This study assesses the sufficiency of Ajzen's (1985) theory of planne
d behaviour in predicting intentions to commit each of three driving v
iolations involving poor lane discipline: cutting across traffic to le
ave a motorway; weaving in and out of two lanes of slow-moving traffic
; and overtaking on the inside. Behavioural intention was predicted re
asonably well by the three main constructs of the theory of planned be
haviour. However, the addition of measures of anticipated regret and m
oral norm substantially improved prediction in each case, suggesting t
hat personal normative influence is an important factor in shaping int
entions to perform behaviours that are antisocial or socially controve
rsial. The development of a belief-based measure of perceived behaviou
ral control is also considered.