Speed limit

A road speed limit is the maximum speed allowed by law for road vehicles. Speed limits are commonly set and enforced by the legislative bodies of nations or provincial governments, such as countries within the world.

In addition to setting a maximum speed limit, most governments also enforce speed limits which are relative to the driving conditions experienced; that is, drivers should adjust their maximum speed when driving in fog, heavy rain, or other similar conditions. For example, the California Civil Code 22350 states that "No person shall drive a vehicle upon a highway at a speed greater than is reasonable... and in no event at a speed which endangers the safety of persons or property." This "basic rule", or similar legal language, applies even where no maximum speed limit is in place (such as formerly in the U.S. state of Montana). Some roads also have "minimum speed limits", where slow speeds are considered to impede traffic flow or be dangerous.

The first speed limit was the 10 mph limit introduced by the Locomotive Act of 1861 (or "Red Flag Act") in the United Kingdom (automobiles were in those days termed “light locomotives”). In 1865, the revised Locomotive Act reduced the speed limit to 4 mph in the country and 2 mph in towns. The 1865 Act required a man with a red flag or lantern to walk 60 yards ahead of each vehicle, enforce a walking pace, and warn horse riders and horse drawn traffic of the approach of a self-propelled machine. The replacement of the "Red Flag Act" by the Locomotive Act of 1896, and the increase of the speed limit to 14 mph has been commemorated each year since 1927 by the London to Brighton Veteran Car Run.

Nepal, the Isle of Man and the Indian state of Uttar Pradesh are the only places in the world that do not have a general speed limit. In Germany, some (but not all) sections of the autobahn (motorway) network also remain free from speed limits. Not including public roads which do not have a legal speed limit, the highest speed limit in the world is 160 km/h (99 mph), which has been experimentally applied on selected test stretches in Austria and the United Arab Emirates.