Close Following Behavior: Estimation of Desired Gap Headway Using Loop Detector Data (TECHNICAL NOTE)

The desired gap headway of drivers, while close following, represents the main parameter in determining the following distance between vehicles.  This paper uses the raw individual vehicles data taken from loop detectors for millions of vehicles used M25 and M42 in order to estimate the gap headway distributions between successive pairs of vehicles.  The data used in this paper were filtered so as to focus on the cases of close following behavior only and more than quarter million pairs of close following cases is used to presents the results.  Such huge sample size taken from loop detectors will increase the results reliability as previous research used limited sample size. The results presented the cumulative distribution of drivers’ gap headway and suggested that the mean gap headway of drivers is about 1.1 s with standard deviation of 0.42 s.   The lane choice found to be significantly influencing the desired gap headway for speed higher than 70km/h only. The effect of the follower vehicle type of the desired gap headway was also examined and the results suggested that such effect is insignificant.  The findings of this paper are suggested to be used as inputs for traffic micro-simulation models.