A systematic review on close-following or short headways: preliminary findings

Rear-end crashes account for the highest number of crashes among all crash types. An important component in understanding rear-end crashes is close-following tendency of drivers. However, headway is not consistently defined or measured in the research literature. In order to consolidate common headway definitions, a systematic review was conducted to summarize the definitions of headways and methods of measurement. Over half of the reviewed articles did not clearly define headway, which includes contextualizing reference points of headway measure (e.g., bumper/axle/rear) and explaining the accuracy of setups used to measure headway.