The Intended and Unintended Effects of Drunk Driving Policies

Taking advantage of merged administrative data, we estimate the intended and unintended effects of two public policies aimed at combating driving under influence (DUI) of alcohol in Taiwan: the three-month-long campaign of random sobriety checkpoints in mid-2012, and the legal reform carried out in mid-2013 leading to much harsher punishments for DUI offenders. Our study gives rise to several important findings: (i) The checkpoint campaign substantially reduced DUI deaths and injuries, and the effect persisted after the campaign ended; (ii) the campaign also had a strong spillover effect of reducing non-DUI deaths and injuries, and this unintended effect was four times the size of the intended effect on DUI cases; (iii) these effects were not driven by social pressure or self-awareness arising from the intensive media coverage taking place at the same time; and (iv) there was little response to either policy among repeat DUI offenders and those who caused serious injuries.