Impact of Restricted Crossing U-Turns on Vehicular Emissions

Abstract

In recent years, several innovative intersections have been designed and implemented as an alternative to typical two-way intersections. The Restricted Crossing U-Turn (RCUT) is a type of innovative intersection design that limits left-turns from the minor road by directing cross-street traffic to one of two auxiliary U-turns. This design seeks to improve intersection safety by reducing conflict points, as well as increase the capacity and decrease travel time on certain movements, such as the mainline through traffic. However, the change in the cross-street vehicle paths through the intersection can affect acceleration profiles and emissions. This research develops a methodology to test emission differences through simulation. Models of an RCUT and a traditional intersection were constructed and tested under varying turn volumes and mainline speeds conditions. CO2 and NOx emissions were calculated using Vissim simulation vehicle trajectories and the Motor Vehicle Emissions Simulator (MOVES) model. The modeled emissions values were used to compare the overall emissions performance of the RCUT versus a traditional intersection layout. The RCUT intersection layout was associated with an increase in average cross-street through and left-turn movement emissions because of the longer travel distances. However, a reduction in emissions was seen on the main line, primarily as a result of the additional green-time afforded by the RCUT design. Where the mainline volume to side-street ratio becomes sufficiently large, the RCUT performed better in overall intersection emissions levels.