BACKGROUND This study examines short- and long-run effects of a new-stricter-road traffic law on traffic accident-related fatalities in the Czech Republic. The law introduced tougher punishments through the introduction of a demerit point system and a manifold increase in fines, together with augmented authority of traffic police. METHODS Identification is based on difference-in-differences methodology, with neighbouring countries serving as a control group. RESULTS There was a sharp, 33.3%, decrease in accident-related fatalities during the first three post-reform months. This translates into 127 saved lives (95% confidence interval: 51, 204). The decline was, however, temporary; the estimates of the effects going beyond the first year are around zero. Unique data on traffic police activity reveal that police resources devoted to traffic law enforcement gradually declined. CONCLUSIONS Tougher penalties have significant, but often short-lived effects. Weaker enforcement in the aftermath of such reforms may explain the absence of long-run effects.