This work is part of a three year program to foster the development, evaluation, and deployment of forward crash avoidance systems. The work performed during the first and second year of this program has addressed adaptive cruise control and warning based upon the motion and proximity of preceding vehicles in the path of travel. The work fr this second year has emphasized features of ACC systems that could make them either more convenient and comfortable through the use of adjustable headway or safer through the use of warnings. The second year of the project presents detailed information on: driver-adjustable headway time, observations concerning drivers, neural network methods for finding driving episodes, an audio prompt for ACC intervention (crash warning), implementation of a brake-assisted lo-decel-cue, and use of an ACC test vehicle with 0.18 g deceleration authority. The findings of the first year and the work this year indicate that ACC systems with limited deceleration authority (0.05 g) can provide a level of headway control that is both useful and desired by many drivers. When controlling headway manually, drivers tend to follow preceding vehicles at closer range and to close-in more rapidly than they do when using an ACC system under similar road conditions. There are differences between the choices of headway time made by drivers from various age groups. This year's work has included the development of an audio warning based upon using range and range-rate data to compute the deceleration needed to meet a selected headway goal. Another type of warning, as well as an extension of the control authority of the ACC, was by provided by downshifting the transmission when a deceleration greater than that of coastdown was required. An additional warning system called a "lo-decel-cue" was also studies this year. This system used the foundation brakes, though only in a constrained manner, to warn the driver.
Abstract