Safety of High-occupancy Vehicle Lanes without Physical Separation

This study addresses safety issues associated with the operation of freeway high-occupancy vehicle (HOV) lanes that are not'separated by physical barriers from adjacent, general-purpose traffic lanes. Accident frequencies and characteristics obtained from 14 months of operation of an HOV lane in the greater Los Angeles area, together with similar data for 6 years' prior to the opening of the lane, are analyzed to evaluate the safety impacts of the lane operation. The analyses rely on comparisons of accident characteristics associated with the HOV lane to those associated with both temporal and spatial control groups. Changes in accident characteristics are also related to existing patterns of freeway congestion. The results of the case study indicate no adverse effect on safety conditions that could logically be attributed to the HOV operation; all of the changes in the patterns of reported accidents can be explained by changes in the location and timing of traffic congestion. Although no overall change in the exposure to accidents was found, there is a significant migration of accident locations due to the combination of relief of congestion in the project area and a corresponding creation of more severe traffic bottlenecks downstream of the project.