Investigating the effect of 30 km/h on neighborhood traffic safety perceptions- A three-wave repeated cross-sectional study in the Netherlands

Introduction Urban 30 km/h speed limits are increasingly implemented, potentially affecting perceived traffic safety. We assess how exposure to streets transitioning from 50 km/h to 30 km/h affects residents' traffic safety perceptions. Methods We analyzed repeated cross-sectional data from two administrative surveys (N = 4968 and 5146) spanning 2015, 2017, and 2019. Exposure was defined as living within 400m of fifty-six streets across Rotterdam where speed limits reduced from 50 km/h to 30 km/h. Controls lived within 400m of streets undergoing future reductions. Using a difference-in-differences approach, we compared the probability of reporting seven binary outcomes on traffic-related safety, environmental annoyance, and pedestrian and cyclist safety between exposed and control individuals before and after speed limit reductions. We stratified the intervention group in tertiles of intervention street proportion within 400m Euclidian buffers, and additionally cross-sectionally investigated the association between dosage of intervention street density and perceived safety outcomes. Results No significant differences were observed between residents living near intervention streets and those near control streets. Small, non-significant improvements were found for perceived speeding (−4.6 percentage points (%pt) [95%CI -10.5,1.3]) and aggressive driving (−5.8%pt [95%CI -11.8,0.2]), while bicycle path safety showed a non-significant effect in the opposite direction (6.3%pt [95%CI -0.07,12.6]). The stratified analysis showed a non-significant improvement in the highest exposure tertile of sidewalk safety, but was inconclusive for the other indicators. Dosage findings indicated that a 5% increase in nearby intervention streets was associated with a lower probability of perceived speeding (−1.9%pt [95%CI −3.1,−0.6]), aggressive driving behavior (−1.5%pt [95%CI -3.1,0.04]) and increased bicycle path safety (−1.6%pt [95%CI -3.3,0.04]). Conclusion Reducing urban speed limits to 30 km/h may have contributed to small, non-significant improvements in perceived traffic safety. The study may have been underpowered to detect statistically significant effects. Future studies should examine intended and unintended effects of traffic safety interventions.