Vehicle impact speed is the most influential factor attributing to the severity of injuries at the time of a collision/crash. Slower vehicle speed collision may result in less severe injuries whereas higher vehicle speed collisions can result in fatalities. For instance, if a pedestrian is involved in a collision where the vehicle is traveling at 20 miles per hour (mph), the pedestrian has a 90% survival rate. However, if the vehicle is traveling at 40 mph, the pedestrian survival rate reduces to 50%. Small reductions in vehicle speed can have important safety impacts.
In addition, vehicles traveling at slower speeds emit less noise, which results in a more pleasant environment, especially for individuals outside in close proximity to the roadway. Slower vehicle speeds are more closely associated with walkable, livable communities.
San Francisco Vision Zero Action Plan 2015