The speed choice for 30 km/h zones is primarily from road safety considerations. A crash is rarely fatal at an impact speed below 30 km/h. This is also the case for crashes between a car and a vulnerable, unprotected cyclist or pedestrian. At an impact speed of 30 km/h more than 95% of the pedestrians survive a crash with a passenger car; at an impact speed of 50 km/h approximately 85% of the pedestrians survive such a crash (; see also SWOV Fact sheet Speed and speed management; and Figure 1). Therefore, it is relatively safe for slow and motorized traffic to mix at speeds up to 30 km/h. In addition, a 30 km/h limit has a positive effect on the quality of life in these areas: the sound level of the traffic is lower, crossing the street is easier, and emissions are lower.
Figure 1. The relationship between impact speed and fatality risk of pedestrians in crashes with a passenger car according to some recent studies (in: Rosén et al., 2011 ).