The Relationship between Different Safety Indicators in Car-following Situations

Studying different aspects of car-following behavior is still of strong interests for many researchers, due to its usefulness in many applications, such as for further development of traffic simulators and active safety systems (e.g., Adaptive Cruise Control and Autonomous Emergency Braking). This paper investigates the relationships between several safety indicators (e.g., time gap, gap distance, time to collision) in car-following situations, and analyzes which of these indicators affect driver's behavior in car-following situations and how. All analyses are done using real driving data collected in China. The paper also suggests parameters that can be used for defining, identifying, and extracting car-following events from real driving data. Results indicate that time gap is less sensitive to the variations in speed and road condition compared with gap distance in this test. TTC in the low speed range of subject-vehicle is found to be steady compared with other speed ranges, so is the time gap in the high speed range. Therefore, time gap is more suitable to be the safety indicator compared with gap distance in the future car-following research. Time gap is found to be more appropriate for the analysis of car following behavior in the high speed ranges, but both TTC and time gap should be used as part of the safety indicator for the low speed ranges.