Left-Turn Geometrical Attributes: A Microsimulation Approach to Signal Optimization

Abstract

The ordinary signalized intersection geometry and control are facing tremendous traffic challenges. Signal timing control and innovative geometric designs contribute to mitigate congestion at signalized intersections worldwide. The author has investigated a geometric design case in Qassim region, in Saudi Arabia which involves a roundabout intersection. The intersection was recently reconstructed with a new geometric design involving partial Exclusive Left- Turn Bays. The research was aimed to investigate three different geometric designs of a partial exclusive left turns signalized intersection, a roundabout intersection, and a proposed full exclusive left turns signalized intersection. Analyses for the existing case, the roundabout, and the exclusive left turns were coded and validated using microsimulation model (VISSIM) with field collected data from the studied signalized intersection. The results showed that, despite fewer improvements in vehicle delays and queue length (meters) of the proposed full exclusive left turns in the comparison with the existing partial exclusive left turns, the geometry designed with a roundabout case yield shorter queue lengths and vehicle delays than the case of signalized intersections designed with partial or full exclusive left turn bays in certain traffic volume levels.