Development of a Surrogate Conflict Indicator for Freeway Exits Using Trajectory Data
Crash occurrences are random rare events which are difficult to detect and reconstruct. Evaluating traffic safety using crash surrogate measures instead of historical crash data is attracting more and more attention. The trajectory, a continuous function
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Abstract Crash occurrences are random rare events which are difficult to detect and reconstruct. Evaluating traffic safety using crash surrogate measures instead of historical crash data is attracting more and more attention. The trajectory, a continuous function of a vehicle’s temporal-spatial kinestate, is capable of depicting the process of crash potentials by means of theoretical analysis or simulation. The trajectory provides easy access to accurate calculation of the commonly used safety surrogate indicators like TTC and PET, which are difficult to obtain in practice. TTC and PET are the time differences between two vehicles during a quasi accident process. Compared with the situation in the final conflicting point, two vehicles may encounter a smaller distance or a bigger speed variation while approaching the conflict point. TTC and PET are deficient in describing abreast driving, or distinguishing the severity levels for approximately equal TTC (PET) cases. To remedy these shortcomings, this paper proposes a surrogate indicator Kj, the ratio of conflicting distance divided by relative speed. And an exponential model is developed to predict the conflict probability. Kj and the conflict probability are both time frame based, illustrating the changing process at each time frame during a conflict phase. The indicator Kj and conflict probability make it easier to describe the conflict mechanism and distinguish the levels of conflict severity. Keywords Conflict
Surrogate safety indicator Trajectory Freeway exit
1 Introduction The freeway exit is the most important connection between a freeway mainline and a crossroad. Most geometric designs change right before the deceleration lane or the ramp taper begins. Because the curved exit ramp are unexpected, drivers may need T. Guo (&) X. Jiang W. Fan School of Automation, Nanjing University of Science and Technology, #200 Xiao Ling Wei, Nanjing 210094, China e-mail: [email protected] © Springer Science+Business Media Singapore 2017 H. Lu (ed.), Proceedings of the Second International Conference on Intelligent Transportation, Smart Innovation, Systems and Technologies 53, DOI 10.1007/978-981-10-2398-9_6
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to make a lane change, weave, or diverge to the desired lane, or even brake sharply to avoid a collision. Drivers have an elevated crash risk when they drive on freeway entrances and exits as compared with other sections of freeways. According to crash data from the U.S. Fatality Analysis Reporting System and General Estimates System in 2001, 18 % of all Interstate crashes occurred at interchanges, although such locations constituted less than an estimated 5 % of total freeway mileage. Of these interchange-related crashes, 83 % occurred on entrance or exit ramps [1]. Accidents are rare random events which are difficult to capture or reconstruct. Furthermore, more than 90 % accidents are caused by sophisticated human errors. Therefore, the accident statistics alone are of little use to support the research purpose to reduce accident freq
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