Determining the Effectiveness of HOV Lanes

This document is the final report for the two-year PATH Project “Determining the Effectiveness of HOV Lanes”. It has been supported by the California Department of Transportation (Caltrans). The primary objectives of this project have been to evaluate freeways having on-freeway HOV lanes in terms of vehicle-travel, person-travel, occupancy distribution, shape and duration of the peak period, congestion patterns, and air quality both in the HOV lane and the adjacent mixed-flow lanes. Based on a comprehensive literature review an extensive list of reference was developed, along with summaries synthesizing the state of the knowledge regarding the effectiveness of HOV lanes and their impact on air quality. Historical and current field data were assembled and analyzed for all of California’s HOV lanes. The analysis revealed that there is strong public support for HOV lanes, California’s HOV lanes are well utilized and offer significant time savings to ride sharers, that there is a steady growth in the number of carpoolers, violation rates are low, and that over time, HOV lanes cause carpools to last longer. The air quality module in the freeway simulation model FREQ was updated to reflect the most up-to-date techniques for predicting air quality developed by the California Air Resources Boardin their EMFAC model. The new air quality methodology was also used to develop an off-line air quality module for use with PeMS data. The design of a successful HOV lane facility is a very difficult task and requires careful analyses prior to implementation in order to move toward an optimum design. Accurate data on vehicle occupancy distributions and traffic demand levels are essential for realistic modeling of such facilities. To demonstrate the types of analyses that would be useful in this process, the modified freeway simulation model FREQ was applied to two freeway study sites, one in Northern California and one in Southern California. The FREQ model proved to be well suited for investigating various combinations of HOV lane design and operating parameters. As traffic demands increase and HOV lanes generate changes in ridesharing choices, the continued success of HOV lane operation is likely to require changes in HOV lane design and operations. This will require careful monitoring of the HOV lane facility and further modeling analyses.