UC Irvine

Carpool lanes, technically called High Occupancy Vehicle (HOV) facilities have operated in the state of California for decades; however, the vehicle speeds on HOV facilities have significantly decreased in many locations and now meet the Federal Standard of HOV degradation. Such degradation is found on both types of HOV facilities used in California – with continuous access and with limited access. This study is interested in the pre-and-post comparison of the performance of an HOV facility (the SR55 freeway in Orange County) with significant degradation, on which the access type was converted from limited to continuous. The comparison uses a Tobit regression analysis, an incentive/disincentive analysis, and a time savings analysis. The study considers the performance in multiple years before and after the conversion, as well. The modeling dataset contained data from the California PeMS (Performance Measurement System) and new data on geometry variables which were manually collected on the two access-control configurations. The Tobit regression model explores the influencing factors involved in the degradation problem. As the results show, the geometric design of the freeway affects the degradation of HOV lanes. In terms of the speed differences, the degraded carpool lanes are still able to offer incentives to the user. On the basis of the time savings analysis, the degraded HOV lanes are found to have had worsening travel time delays over the years since the conversion, although the general purpose lanes’ travel times improves sufficiently to yield an overall benefit from the conversion.