Aspects of driver behaviour in main road traffic streams

Abstract

Studies of composite headway models and platooning are reviewed and further results on time headways distribution are given. It is suggested that a three-population model is more satisfactory than a two-population model when short headways are of primary importance. Platoons were shown to occur randomly and the distribution of platoon sizes can be closely represented by a modified geometric distribution. It was also found that the distribution of headways in platoons was independent of speed at a given site, and members of platoons were shown to follow too closely in terms of the Highway Code advice; this close following behaviour was shown to be relatively greater at higher speeds. Observations showed that the deceleration behaviour of driver in a major road approaching a rural T-junction was affected by the T-junction (a) being unoccupied, (b) having vehicles waiting to cross and (c) having vehicles actually crossing. The results in case (a) were used to deconvolute the effects due to background in cases (b) and (c). Empirical results on the relationship between a measure of deceleration and other factors are presented. The deconvoluted values together with other observed data were used as input into a conflict simulation model. The output of the model consists of the number of precautionary and severe model conflicts to be expected in various circumstances. Results on driver gap-acceptance behaviour in adverse weather conditions at T-junctions are presented in appendix. No evidence of more cautious behaviour in wet weather was found.