Performance evaluation of roundabouts for traffic delay and crash reductions in Oxford, MS.

789357827Final report; June 30, 2011.PDFTech ReportFHWA/MS-DOT-RD-11-213MS-DOT-RD-11-213Highway capacityRoundaboutsTraffic delayAccident dataAccident ratesTraffic congestionTraffic engineeringTraffic flowTraffic safetyTraffic surveysMississippiMississippi. Dept. of TransportationUddin, WaheedUniversity of Mississippi. Dept. of Civil EngineeringMississippi. Dept. of Transportation. Research DivisionNTL-OPERATIONS AND TRAFFIC CONTROLS-OPERATIONS AND TRAFFIC CONTROLSNTL-OPERATIONS AND TRAFFIC CONTROLS-Traffic FlowNTL-PLANNING AND POLICY-PLANNING AND POLICYNTL-REFERENCES AND DIRECTORIES-StatisticsUS Transportation CollectionDue to increased traffic volume, congestion, and capacity limitations, two roundabouts have been constructed on South LamarBoulevard ramp intersections with MS Highway 6 in Oxford, MS. Roundabouts replaced the existing signalized intersectionon the north and stop controlled intersections on the south side of the South Lamar Boulevard and MS Highway 6 Interchange.The overall objective of this study was to assess the performance of the roundabouts in Oxford with respect to traffic flow,capacity, and safety improvements, and to determine the public perception of roundabouts by means of an opinion survey.Detailed post-roundabout traffic movement volume and crash data were collected and compared with the pre-roundabout datato assess the in-service performance of the roundabouts. Traffic flow microsimulation and capacity analysis methods wereused to evaluate performance of the roundabouts. The results of the Oxford roundabout study showed significant improvementin traffic flow, crash reduction, and reduction in vehicle emissions. It was found that the conversion of the intersections toroundabouts improved traffic flow by reducing average delay by 24%, idling time by 77%, and fuel wastage by 56%. Overallvehicle emissions from idling were reduced significantly including 56% in CO2, 80% in VOC, and 77% in CO, NOx, and PM10.This conversion of stop-controlled intersections to roundabouts increased the average speed by 67% and improved level ofservice of both roundabouts. The roundabout conversion increased the mean speed on the South Lamar interchange by 67%and improved level of service for both intersections. The roundabout junctions improved safety performance through a 37.5%reduction in crashes and a 60% reduction in the number of crashes resulting in injury. The reduction in overall crashes in thestudy area reduced comprehensive cost by 54.4%. Total user cost saving from reductions in travel time, fuel wastage, andcrash cost combined is $806,018 annually. These benefits paid off the total cost of construction of the two roundabouts withintwo years. The resulting B/C ratio is 6.2 over a period from 2009 to 2016. Additionally, significant societal benefits areexpected from reductions in vehicle emissions. Also, an anonymous public opinion survey overwhelmingly demonstratedfavorable results and provides support to consider more roundabout junctions in place of stop-controlled intersections. Thestudy results indicate that roundabouts are performing well as intended. Some constructive comments suggested by the public,such as flashing lights on signs, can be implemented by the Mississippi DOT to enhance traffic flow and safety