20 mph: lower speeds, better streets
The risk of serious injury or death to pedestrians or cyclists increases disproportionately as speeds increase. A pedestrian hit at 40mph has a 31% chance of death; hit at 30mph and that risk falls to 7%; at 20mph the risk is negligible.
20mph should be the standard speed limit for most streets in built-up areas. Local authorities should decide which roads have such a strategic traffic function that higher speeds are required.
20 mph is a much safer speed - a study into 20 mph zones in London found that casualties fell by an average of 42%.
Lower speed limits are also linked with increased cycling and walking. In the Netherlands 30kmh (18.5mph) covers 75% of the residential street network and is deemed a safe speed for cyclists, pedestrians and light vehicles to mix.
20mph as the standard urban speed limit has become more and more widespread in recent years, with many towns and cities adopting this approach. Portsmouth, Oxford and Newcastle are just a few of the areas that are returning speeds to 20mph.