Simulation Analysis of Truck-Restricted and High-Occupancy Vehicle Lanes

Numerous studies have reported the efficacy of high-occupancy vehicle (HOV) lane restriction and truck lane restriction implemented independently, but the simultaneous use of both restrictions on an urban freeway corridor raises numerous operational and safety issues. This research study analyzed the operational and safety experience of an 83-mi corridor of I-95 in South Florida that has both HOV and truck lane restriction. Results of a field-validated VisSim simulation model showed that high-occupancy vehicles and automobiles gained significantly more travel time savings and speeds on the restricted lanes than on the general lanes. Also, vehicle queue lengths around critical merging and diverging areas increased significantly as the percentage of trucks increased. Results indicated that during peak traffic conditions right lanes had higher lane occupancy than left lanes, whereas during off-peak traffic conditions center lanes carried more vehicles per lane than the outermost lanes; these results suggest that congestion on right lanes forces automobiles to use left lanes. Furthermore, results showed that most lane changes occurred during peak traffic flow conditions—about twice that of off peak—and appreciable speed differences existed between restricted and nonrestricted lanes. Simulation results for off-peak traffic conditions did not show any noticeable changes in traffic operating characteristics resulting from lane restriction strategies. On the basis of these results, it can be fairly concluded that on urban freeways significant operational and safety benefits of the combined implementation of HOV and truck lane restrictions accrue during congested traffic conditions rather than during uncongested conditions.