Speed limits and vehicle accidents in built-up areas: The impact of 30 km/h zones

Vehicle accidents represent an important source of externalities from driving. Using a detailed dataset on accident location and characteristics in Switzerland, we estimate the effect of switching from a 50 km/h speed limit to a 30 km/h limit on the probability of vehicle accident injuries. After an initial country-wide analysis, we exploit the quasi-experimental variation of the timing of introduction of 30 km/h zones in the municipality of Basel, using a difference in differences strategy. We find a significant reduction in accident severity due to lower speed limits, and substantial heterogeneities based on the circumstances of the accident.