In Sustainably Safe roads have been designated in such a way that through car traffic is concentrated on motorways and other arterial roads. In areas with residential, shopping or work functions through traffic is discouraged and a maximum speed of 30 km/h is ensured by speed-reducing infrastructure like speed bumps, road narrowing et cetera. The number of accidents with injuries falls by approximately 25% on average when a residential area with a 50 km/h speed limit is redesigned as such a ‘zone 30’. These zones also positively affect quality of life, as regards noise levels, ease of crossing a road and emissions. According to the Sustainably Safe requirements residential areas should be as large as possible, but 200 hectares is the largest feasible surface area. A road structure of the ‘limited access’ type proves to be most appropriate for a 30 km/h area.