From 60 689 km of naturalistic driving data, 1 613 car following events were identified. Two major parameters of car following behavior were analyzed—time headway and reaction time. The results show that forward collision warning(FCW) did not have a significant effect on time headway; while FCW resulted in a 0.13 s decrease of reaction time in daytime driving, and a 0.09 s decrease when a following vehicle had higher speed than the lead vehicle.