Sanctions are considered to be an essential element of effective enforcement. The possibility of a sanction ascertains the deterrent effect of enforcement. Despite the essential role, the effects of sanctions are still fairly unknown. It has been argued that in order to be effective, sanctions must be based on certainty and be imposed with minimal delay . The argument of immediacy of punishment is deduced from the scientific field of learning theories and behaviouristic animal experiments. In practical terms, there is no evidence that instantly imposed sanctions (within a few days) are more effective than sanctions imposed with a short delay of one or several weeks.
Another issue is the height of the fine. An overview of the literature  did not reveal consistent results on the effects of increasing punishment severity. More recently, Elvik and Christensen  evaluated the effects of increase of fixed speed and seat belt penalties in Norway. They could not find an effect on speeding. For seat belt wearing, however, they found an increase in wearing rate. The authors suggest that the positive effect of penalties on seat belt use may partly be due to the increase in seat belt enforcement in Norway in the same period. The absence of any effect on speeding is attributed to the fact that the objective risk of apprehension is quite low on most parts of the road network. These findings suggest that increasing penalties may improve compliance with traffic rules, but only when the risk of apprehension is high. When the risk of apprehension is low, increasing fixed penalties does not make a noticeable difference for deterrence.
Although, as a general rule, the use of sanctions is necessary to achieve compliance, alternatives should much more be considered. In a Finnish experiment, it has been shown that stopping drivers and issuing them a speeding ticket was not more effective than a warning letter sent by mail . Both a warning letter and a fine resulted in decreased speeds of sanctioned drivers of 9 to 10 km/h for a period of at least three months.
A survey study in the UK  indicated that drivers respond differently to speeding fines. Three separate groups were identified, whose size could be estimated:
- Those who now drive more slowly, including both at camera sites and elsewhere: 41 - 56%
- Those who now only slow down at camera sites, but not elsewhere: 30 - 32%
- Those not doing either: 14 - 15%
Thus, approximately one half the respondents were more speed sensitive soon after receipt of punishment, one third were more camera sensitive, and one sixth were neither. Punishment, in the form of a £60 fine and 3 penalty points, had a specific deterrent function for some drivers, but left others unremediated.
To increase its effectiveness, speed enforcement must be supported by setting safe and credible speed limits, by publicity, by legislation facilitating effective enforcement, and by appropriate sanctions.
Alternatives to negative sanctions (such as warning letters, educational courses, speed limiters) and the further development of these sanctions merit serious consideration of authorities, practitioners and researchers.