Speed Limit

Speed Limit

Road speed limits are used in most countries to regulate the speed of road vehicles. Speed limits may define maximum (which may be variable), minimum or no speed limit and are normally indicated using a traffic sign. Speed limits are commonly set by the legislative bodies of nations or provincial governments and enforced by national or regional police and / or judicial bodies.

The first maximum speed limit was the 10 mph (16 km/h) limit introduced in the United Kingdom in 1861. From 2005 to 2010, the highest posted speed limit was 160 km/h (99 mph) in Abu Dhabi, although this was reduced to 140 km/h (87 mph) in 2011. However, some roads have no speed limit for certain classes of vehicles. Best known are Germany's less congested Autobahns where automobile drivers have no mandated maximum speed. Measurements from the German State of Brandenburg in 2006 show average speeds of 137 km/h (85 mph) on 4-lane sections, and 142 km/h (88 mph) on 6-lane sections, without mandatory speed limits. Rural areas on the Isle of Man, the Indian states of Andhra Pradesh and Maharashtra also lack speed limits, but speeds are lower when measured on those lower design roads.

Speed limits are usually set to attempt to cap road traffic speed; there are several reasons for wanting to do this. It is often done with an intention to improve road traffic safety and reduce the number of road traffic casualties from traffic collisions. In their World report on road traffic injury prevention report, the World Health Organization (WHO) identify speed control as one of various interventions likely to contribute to a reduction in road casualties. (The WHO estimated that some 1.2 million people were killed and 50 million injured on the roads around the world in 2004.) Speed limits may also be set in an attempt to reduce the environmental impact of road traffic (vehicle noise, vibration, emissions), and to satisfy local community wishes. Some cities have reduced limits to as little as 30 km/h (19 mph) for both safety and efficiency reasons.

In situations where the natural road speed is considered too high, notably on urban areas where speed limits below 50 km/h (31 mph) are used then traffic calming is often also used. For some classes of vehicle speed limiters may be mandated to enforce compliance.

Since they have been introduced, speed limits have been opposed from various sources; including motoring advocacy groups, anti-motoring groups and others who either consider them to be irrelevant, set too low or set too high.