Evidence-based policy on road safety: the effect of the demerit points system on seat belt use and health outcomes.

Objective: To assess the effect of a demerit points system, introduced in Italy in July 2003, on the prevalence of seat belt use (intermediate outcome) and the number of road traffic deaths and injuries (health outcomes).

Design: Pre- and post-intervention regional observational study for seat belt investigation (April 2003, October 2004); national time-series analysis of road traffic deaths and injuries between 1999 and 2004 for health outcomes.

Setting: Veneto region, Italy.

Participants: 19,551 drivers, 19,057 front passengers and 8,123 rear passengers estimated to be aged over 11 years were included in the investigation into seat belt use. 38,154 fatalities and 1,938,550 injured subjects were examined for the time-series analysis.

Interventions: Demerit points system.

Main Outcome Measures: The proportions of drivers and front and rear passengers observed to be using seat belts before and after the intervention; estimates of lives and injuries saved through the implementation of a penalty points system.

Results: The demerit points system was followed by an increase in observed seat belt use of 51.8% (95% confidence interval 48.7% to 54.9%) among drivers, of 42.3% (95% confidence interval 39.2% to 45.5%) among front passengers and of 120.7% (95% confidence interval 99.4% to 144.3%) among rear passengers. It is estimated that 1,545 (95% confidence interval 1387 to 1703; p<0.0001) deaths and 91,772 (95% confidence interval 67,762 to 115,783; p<0.0001) injuries were prevented in the 18 months after the introduction of the legislation, i.e. an 18% reduction (1545/8570) in fatalities and a 19% reduction (91,772/473,048) in injuries.

Conclusions: The demerit points system is effective both in encouraging drivers and passengers to adhere to the law and in terms of health outcomes, substantially contributing to road safety.