing this type of traffic facility at a rate of 1,000 or so per year (2). The inventory in the United States, although rapidly expanding in recent years, remains relatively limited. As of 2010, an online database records over 1,000 modern roundabouts in active operation nationwide, in sharp contrast to over 40,000 in the rest of the world (3). Currently, a large number of roundabouts are under construction or in the planning phase in North America. The flourishing emergence of roundabouts has kindled a widespread debate in response to relevant roundabout studies over the pedestrian access issue (4). Ashmead et al. found that roundabouts create serious difficulties to the visually impaired, and Harkey and Carter revealed that crossing becomes increasingly difficult as the conflicting vehicle volume rises and that ensuring pedestrian-friendly accessibility is more challenging with multilane than single-lane facilities (5, 6). Guth et al. showed that the crosswalk segment on outbound lanes is more hazardous than that on inbound lanes (7 ). Williams and Levinson have pointed out that “safety, capacity, continuity and connectivity of the roadway network are key” in access management (8). Safety research shows a clear link between access design and crash rates, and access management has major concerns for the safety and mobility of a roadway system (9–12). The Access Management Manual prescribes major transportation actions that include multimodal streets with sidewalks and adequate pedestrian refuges, but it does not address the pedestrian access issue at roundabouts (13). In 2002, the U.S. Access Board published Draft Guidelines for Accessible Public Rights-of-Way, Roundabout, which proposes pedestrian signals at all roundabout crosswalks. In 2005, the Access Board released a revised draft to call for the provision of a “pedestrian-activated traffic signal . . . for each segment of the crosswalk” at multilane roundabouts to ensure safe access for visionimpaired pedestrians (14). Operationally, this provision interrupts the vehicular flow continuity that is intended in roundabout design. Another critical issue is the enhanced likelihood that the yielding queue will spill back into the circulatory lane(s), a problem identified by Inman and Davis for some signalized roundabouts (15). Although signals are in use at roundabout crosswalks in Europe, Australia, and South Africa, few roundabouts have been signalized for pedestrians in North America (16, 17). Two single-lane roundabouts were signalized at university campuses (the University of Utah in Salt Lake City and the University of North Carolina in Charlotte), and one double-lane roundabout was signalized (and then Simulation Study of Access Management at Modern Roundabouts Treatments of Pedestrian Crosswalks