Traffic crash pattern modification as a result of a 30 km/h zone implementation. A case study in Turin (Italy)

The strategy of 30 km/h zones, referred to in the international context as "traffic calming" measures, serves to safeguard pedestrians, cyclists and motorcyclists, collectively referred to as “vulnerable road users” (VRU). Its main function is to compel drivers to observe a maximum speed limit of 30 km/h. However, urban infrastructure transformations modify traffic collision patterns and the involvement of road users, with a spatial temporal redistribution of events. This work seeks to study the effects on collision distribution resulting from the introduction of a 30 km/h zone to the Mirafiori Nord area in the city of Turin in late 2008. Collision frequencies, based on data provided by the Italian National Institute of Statistics (ISTAT), were evaluated over the period 2006-2016. Road traffic collisions involving both VRU and motorized users (“noVRU”) were taken into account. Decreases in collision frequency were found for noVRU related crashes, while the VRU crash rate remained essentially unchanged with only minor fluctuations consistent with the regression to the mean phenomenon. The countermeasures, which sought to protect VRU, were however very effective for noVRU. As the effects of each structural modification spill over into neighboring areas, the analysis of collision frequency was extended to a study area greater than the one in which the 30 km/h zone was realized. In fact, due to the migration of events, the reduction in the collision frequency in the speed restricted zone was accompanied by an increase in the same frequency in the immediate surrounding area.