UC Irvine Institute of Transportation Studies

The objective of this study was to evaluate the traffic safety of freeway High Occupancy Vehicle (HOV) lanes that are not separated by physical barriers from adjacent, general-purpose traffic lanes. The purpose of the HOV lanes is to offer an incentive to motorists to form carpools, thereby providing some relief to congestion attributable to the relatively high number of single-occupancy vehicles utilizing urban freeways. The research was aimed at determining the causes of any changes in safety conditions due to the operation of such lanes, and identifying possible actions to mitigate any adverse safety impacts.

The study focused on two HOV lane operations in the greater Los Angeles area: One is located on State Route 91 (SR-91, the Riverside Freeway) in Los Angeles County; the other is on State Route 55 (SR-55, the Costa Mesa/Newport Freeway) in Orange County. Both of these facilities have been implemented through partial removal of the left median shoulder and restriping of the lanes.