S. Raza, A. Al-Kaisy, S. Washburn

Pages: 21-38

Abstract
Understanding the influence of roundabouts on operating speeds along connecting roadway segments is important for developing facility-level operational analyses along highway corridors and in modeling speed deceleration and acceleration in microscopic simulation. This study aims to investigate the influence area of roundabouts along rural and suburban corridors that would assist in determining the quality of traffic operations along highways involving roundabouts. The study used speed data collected via multiple test car runs along three roundabout corridors: two in the state of Washington and one in Colorado. Drivers’ speed profiles while driving through the roundabout corridors were established and analyzed. Furthermore, statistical analyses were conducted to model the upstream and downstream influence areas at the three study sites and in testing the effect of traffic volume and posted speed limit on the influence area. Study results suggest that the downstream influence area is significantly longer than the upstream influence area. Traffic flow level was found to have no significant effect on the roundabout influence area; however, the posted speed limit was found to significantly affect the upstream and downstream roundabout influence areas. The study results provided important information about the spatial extent of the operational effect of roundabouts on connecting approaches. However, these results are specifically derived using rural and suburban corridors and therefore may not be applicable to lower-speed urban environments.
Keywords: influence area; roundabout corridors; speed profile; quantile regression; facility segmentation