Impacts of freeway high-occupancy vehicle lane configuration on vehicle emissions

In California, high-occupancy vehicle (HOV) lanes on freeways have been implemented with two different configurations – continuous access HOV lanes, primarily used in Northern California, and limited access HOV lanes, primarily used in Southern California. Using a new emissions modeling methodology that integrates a microscopic traffic simulation model (PARAMICS) with a modal emissions model (CMEM), this study estimates and compares vehicle emissions contributed from these two types of HOV lane configurations. Under various scenarios with different levels of vehicle demand and percentage of HOVs in the traffic mix, it is found that the freeway with continuous access HOV lane consistently produce lower levels of pollutant emissions compared to the freeway with limited access HOV lane. This is primarily due to the highly concentrated weaving maneuvers that take place on the dedicated ingress/egress sections on the freeway with limited access HOV lane, which cause relatively higher frequency and magnitude of acceleration/deceleration events, resulting in higher emissions on these sections of the freeway.