Simulation-based Analysis of Variable Speed Limit for Traffic Performance and Safety During Incidents

Traffic congestion poses substantial issues to the environment, society, and the economy, with traffic incidents playing a crucial role. Intelligent Transportation Systems, particularly active traffic management tactics such as Variable Speed Limit (VSL) systems, offer options for reducing congestion and increasing safety. VSL systems typically include fixed sensors to assess traffic conditions and dynamic variable message signs (VMS) positioned at predefined places to implement adjusted speed limits based on the average, volume, and percentage occupancy. A simulation model was developed using the VISSIM COM interface with MATLAB to evaluate the effect of VSL strategies on traffic safety and performance during incidents. This study compared the effectiveness of VSL with VMS spacings at 1 km and 2 km intervals. The study area encompasses Motorway Number 7, which spans from KM 19+000 to KM 21+500. The results show that VSL systems significantly improve traffic flow, particularly in mild to moderate congestion situations. However, during periods of high traffic congestion, the effectiveness of VSL system decreases because speed limit signs may not reduce vehicle speeds effectively before reaching incident areas. To optimize safety and performance benefits, it is recommended to install VMS signs at intervals of 1 kilometer. The analysis of VSL with VMS spacing at 1 kilometer at different flow rates (0.25, 0.50, 1.00, and 1.25 times as much as the peak traffic volume) reveals up to 48%, 18%, 15%, 89%, 88%, 79% and 84% improvement in average delay per vehicle, average speed, total travel time, average number of stops per vehicle, rear-end conflicts, lane change conflicts, and total number of conflicts, respectively.