Introducing Two New Versions of Continuous Flow and Median U-Turn Combination Intersection Designs

Abstract

In recent years, departments of transportation (DOTs) have shown an interest in implementing alternative intersections that combine features of two (or more) different designs. However, the current literature on the performance of these combination designs is limited. This paper reports on an assessment of the traffic operations and safety of two new combination intersection designs—continuous flow and median U-turn combination (CFI/MUT combo) and redirect two left-turn and one through (redirect 2L&T)—in comparison to four existing intersection designs: conventional, partial MUT, partial CFI, and reduced conflict intersection (RCI). Over 1,000 microsimulation runs were conducted in this study, considering different traffic demands, turning traffic ratios, and traffic demand distributions. For all simulation scenarios, traffic signals were optimized using Synchro, and the optimized signal data were imported into PTV VISSIM to obtain several performance measures such as vehicle travel time, queue length, and the number of stops for all designs considered. Safety analysis was also conducted using surrogate safety measures, including the US Federal Highway Administration’s Surrogate Safety Assessment Model (SSAM). Based on the results, both the CFI/MUT combo and redirect 2L&T showed potential in improving safety and operations at conventional intersections. The CFI/MUT combo exhibited statistically similar vehicle travel times to a partial CFI and outperformed all other designs. The redirect 2L&T demonstrated statistically similar travel times to the partial MUT but resulted in longer queue lengths. From a safety standpoint, the RCI is the safest intersection design among those considered.