Safety and Efficiency Tradeoff Analysis for Automated Highway System: Part 3: Longitudinal Separation on AHS: A Trade-off Between Collision Probability/Severity and Capacity

This report develops a probabilistic model for analyzing longitudinal collision/safety between an abruptly decelerating vehicle and its immediate follower on an Automated Highway System. The input parameters are the distance between the two vehicles, their common speed prior to the failure, the reaction delay of the following vehicle and a bivariate distribution for the two deceleration rates. The output includes the probability of a collision and the probability distribution of the relative speed at collision time. These safety consequences can be used to balance the desire to increase AHS capacity with the safety requirements. We use this model to compare the safety consequences associated with the platooning and "freeagent" longitudinal-separation rules. We also demonstrate that the free-agent rule implemented with a potential technology of fast and accurate emergency deceleration, under some reasonable conditions, can avoid collisions while offering a high freeway capacity previously thought possible only under the platooning rule. This model has many other applications.