Appropriate deceleration on approaches to roundabouts is primarily accomplished through the use of applicable geometric design principles; however; traffic control devices (specifically signing and markings on the approach) also serve a vital role in communicating to the approaching driver what speed profile should be anticipated. This report provides a resource for engineers to identify and select appropriate speed-reduction treatments for high-speed approaches to roundabouts. The research examines best practices and research literature on speed-reduction techniques for high-speed approaches for all intersection types; as well as treatments for work zones and horizontal curves. Based on the findings from these efforts; the report summarizes a selection of treatments including traditional signs with and without beacons; pavement markings; illumination; speed-activated signs; and transition zones. Information on the effectiveness of these treatments; as well as potential costs of installation and maintenance; is provided for the practitioner to determine which treatment(s) best suit the site under consideration. Guidance is also provided for the methodology of conducting a speed study to determine the speed characteristics of a site; as well as links to resources for additional information. The project identifies a number of research needs specific to particular treatments as well as the general need for field research of the recommended countermeasures specifically on approaches to high-speed rural roundabouts.
