A Methodology for Assessing the Benefits of Coordination on the Safety of Vehicles

Abstract

In this article, we present a methodology for assessing the benefits of different vehicle coordination strategies on the safety of a platoon during emergency braking. One can say that a coordinated braking strategy B is more beneficial than a strategy A, if strategy B leads to a larger reduction in the probability of a collision, the expected number of collisions, and the expected relative velocity at impact as compared to strategy A. We consider an emergency braking scenario, in which the lead vehicle brakes at its maximum capability and the following vehicles coordinate their braking. The sequence of maximum braking capability (i.e., deceleration) of vehicles in the platoon is assumed to be a sequence of independent and identically distributed random variables; this distribution is assumed to be discrete and known. Due to coordination among vehicles, however, the “effective” deceleration of a following vehicle may not necessarily be its maximum value. The problem of assessing the benefits of coordination can be formulated as three subproblems. The first subproblem deals with determining the probability distribution of the “effective” deceleration of following vehicles during emergency braking. It is intuitive that the smaller the variance of this distribution, the greater the safety benefits are. We define three metrics of safety through the concept of a violation. A violation occurs in a platoon if the “effective” deceleration of a following vehicle is smaller than that of its predecessor. The second subproblem deals with determining the probability of occurrence of a violation, expected number of violations, and the expected relative velocity corresponding to a possible collision as a function of the difference in the braking capabilities of successive vehicles in a platoon. The probability of an intervehicular collision and the expected number of collisions are related to the probability of a violation and the expected number of violations, respectively. The concept of a violation circumvents the need for a detailed consideration of the mechanics of a collision. A method is provided here to compute these metrics of safety using a Markov chain. The third subproblem deals with conducting Monte Carlo simulation to corroborate the safety benefits of coordination during emergency braking and the viability of our analytical approach to provide the correct trend.

Keywords:

• Transportation Safety
• Collision Avoidance
• Safety Metrics

Acknowledgments

This work was supported by the CaliforniaPATH program under MOU 319.