Collision warning systems (CWSs) are in development in the intelligent transportation system domain to reduce collision accidents. The lead time of warning messages is a crucial factor in determining system effectiveness in the prevention of accidents. The present experiment studied the effects of controlled lead time at 16 levels (predetermined time headway from the subject vehicle to the collision location when the warning message was issued) and lead vehicle conditions (without vs. with lead vehicle) on driving behaviors in various collision scenarios. The results indicated the controlled lead time and lead vehicle conditions significantly affected driver performance. Maximum effectiveness of warning messages was achieved when the controlled lead time was within the range of 4.5s to 6s. When the warning messages were relatively late, the existence of a lead vehicle brought greater safety benefits and more abrupt deceleration. Potential applications of the results in designing of CWSs are further discussed.