Examination of Differentiated Per-Lane Speed Limits on Improving Traffic Safety: Microscopic Traffic Simulation Approach

Speed control has a direct impact on safety and mobility of road users. The objective of this study is to examine the effectiveness of Differentiated Per-Lane Speed Limit (DPLSL) in improving safety by estimating predicted traffic conflicts and collisions before and after the implementation of DPLSL. The study area is 9 Km with 7 in and off ramps in two directions along Salwa expressway in Doha in Qatar, which has a history of speed-related collisions. Surrogate Safety Assessment Model (SSAM) along with Vissim microsimulation software was utilized to measure the predicted conflicts for both Uniform Speed limit and DPLSL scenarios. Trajectory files produced by Vissim were used by SSAM to predict the conflicts. Total yearly collisions were correlated with total conflicts for each simulation, the expected collisions per hour in a year. Next, the total number of collisions in a year under Uniform Speed and DPLSL have been estimated. The findings show that the DPLSL scenario produces expected collisions less than the Uniform Speed in seven out of the nine simulations, and the total average of the expected collisions under DPLSL is less than the average of expected collisions under uniform Speed by 5 percent. It can be concluded that DPLSL is an effective technique for improving safety.