Wikipedia Reference Information
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 States within the USA.
In addition to setting a maximum speed limit, most governments also enforce speed limits which are relevative to the driving conditions experienced, for instance drivers should adjust their maximum speed when driving in fog or heavy rain. 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 whether or not maximum speed limits are in place (such as formerly in the US 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.
Some countries, Germany for example, have no speed limit on some of their roads. Not including public roads which do not have a legal speed limit, the highest speed limit in the world is 160 km/h (100 mph), which has been experimentally applied on selected test stretches in Austria and the United Arab Emirates.
The complete, up-to-date and editable article about Speed Limit can be found at Wikipedia: Speed Limit