FDOT Sponsored Research, BDK77 977‐21 (Cost-share project for STRIDE Center)
Authors: Ruth L. Steiner, Scott Washburn, Lily Elefteriadou, Albert Gan, Priyanka Alluri, Dimitra Michalaka, Ruoying Xu, Shanty Rachmat, Benjamin Lytle, Amy Cavaretta
Report Completed:  March 2014

ABSTRACT:

Transportation engineers and planners are becoming more interested in using roundabouts to address access management and safety concerns in the transportation system. While roundabouts are being used increasingly in a variety of contexts, existing research does not provide detailed guidance on how to evaluate the use of roundabouts as a form of access management. This Florida Department of Transportation (FDOT) research project has three primary components: a review and assessment of national and state guidance related to roundabouts and access management, a safety analysis of all 283 roundabouts in Florida, and an operational analysis of selected roundabouts. Literature related to safety, access management, and multimodal transportation (especially for bicyclists and pedestrians, and roadway capacity associated with the use of roundabouts) is reviewed, and gaps in knowledge regarding the use of roundabouts are identified, particularly as they apply to safety, access, and capacity. One of the findings of the literature review is that little research has been completed on access management near roundabouts. A review of national and state guidance identifies major studies including NCHRP 672 and guidance in Kansas, Wisconsin and Virginia that recommend intersection and driveway spacing similar to that recommended for un‐signalized intersections. The safety and operational analysis identifies four areas of concern: corner clearance, including stopping site distance (SSD) and intersection sight distance (ISD); the need for guidance on the functional area near roundabouts including driveway and intersection spacing, and the use of medians; access to major activity centers; and safety of vulnerable road users, especially bicyclists and pedestrians. The operational analysis confirms previous research that shows that roundabouts are similar to un‐signalized intersections, but the differences may influence the operations and safety within the functional area of the roundabout. An assessment of the primary FDOT utilized software tools focuses on the current suitability of these software tools to assist practitioners in assessing the suitability of incorporating roundabouts into existing and proposed roadway configurations. Recommendations are made for additional national research on guidance on driveway and intersection spacing, medians, and SSD and ISD in the different contexts in which roundabouts are installed. Changes to the FDOT’s Access Management Tools, Median Handbook and Driveway Information Guide are also recommended along with the development of Florida‐specific parameters for capacity and safety analysis. Modifications to roundabout design guidelines and handbooks for access management will lead to safer, more effective, and ultimately, better performing roundabouts for all users of Florida’s transportation system and throughout the United States.

 (Source: FDOT report, March 2014)