Abstract
The role of deterrence in economics focuses primarily on changing the individual's perceived expected cost of engaging in an illegal activity and the primary impetus of deterrence in law enforcement is to increase the perceived certainty of apprehension and punishment. Using data from the Australian State of Queensland, this paper examined the deterrent effects of increasing the level of police presence and the apprehension rate and found that increasing either the number of random breath tests performed or the proportion of drivers tested positive for drink driving significantly reduced the number of serious crashes on the roads. (Author/publisher).