Assessment of Different Intersection Designs to Accommodate Left Turns Through Indirect Maneuvers

Abstract

Although there are studies that compared between indirect left-turn treatments such Median U-turn (MUT) or RCUT to the Conventional Intersection (CI) designs, very few have compared between the operational performances of MUT versus RCUT. Furthermore, few studies on the Quadrant Roadway Intersection (QRI) were found in the literature. The main objective of this paper is to assess different designs for the accommodation of left turns through indirect maneuvers. Traffic performance of the proposed intersection designs was evaluated based on microsimulation. The results revealed that the difference between the two designs, RCUT and MUT lies in the amount of traffic rerouted to the crossover intersections. Increasing the traffic downstream of the main intersection to the crossover intersection still has an effect on the main intersection’s operations. Proper design and spacing is needed at the crossover intersection to mitigate this effect. The analysis also showed that at higher volume levels, RCUT throughput becomes restricted compared to the MUT which was attributed to the left turn effect at the main intersection. However, the RCUT showed 52% improvement over the MUT in average speeds. RCUT also showed 66% over MUT in delay savings and one-year cost reductions when compared to the conventional intersection at 200% volume level. The assessment of the Quadrant Roadway Intersection (QRI) design revealed 12% increase in throughput compared to the CI when CI reaches capacity with 48% increase in speeds and 66% reduction in delay. The cost of the connector roadway is the greatest cost and affects the total project cost depending on the available right of way. Some of the costs associated with the QRIs could be slightly compensated by the reduced widths at the main street intersection. Overall, QRI is significantly cheaper than the grade separation alternative.