Abstract
Understanding traffic characteristics and the behavior of drivers is crucial for motorway traffic managers and roadway operators. Time headway provides the comprehensive image of traffic stability and driver behavior under a wide range of traffic contexts. This paper discusses how traffic stability and driver behavior are affected by precipitation of several intensities. Mathematical modeling and comparison of time headway distributions under dry weather, light rain, medium rain, and heavy rain intensities were conducted with a gamma-generalized queuing model (gamma-GQM), and the trend of variations of the gamma-GQM parameters was analyzed. Relationships between the model parameters, traffic stability, and driver behavior were established when the parameters were plotted against hourly traffic volumes and average densities. The trend of variations of the four model parameters had a consistent distribution pattern under dry weather conditions. The variations of gamma-GQM parameters were slightly disturbed during light and heavy rainfall intensities. During medium rain conditions, the variation of gamma-GQM parameters was exceedingly disturbed. The results indicated that traffic characteristics and driver behavior were more inconsistent under medium rain than with all other intensities. The willingness of drivers to accept any kind of risk in following a vehicle largely varied during medium rain conditions. Speed variability provided an extra insight into the drivers' perception at different levels of rainfall intensities.
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