The speed of a vehicle should be entirely under the control of the driver. Proceeding at a speed that is excessive in view of the traffic conditions is a common contributory cause of accidents.
A Dutch study has shown that reducing the speed limit by 10 percent leads to a 50 percent drop in accidents. A report by the European Transport Safety Council includes a rough calculation that a speed reduction of just 5 kph could save 11,000 lives in the EU and prevent 180,000 injuries per year.