In order to clarify the effect of different time headways and lead car's decelerations on visual distraction and its impact on collision risk during car-following a driving simulator study was conducted. Moreover the experimental investigation considered system effectiveness of a forward collision warning system as for decreased collision risk. Results showed that compared to short time headway, long time headway induced long duration time of visual distraction during car-following. This effect

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... was significant when a lead car decreased its speed mildly. Collision risk due to lead car's deceleration was low for long time headway during car-following compared to short time headway even thought visual distraction was induced. However there was a possibility that long time headway led to long duration time of visual distraction resulting in increased collision risk. In case of the alarm trigger logic used in this study, alarms effectiveness for decreasing collision risk was proven because early alarms were given for short time headway. It can be said that longer headway time does not always guarantee decreased collision risk.