Recently, various systems that use ITS for improving safety and comfort in driving have been developed. This study verified effects of the warning system that informs the sudden deceleration of the two preceding cars. We used a fixed driving simulator in the experiment. Information about the state of the two preceding cars provided by the inter-vehicle communication that is assumed to be already widespread. As a result, compared to a warning about the sudden deceleration of the lead car, the collision-avoidance warning according to the two preceding cars shortened braking response times especially during looking-aside driving. It was indicated that the rapid braking warning of the two preceding cars improved the safety performance of collision-avoidance system.
