Traffic operation and safety performance of the new roundabout and median U-turn combination design in comparison to four roundabout designs

This study evaluates the proposed roundabout and median U-turn (R/MUT) combination design as a potential solution to improve traffic operations and safety at congested roundabouts. Using microsimulation, three variations of the R/MUT design were compared with four traditional and modern roundabout designs, including the turbo roundabout, across three traffic volumes: 1 800, 2 500, and 3 000 vehicles per hour. The R/MUT design, which redirects three traffic movements to a U-turn crossover approximately 600 ft (182.88 m) from the roundabout center, aims to shift some conflicts from the roundabout to the crossover, enhancing capacity and safety. This design addresses the common issue of asymmetric demand distribution at intersections, improving performance and reducing overall travel time in high-traffic scenarios, similar to the peanut-shaped roundabouts recently built in the USA. Results show improvements in travel time, with the R/MUT semi 2+1 reducing travel time by up to 40% at a volume of 2 500 vehicles per hour, and the R/MUT 2+2 cutting travel time by up to 23% at a volume of 3 000 vehicles per hour, compared to traditional roundabout designs. At lower traffic volumes, R/MUT designs showed limited or no benefits. Surrogate safety assessment model (SSAM) analysis revealed conflict reductions of 6% to 32%, with fewer conflicts at the roundabout circle and a decrease in eastbound sideswipe crashes. However, higher lane-change conflicts were observed due to weaving near the U-turn crossover. Overall, the R/MUT design proved highly effective in high-traffic scenarios and is a promising solution for critical locations such as stadium exits or bridge approaches, where traffic demand is higher on one or two intersection legs. The findings underscore the R/MUT design’s potential to enhance roundabout performance and safety in near-capacity conditions.