Speed limit

[4] Speed limits and safety distance are poorly enforced in the UAE, specifically on the Abu Dhabi to Dubai motorway – which results in dangerous traffic, according to a French government travel advisory.

On highways, unmarked speed bumps and drifting sand create additional hazards", according to a travel advisory issued by the U.S. State Department.

[7] Authorities may also set speed limits to reduce the environmental impact of road traffic (vehicle noise, vibration, emissions) or to enhance the safety of pedestrians, cyclists, and other road-users.

For example, a draft proposal from Germany's National Platform on the Future of Mobility task force recommended a blanket 130 km/h (81 mph) speed limit across the Autobahnen to curb fuel consumption and carbon emissions.

In 1652, the American colony of New Amsterdam passed a law stating, "No wagons, carts or sleighs shall be run, rode or driven at a gallop".

[12] The 1832 Stage Carriage Act introduced the offense of endangering the safety of a passenger or person by "furious driving" in the United Kingdom (UK).

[16] The Locomotives on Highways Act 1896, which raised the speed limit to 14 mph (23 km/h) is celebrated by the annual London to Brighton Veteran Car Run.

He shall slow down and if necessary stop whenever circumstances so require, and particularly when visibility is not excellent.Most legal systems expect drivers to drive at a safe speed for the conditions at hand, regardless of posted limits.

Other qualifying conditions include driving through fog, heavy rain, ice, snow, gravel,[29] or when drivers encounter sharp corners, a blinding glare,[30] darkness, crossing traffic,[31] or when there is an obstructed view of orthogonal traffic—such as by road curvature, parked cars, vegetation, or snow banks—thus limiting the Assured Clear Distance Ahead (ACDA).

[68] In Germany, the first known experiments with variable speed limit signs took place in 1965 on a 30-kilometre (19 mi) stretch of German motorway, the A8 between Munich and the border city of Salzburg, Austria.

Modern motorway control systems can work without human intervention using various types of sensors to measure traffic flow and weather conditions.

[71] More typically, variable speed limits are used on remote stretches of highway in the United States in areas with extreme changes in driving conditions.

[72] For example, variable limits were introduced in October 2010 on a 52-mile (84 km) stretch of Interstate 80 in Wyoming, replacing the winter season speed reduction from 75 to 65 mph (121 to 105 km/h) that had been in place since 2008.

[72][77] As a response to fog-induced chain-reaction collisions involving 99 vehicles in 1990, a variable speed limit system covering 19 miles (31 km) of Interstate 75 in Tennessee was implemented in fog-prone areas around the Hiwassee River.

[79] In 2016, the Oregon Department of Transportation installed a variable speed zone on a 30 mi (48 km) stretch of Interstate 84 between Baker City and Ladd Canyon.

Initial results suggested savings in journey times, smoother-flowing traffic, and a decrease in the number of crashes; the scheme was made permanent in 1997.

The first installation was on the Ngauranga Gorge section of the dual carriageway on State Highway 1, characterized by steep terrain, numerous bends, high traffic volumes, and a higher than average accident rate.

[23] In 2012, in Europe, 62% of people supported the idea of setting up speed-limiting devices,[23] with adequate tolerance levels in order to limit driver confusion.

[115] The city of Munich has adopted self-explaining roads: roadway widths, intersection controls, and crossing types have been harmonized so that drivers assume the speed limit without a posted sign.

[116] To be effective and abided by, the speed limits need to be perceived as credible; they should be reasonable regarding factors such as how well the driver can see ahead and to the sides on a particular road.

[133] Zones where speeds are set at 30 km/h (or 20 mph) are gaining popularity[134] as they are found to be effective at reducing crashes and increasing community cohesion.

Speed limits are set primarily to balance road traffic safety concerns with the effect on travel time and mobility.

[146] Finally, exceeding the posted limit may not be a remarkable factor in the crash analysis as there are roadways where virtually all motorists are in technical violation of the law.

In 2018, an IRTAD WG published a document which recommended maximum speed limits, taking into account forces the human body can tolerate and survive.

The United States instituted a National Maximum Speed Law of 55 mph (89 km/h), as part of the Emergency Highway Energy Conservation Act, in response to the 1973 oil crisis to reduce fuel consumption.

[153] According to a report published in 1986 by The Heritage Foundation, a Conservative advocacy group, the law was widely disregarded by motorists and hardly reduced consumption at all.

For example, automated camera enforcement has been criticised by motoring advocacy groups including the Association of British Drivers, and the German Auto Club (ADAC).

There are two basic designs for speed limit signs: the Vienna Convention on Road Signs and Signals specifies a white or yellow circle with a red border, while the Manual on Uniform Traffic Control Devices (MUTCD) published by the United States Federal Highway Administration specifies a white rectangle with the legend SPEED LIMIT.

Variations on the MUTCD design are used in Canada, Guam, Liberia, Puerto Rico,[176] the mainland United States, the U.S. Virgin Islands.

In the European Union, large signposts showing the national (maximum) speed limits of the respective country are usually erected immediately after border crossings, with a repeater sign some 200 to 500 m (660 to 1,640 ft) after the first.