Enhance Traffic Safety at High-Speed Intersections through Vehicle Tracking

Abstract

Traffic safety at high-speed intersections remains the dominant problem in traffic operations. Although advance detectors are used to detect arriving vehicles ahead of time, most detectors used in the field (inductive loops, microwave, etc.) provide only “point” detections for which control algorithms are developed according to the design speed. Because of variations in approaching speed, vehicle size, roadway and weather conditions, those control algorithms can only be effective for a certain portion of the arriving traffic that “fits” the assumed conditions. This research looks into the vehicle tracking capability of the IntelliDrive technology to obtain the instant vehicle position and speed data for the signal control system. In addition, the technology can incorporate and provide to the system other information such as vehicle type (size), roadway surface, and weather conditions. By using such input in real time, the signal system determines the green time extensions most needed to protect vehicles on the main road (and the minor approaches as well). Besides enhancing safety, this design also improves operational efficiency because unneeded green extensions can be avoided. The effectiveness of the proposed signal operation concept is evaluated and demonstrated in this paper through a test of its ability to reduce the probability of max-out in comparison with other existing methods. BACKGROUND Signalized intersections with approach speeds greater than 72 km/hr (45 mph) present a major safety concern because of the traffic from the cross roads. At these intersections, drivers on the main road must decide what to do at the onset of the yellow light, where a decision to stop may result in a rear-end collision while continuing through the intersection may produce a right-angle accident. To minimize the potential hazards, current signal designs make use of advance detectors and traffic actuated controllers. Actuated control dynamically responds to varying traffic demands and improves the safety of the intersection by extending the green to allow the driver to clear the dilemma zone if the driver cannot safely stop the vehicle before the signal indication changes. Despite the use of green extensions, a problem still exists due to different approaching speeds selected by drivers with different experiences and attentiveness levels and affected by varying driving conditions. For example, if the approaching speed is greater than the design speed or if the roadway friction drops because of a wet pavement surface, the dilemma zone tends to increase in length and move further