Summary

Highway ramps, entry or exit, are junction points where a high level of traffic interaction occurs. Ramp connections are generally designed and constructed to minimize potential conflicts, although geometric constraints and traffic capacity issues have to be taken into consideration along with safety concerns. Due to the weaving and mixing of traffic flows, unavoidably hazardous conditions will arise. As can be expected, if numerous lane-changing or merging and diverging maneuvers are made under heavy-traffic conditions and considerable speed differential between the interacting vehicles, then dangerous situations may occur frequently. The accident statistics in California from the past reflect this concern and reveal a relatively high number of incidents at highway ramps. As a matter of fact, a ramp category exists in the process and methodology for the search of high-concentration collision locations. One long-term goal, also a near-term focus, sought by Caltrans is to improve highway safety and to reduce numbers of crashes, fatalities, and injuries. Therefore, there are strong incentives to (a) understand the implications of ramp connectors on traffic flows and safety factors, and (b) establish supporting criteria and guidelines in selecting ramp configurations to minimize the occurrence of vehicle collisions while achieving the necessary capacity and meeting other design criteria. This research is built on the premise that a systematic approach to evaluating the collision statistics and analyzing field traffic data can meaningfully satisfy the critical needs and supplement the ultimate objectives of Caltrans with a safety strategy. The research team will leverage its experience in working with highway database and accident database and carry out an investigation of highway and traffic attributes that can be linked to the representation of causative factors in ramp 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. The interaction between vehicles in lane changing, merging and diverging maneuvers will be analyzed.