Estimating Speeds at High Speed Rural Roundabouts

This paper investigates the relationship between American roundabout geometric design elements and driver selected speeds. From May to August of 2003, an extensive data collection effort was undertaken as part of the National Cooperative Highway Research Program (NCHRP) Project 3-65 to obtain spot speeds and roundabout geometric design information for 32 roundabouts located in 11 States. This study utilizes a portion of this dataset by testing 11 single-lane roundabouts which include a total of 40 roundabout approaches. These roundabouts were chosen for their placement in potentially high-speed environments. Fourteen simple linear regression equations were developed to estimate the differential in speeds at several key locations including the merge area of entering/circulating vehicles. These models may be used to gain insight into how roundabout design may affect the driver selected speeds which in turn influence safety and operational performance.