Simulation-based analysis of variable speed limit for traffic performance and safety during incidents

This study employs a Vissim–Matlab component object model (COM)-based microsimulation model to evaluate the effectiveness of variable speed limit (VSL) strategies during traffic incidents. This study examines two VSL strategies on a 2.7 km section of Thailand’s Motorway No. 7: VSL1 with 1 km spacing and VSL2 with 2 km spacing. Simulation results show that under peak volume conditions, the VSL1 strategy outperforms both the existing scenario and VSL2 in terms of traffic performance and safety. This advantage holds for single-lane closures for both short and long periods. However, for two-lane closures with prolonged incident-clearance times, the VSL system should be temporarily deactivated to prevent increased congestion. Sensitivity analysis results indicate that under mild to moderate traffic volumes, VSL1 and VSL2 perform similarly in both traffic performance and safety across single- and double-lane closures and both closure durations. Both strategies outperform the existing scenario in nearly all cases. The VSL implementation yielded up to an 18% increase in average speed and an 88% reduction in rear-end conflicts. The magnitude of these improvements increased as traffic demand decreased. However, under congested conditions with two-lane closures, the VSL system should remain inactive regardless of the expected incident-clearance time.