Summary

High-Occupancy-Vehicle (HOV) lanes have been implemented in many highway segments in the urban areas. The HOV facilities are aimed at elevating the highway utilization effectiveness and ultimately improving the overall mobility for the state transportation systems. To facilitate smooth and safe operations of traffic flows typically at relatively higher speeds within the HOV lanes, certain highway segments have utilized buffer zones to separate the HOV traffic streams from the non-HOV traffic in adjacent lanes. To allow traffic to enter and exit the HOV lanes, these buffer-separated lanes are provided with limited-access ingress and egress zones at selective segments. As can be expected, if numerous lane-change or merging and diverging maneuvers are made under heavy-traffic conditions and considerable speed differential between the interacting vehicles, then hazardous situations may occur frequently. There are strong incentives to (a) understand the implications of HOV facilities such as the limited-access buffer zones on traffic flows and safety factors, and (b) establish supporting criteria and guidelines in selecting configurations to allow effective utilization of HOV facilities as well as to minimize the occurrence of vehicle collisions. This research is built on the premise that a systematic approach in evaluating the collision statistics and analyzing field traffic data can significantly satisfy the critical needs and accomplish the ultimate objectives of Caltrans on this subject. The research team will leverage their efforts and carry out an investigation of highway and traffic attributes that can be potentially linked to the causative factors recorded in accident statistics. In addition, we also propose the use of field observation to supplement the safety factor analysis by capturing traffic flow information with radar and video to fully understand the traffic interaction at selected observation sites.