Speed limit
Overview
 
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
Traffic sign
Traffic signs or road signs are signs erected at the side of roads to provide information to road users. With traffic volumes increasing over the last eight decades, many countries have adopted pictorial signs or otherwise simplified and standardized their signs to facilitate international travel...

. Speed limits are commonly set by the legislative bodies of nations or provincial governments and enforced by national or regional police
Police
The police is a personification of the state designated to put in practice the enforced law, protect property and reduce civil disorder in civilian matters. Their powers include the legitimized use of force...

 and / or judicial bodies.

The first maximum speed limit was the 10 mph (4 m/s) limit introduced in the United Kingdom
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...

 in 1861.
Encyclopedia
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
Traffic sign
Traffic signs or road signs are signs erected at the side of roads to provide information to road users. With traffic volumes increasing over the last eight decades, many countries have adopted pictorial signs or otherwise simplified and standardized their signs to facilitate international travel...

. Speed limits are commonly set by the legislative bodies of nations or provincial governments and enforced by national or regional police
Police
The police is a personification of the state designated to put in practice the enforced law, protect property and reduce civil disorder in civilian matters. Their powers include the legitimized use of force...

 and / or judicial bodies.

The first maximum speed limit was the 10 mph (4 m/s) limit introduced in the United Kingdom
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...

 in 1861. From 2005 to 2010, the highest posted speed limit was 160 km/h (99 mph) in Abu Dhabi
Abu Dhabi
Abu Dhabi , literally Father of Gazelle, is the capital and the second largest city of the United Arab Emirates in terms of population and the largest of the seven member emirates of the United Arab Emirates. Abu Dhabi lies on a T-shaped island jutting into the Persian Gulf from the central western...

, 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
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...

's less congested Autobahns where automobile drivers have no mandated maximum speed. Measurements from the German State of Brandenburg
Brandenburg
Brandenburg is one of the sixteen federal-states of Germany. It lies in the east of the country and is one of the new federal states that were re-created in 1990 upon the reunification of the former West Germany and East Germany. The capital is Potsdam...

 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
Isle of Man
The Isle of Man , otherwise known simply as Mann , is a self-governing British Crown Dependency, located in the Irish Sea between the islands of Great Britain and Ireland, within the British Isles. The head of state is Queen Elizabeth II, who holds the title of Lord of Mann. The Lord of Mann is...

, the Indian states of Andhra Pradesh
Andhra Pradesh
Andhra Pradesh , is one of the 28 states of India, situated on the southeastern coast of India. It is India's fourth largest state by area and fifth largest by population. Its capital and largest city by population is Hyderabad.The total GDP of Andhra Pradesh is $100 billion and is ranked third...

 and Maharashtra
Maharashtra
Maharashtra is a state located in India. It is the second most populous after Uttar Pradesh and third largest state by area in India...

 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)
World Health Organization
The World Health Organization is a specialized agency of the United Nations that acts as a coordinating authority on international public health. Established on 7 April 1948, with headquarters in Geneva, Switzerland, the agency inherited the mandate and resources of its predecessor, the Health...

 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.)World Heath Organisation (2004) p. foreword, "In high-income countries, an established set of interventions have contributed to significant reductions in the incidence and impact of road traffic injuries. These include the enforcement of legislation to control speed and alcohol consumption, mandating the use of seat-belts and crash helmets, and the safer design and use of roads and vehicles." Speed limits may also be set in an attempt to reduce the environmental impact of road traffic (vehicle noise, vibration, emissions), to reduce fuel use and to satisfy local community wishes.

Speed limits are used to reduce the differences in vehicle speeds by drivers using the same road at the same time which increases safety. In situations where the natural road speed is considered too high, notably on urban areas where speed limits below 50 km/h (31.1 mph) are used then traffic calming
Traffic calming
Traffic calming is intended to slow or reduce motor-vehicle traffic in order to improve the living conditions for residents as well as to improve safety for pedestrians and cyclists. Urban planners and traffic engineers have many strategies for traffic calming...

 is often also used. For some classes of vehicle speed limiter
Speed limiter
A speed limiter is a governor used to limit the top speed of a vehicle. For some classes of vehicle and in some jurisdictions they are a statutory requirement, for some other vehicles the manufacturer provides a non-statutary system which may be fixed or programmable by the driver.-Mopeds:Mopeds in...

s 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.

History

The first speed limit legislation was created in the United Kingdom with the Locomotive Acts (automobiles were in those days termed “light locomotives”). The 1865 Act introduced a UK speed limit
Road speed limits in the United Kingdom
Road speed limits in the United Kingdom are used to define the maximum legal speed limit for road vehicles using public roads in the UK, and are one of the measures available to attempt to control traffic speeds. The speed limit in each location is indicated on a nearby traffic sign or by the...

 of 10 mph (4 m/s) which was then reduced to 4 mph (6 km/h) in the country and 2 mph (3 km/h) in towns by the 1865 Act (the 'red flag act'). The first person to be convicted of speeding is believed to be Walter Arnold of East Peckham
East Peckham
East Peckham is a village in Kent, England, made up of nine hamlets and situated about east of Tonbridge on the River Medway. It was the centre for the hop growing industry in Kent and is still home to the Hop Farm which has the world's largest collection of Oast Houses.-History:The Domesday entry...

, Kent, who on 28 January 1896 was fined for speeding at 8 mph (12.9 km/h). He was fined 1 shilling plus costs. Passage of the Locomotives on Highways Act 1896
Locomotives on Highways Act 1896
The Locomotives on Highways Act 1896 removed the strict rules and UK speed limits that were included in the earlier Locomotive Acts which had greatly restricted the adoption of motorised vehicles in the United Kingdom...

, which raised the speed limit to a "furious" pace of 14 mph is celebrated to this day by the annual London to Brighton Veteran Car Run
London to Brighton Veteran Car Run
The London to Brighton Veteran Car Run is the longest-running motoring event in the world. The first run was in 1896, and has taken place most years since then. To qualify, the cars must have been built before 1905...

.

Regulations

All countries use metric
Metric system
The metric system is an international decimalised system of measurement. France was first to adopt a metric system, in 1799, and a metric system is now the official system of measurement, used in almost every country in the world...

 units (kilometres per hour
Kilometres per hour
The kilometre per hour is a unit of speed, expressing the number of kilometres traveled in one hour. The unit symbol is km/h or km·h−1....

), except for the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...

 and the United Kingdom, where speed limits are given in miles per hour
Miles per hour
Miles per hour is an imperial unit of speed expressing the number of statute miles covered in one hour. It is currently the standard unit used for speed limits, and to express speeds generally, on roads in the United Kingdom and the United States. It is also often used to express the speed of...

.

Basic rule: reasonable speed

Drivers are required to drive at a safe speed for conditions. In the United States this requirement is referred to as the basic rule, but more generally in Britain and elsewhere in common law as the reasonable man requirement. Lower speed may be required due to fog, heavy rain, and pavement conditions such as freezing or gravel, or where they are not able to stop in the line of sight. California Vehicle Code section 22350 is typical; it 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".

Maximum speed limits

Most public roads in most countries have a legally assigned numerical maximum speed limit which applies on all roads unless otherwise stated; lower speed limits are often shown on a sign at the start of the restricted section although the presence of streetlights, or the physical arrangement of the road may sometimes also be used instead. A posted speed limit may only apply to that road or to all roads beyond the sign that defines them depending on local laws. In the European Union
European Union
The European Union is an economic and political union of 27 independent member states which are located primarily in Europe. The EU traces its origins from the European Coal and Steel Community and the European Economic Community , formed by six countries in 1958...

, large signposts showing the national (default) speed limits of the respective country are usually erected immediately after border crossing
Border control
Border controls are measures used by a country to monitor or regulate its borders.The control of the flow of many people, animals and goods across a border may be controlled by government Customs services. Security is enforced by various kinds of Border Guards and Coast Guards...

s, with a repeater sign some 200 metre after the first sign. Some places provide an additional "speed zone ahead" ahead of the restriction and speed limit reminder signs may appear at regular intervals which may be painted on the road surface.

Signs are normally placed on both sides of the road and in some places there are small (less than 1/4 the size of the sign) rectangular orange reflector flags attached to both upper right corners of both signs. The speed limit sign marking the new speed zone may also have the orange flags.

Signage in many countries, especially in Europe, conforms to the Vienna Convention on Road Signs and Signals
Vienna Convention on Road Signs and Signals
The Vienna Convention on Road Signs and Signals is an international treaty designed to increase road safety and aid international road traffic by standardising the signing system for road traffic in use internationally.This convention was agreed upon by the United Nations Economic and Social...

 using black text with a red circle on a white background. In the United States, the signs are usually rectangular with the words "SPEED LIMIT" and the values in black on a white background. The U.S. Federal Highway Administration's Manual on Uniform Traffic Control Devices
Manual on Uniform Traffic Control Devices
The Manual on Uniform Traffic Control Devices is a document issued by the Federal Highway Administration of the United States Department of Transportation to specify the standards by which traffic signs, road surface markings, and signals are designed, installed, and used...

 provides guidelines for the appearance of speed limit signs. Canada has similar signs bearing the legend "MAXIMUM" and in km/h instead of mph. "Maximum" is used instead of "Speed Limit" because it has similar meanings in English and French. Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...

n signs are rectangular but have a red circle like the conventional signs.

Posted maximum speeds are normally based on ideal driving conditions.

Minimum speed limits

Some roads also have "minimum speed limits", where slow speeds can impede traffic flow or be dangerous and on motorways slower vehicles such as horse drawn vehicles, bicycles and mopeds can be banned, e.g. in the United Kingdom.

Signs often use blue circles based on the obligatory signs of the Vienna Convention on Road Signs and Signals. A Japanese minimum speed sign has the same design as a maximum speed sign but with a horizontal line below the number. In the United States of America, they are also identical to their respective maximum speed limit signs with the exception of the text "MINIMUM SPEED".

Variable speed limits

In 1965, the first known experiments with variable speed limit signs took place on a 30 km stretch of German motorway A8
Bundesautobahn 8
is an autobahn in southern Germany that runs 497 km from the Luxembourg A13 motorway at Schengen via Neunkirchen, Pirmasens, Karlsruhe, Stuttgart, Ulm, Augsburg and Munich to the Austrian West Autobahn near Salzburg....

 between Munich
Munich
Munich The city's motto is "" . Before 2006, it was "Weltstadt mit Herz" . Its native name, , is derived from the Old High German Munichen, meaning "by the monks' place". The city's name derives from the monks of the Benedictine order who founded the city; hence the monk depicted on the city's coat...

 and the border city of Salzburg
Salzburg
-Population development:In 1935, the population significantly increased when Salzburg absorbed adjacent municipalities. After World War II, numerous refugees found a new home in the city. New residential space was created for American soldiers of the postwar Occupation, and could be used for...

, Austria
Austria
Austria , officially the Republic of Austria , is a landlocked country of roughly 8.4 million people in Central Europe. It is bordered by the Czech Republic and Germany to the north, Slovakia and Hungary to the east, Slovenia and Italy to the south, and Switzerland and Liechtenstein to the...

. Mechanically variable message signs could display speeds of 60, 80 and 100 km/h, "danger zone" or "accident". Personnel monitored traffic using video technology, and manually controlled the signage. Beginning in the 1970s, more and more advanced traffic control systems were put into service. Modern motorway control systems can work without human intervention using various types of sensors to measure traffic flow and weather conditions. In 2009, 1300 km (807.8 mi) of German motorways were equipped with such systems.

In the late 1960s, heavily traveled portions of the New Jersey Turnpike
New Jersey Turnpike
The New Jersey Turnpike is a toll road in New Jersey, maintained by the New Jersey Turnpike Authority. According to the International Bridge, Tunnel and Turnpike Association, the Turnpike is the nation's sixth-busiest toll road and is among one of the most heavily traveled highways in the United...

 began using variable speed limit signs, in combination with variable message signs. Officials can adjust the speed limit according to weather, traffic conditions, and construction. More typically, variable speed limits are used on remote stretches of highway in the United States in areas with extreme changes driving conditions.http://ntl.bts.gov/lib/jpodocs/briefing/12164.pdf For example, variable limits were introduced in Oct 2010 on a 52-mile stretch of Interstate 80
Interstate 80
Interstate 80 is the second-longest Interstate Highway in the United States, following Interstate 90. It is a transcontinental artery running from downtown San Francisco, California to Teaneck, New Jersey in the New York City Metropolitan Area...

 in Wyoming
Wyoming
Wyoming is a state in the mountain region of the Western United States. The western two thirds of the state is covered mostly with the mountain ranges and rangelands in the foothills of the Eastern Rocky Mountains, while the eastern third of the state is high elevation prairie known as the High...

, replacing the winter season speed reduction from 75 to 65-mph that had been in place since 2008. Similarly, Interstate 90
Interstate 90
Interstate 90 is the longest Interstate Highway in the United States at . It is the northernmost coast-to-coast interstate, and parallels US 20 for the most part. Its western terminus is in Seattle, at Edgar Martinez Drive S. near Safeco Field and CenturyLink Field, and its eastern terminus is in...

 at Snoqualmie Pass
Snoqualmie Pass
Snoqualmie Pass is a mountain pass that carries Interstate 90 through the Cascade Range in the U.S. State of Washington. The elevation of the pass summit is , and is on the county line between Kittitas County and King County...

 and other mountain passes in Washington State variable speed limits are used to slow traffic in severe winter weather.http://ntl.bts.gov/lib/jpodocs/briefing/12164.pdf A response to fog-induced chain-reaction collisions involving 99 vehicles in 1990, a variable speed limit system covering 19 miles (30.6 km) of Interstate 75
Interstate 75
Interstate 75 is a major north–south Interstate Highway in the Great Lakes and Southeastern regions of the United States. It travels from State Road 826 and State Road 924 in Hialeah, Florida to Sault Ste. Marie, Michigan, at the Ontario, Canada, border...

 in Tennessee
Tennessee
Tennessee is a U.S. state located in the Southeastern United States. It has a population of 6,346,105, making it the nation's 17th-largest state by population, and covers , making it the 36th-largest by total land area...

 was implemented in fog-prone areas around the Hiwassee River
Hiwassee River
The Hiwassee River has its headwaters on the north slope of Rocky Mountain in Towns County in northern Georgia and flows northward into North Carolina before turning westward into Tennessee, flowing into the Tennessee River a few miles west of State Route 58 in Meigs County, Tennessee...

.

A variable speed limit was introduced on part of Britain's M25 motorway
M25 motorway
The M25 motorway, or London Orbital, is a orbital motorway that almost encircles Greater London, England, in the United Kingdom. The motorway was first mooted early in the 20th century. A few sections, based on the now abandoned London Ringways plan, were constructed in the early 1970s and it ...

 in 1995 (on the busiest 14 miles (23 km) section from junction 10 to 16. Initial results suggested savings in journey times, smoother-flowing traffic, as well as a fall in the number of crashes and the scheme was made permanent in 1997. However a 2004 National Audit Organization report noted that the business case was unproved; conditions at the site of the Variable Speed Limits trial were not stable before or during the trial, and the study was deemed neither properly controlled nor reliable. From December 2008 the upgraded section of the M1 between the M25 and Luton
Luton
Luton is a large town and unitary authority of Bedfordshire, England, 30 miles north of London. Luton and its near neighbours, Dunstable and Houghton Regis, form the Luton/Dunstable Urban Area with a population of about 250,000....

 will have the facility for variable speed limits. In January 2010 temporary variable speed cameras on the M1 between J25 and J28 were made permanent.

New Zealand
New Zealand
New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...

 introduced variable speed limits in February 2001. The first installation was on the Ngauranga Gorge
Ngauranga Gorge
The Ngauranga Gorge is in the Wellington Region of New Zealand. State Highway 1 runs through the gorge, a vital link between Wellington City and the Kapiti Coast and the main route north out of Wellington. It is 2 kilometres long and has a grade of approximately 8%...

 section of dual carriageway on State Highway 1 with steep terrain, numerous bends, high traffic volumes, and higher than average accident rate. The speed limit is normally 80 km/h.

In 2006, Austria
Austria
Austria , officially the Republic of Austria , is a landlocked country of roughly 8.4 million people in Central Europe. It is bordered by the Czech Republic and Germany to the north, Slovakia and Hungary to the east, Slovenia and Italy to the south, and Switzerland and Liechtenstein to the...

 undertook a short term experiment with a variable limit configuration that could increase statutory limits under the most favorable conditions, as well as reduce them. In June, a stretch of motorway was configured with variable speed limits could increase the general Austrian motorway limit of 130 kilometres per hour (81 mph) up to 160 kilometres per hour (99 mph). Then Austrian Transport Minister Hubert Gorbach
Hubert Gorbach
Hubert Gorbach is an Austrian politician and a member of the Alliance for the Future of Austria . Until April 2005, he was a leading member in the Freedom Party. Born in Vorarlberg, he was vice-governor of Vorarlberg until 2003.In 2003, he succeeded Herbert Haupt as Vice-Chancellor of Austria...

 called the experiment "a milestone in European transport policy-despite all predictions to the contrary"; however, the experiment was discontinued.

Roads without speed limits

Many roads without a maximum limit became permanently limited following the 1973 oil crisis
1973 oil crisis
The 1973 oil crisis started in October 1973, when the members of Organization of Arab Petroleum Exporting Countries or the OAPEC proclaimed an oil embargo. This was "in response to the U.S. decision to re-supply the Israeli military" during the Yom Kippur war. It lasted until March 1974. With the...

. For example, Switzerland
Switzerland
Switzerland name of one of the Swiss cantons. ; ; ; or ), in its full name the Swiss Confederation , is a federal republic consisting of 26 cantons, with Bern as the seat of the federal authorities. The country is situated in Western Europe,Or Central Europe depending on the definition....

 had no maximum restriction prior to 1973 on motorways and rural roads, but imposed a temporary 100 km/h (62 mph) maximum limit in quick response to higher fuel prices; the limit on motorways was increased to 130 km/h (81 mph) later in 1974.

Montana
Montana
Montana is a state in the Western United States. The western third of Montana contains numerous mountain ranges. Smaller, "island ranges" are found in the central third of the state, for a total of 77 named ranges of the Rocky Mountains. This geographical fact is reflected in the state's name,...

 and Nevada
Nevada
Nevada is a state in the western, mountain west, and southwestern regions of the United States. With an area of and a population of about 2.7 million, it is the 7th-largest and 35th-most populous state. Over two-thirds of Nevada's people live in the Las Vegas metropolitan area, which contains its...

 were the last remaining U.S. states relying exclusively on the basic rule, without a specific, numeric rural speed limit prior to the National Maximum Speed Law
National Maximum Speed Law
The National Maximum Speed Law in the United States was a provision of the 1974 Emergency Highway Energy Conservation Act that prohibited speed limits higher than . It was drafted in response to oil price spikes and supply disruptions during the 1973 oil crisis...

 of 1974. After repeal of Federal speed mandates in 1996, Montana was the only state to revert to rural daytime speed limit, beyond the Basic Rule. After the Montana Supreme Court decided that the Basic Rule was too vague and therefore violated the due process
Due process
Due process is the legal code that the state must venerate all of the legal rights that are owed to a person under the principle. Due process balances the power of the state law of the land and thus protects individual persons from it...

 requirement of the Montana Constitution
Montana Constitution
The Constitution of the State of Montana is the primary legal document providing for the self-governance of the U.S. State of Montana. It establishes and defines the powers of the three branches of the government of Montana, and the rights of its citizens...

, Montana's legislature imposed a 75 mph (34 m/s) limit on rural freeways in 1999, although the same wording in the basic rule remains.

Australia's Northern Territory
Northern Territory
The Northern Territory is a federal territory of Australia, occupying much of the centre of the mainland continent, as well as the central northern regions...

 had no blanket speed limits outside major towns until January 2007 when a general rural speed limit of 110 km/h (68 mph) was introduced; four major highway have higher 130 km/h (81 mph) zones. The per-capita fatality rate in 2006 was the highest in the OECD and twice the Australian average. In 2009, the opposition party unsuccessfully sought the removal of the 130 km/h limits on three out of the four highways where it applied, arguing that total fatalities in the Northern Territory had increased significantly during the first two years of the speed limit. In argument against the motion, the government provided more detailed statistics showing a reduction in fatalities along the highways where 130 km/h limits were introduced.

The Isle of Man
Isle of Man
The Isle of Man , otherwise known simply as Mann , is a self-governing British Crown Dependency, located in the Irish Sea between the islands of Great Britain and Ireland, within the British Isles. The head of state is Queen Elizabeth II, who holds the title of Lord of Mann. The Lord of Mann is...

 has no speed limit on many rural roads; a 2004 proposal to introduce a general speed limits 60 mph and of 70 mph on Mountain Road
A18 road (Isle of Man)
The A18 Snaefell Mountain Road or Mountain Road is 15.30 miles long road in the Isle of Man and is a primary road which connects Douglas with Ramsey. The A18 Mountain Road is part of Snaefell Mountain Course or Mountain Course is a road-racing circuit used for the Isle of Man TT and Manx Grand...

 for safety reasons were not progressed following consultation.
Measured travel speeds on the island are relatively low.

As of 2008, 52% of the German autobahns
German Autobahnen
The German autobahns are the nationally coordinated motorway system in Germany. In German, they are officially called Bundesautobahn , which translates as federal expressways...

 have only advisory limits (Richtgeschwindigkeit), 15% have temporary speed limits due to weather or traffic conditions and 33% have permanent speed limits. The length of speed-unrestricted autobahns slowly expanded after the opening of the East German borders in November 1989. Prior to German reunification
German reunification
German reunification was the process in 1990 in which the German Democratic Republic joined the Federal Republic of Germany , and when Berlin reunited into a single city, as provided by its then Grundgesetz constitution Article 23. The start of this process is commonly referred by Germans as die...

 in 1990, accident reduction programs in eastern German states were primarily focused on restrictive traffic regulation. Within two years after the opening, availability of high-powered vehicles and a 54% increase in motorized traffic led to a doubling of annual traffic deaths, despite "interim arrangements [which] involved the continuation of the speed limit of 100 km/h (62 mph) on autobahns and of 80 km/h (50 mph) outside cities. An extensive program of the four Es (enforcement, education, engineering, and emergency response
Emergency medical services
Emergency medical services are a type of emergency service dedicated to providing out-of-hospital acute medical care and/or transport to definitive care, to patients with illnesses and injuries which the patient, or the medical practitioner, believes constitutes a medical emergency...

) brought the number of traffic deaths back to pre-unification levels after ten years while traffic regulations were raised to western standards (e.g., 130 km/h (81 mph) freeway advisory limit, 100 km/h (62 mph) on other rural roads, and 0.5 milligrams BAC)
.

Enforcement


Speed limit enforcement
Speed limit enforcement
Speed limit enforcement is the action taken by appropriately empowered authorities to check that road vehicles are complying with the speed limit in force on roads and highways. Methods used include roadside speed traps set up and operated by the police and automated roadside 'speed camera'...

 is the action taken by appropriately empowered authorities to check that road vehicles
Vehicle
A vehicle is a device that is designed or used to transport people or cargo. Most often vehicles are manufactured, such as bicycles, cars, motorcycles, trains, ships, boats, and aircraft....

 are complying with the speed limit. Methods used include roadside speed traps set up and operated by the police and automated roadside speed camera systems which may incorporate the use of an automatic number plate recognition
Automatic number plate recognition
Automatic number plate recognition is a mass surveillance method that uses optical character recognition on images to read the license plates on vehicles. They can use existing closed-circuit television or road-rule enforcement cameras, or ones specifically designed for the task...

 system.

Effectiveness

The Synthesis of Safety Research Related to Speed and Speed Limits report sponsored by the Federal Highway Administration
Federal Highway Administration
The Federal Highway Administration is a division of the United States Department of Transportation that specializes in highway transportation. The agency's major activities are grouped into two "programs," the Federal-aid Highway Program and the Federal Lands Highway Program...

 published in 1998 found that changing speed limits on low and moderate speed roads appeared to have no significant effect on traffic speed or the number of crashes, whilst on high-speed roads such as freeways, increased speed limits generally resulted in higher traffic speeds and more crashes. It is also stated that there is limited evidence to suggest that speed limits have a positive effect on a system wide basis.Federal Highway Administration (1998) p. 2 'In general, changing speed limits on low and moderate speed roads appears to have little or no effect on speed and thus little or no effect on crashes. This suggests that drivers travel at speeds they feel are reasonable and safe for the road and traffic regardless of the posted limit. However, on freeways and other high-speed roads, speed limit increases generally lead to higher speeds and crashes. The change in speed is roughly one-fourth the change in speed limit. Results from international studies suggest that for every 1 mi/h change in speed, injury accidents will change by 5 percent (3 percent for every 1km/h). However there is limited evidence that suggests the net effect of speed limits may be positive on a system wide basis.'

The speed limit is commonly set at or below the '85th percentile speed' (which is the speed at which 85% of the traffic is travelling) and in the USA is typically set 8 to 12 mph (3.6 to 5.4 ) below that speed.

A 2003 review of speed limits for British Columbia
British Columbia
British Columbia is the westernmost of Canada's provinces and is known for its natural beauty, as reflected in its Latin motto, Splendor sine occasu . Its name was chosen by Queen Victoria in 1858...

 (Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...

) identified a number of places where speed limits had been increased and decreased in various countries and the observed changes in speeding, fatalities, injuries and property damage which followed these changes:
Results from lowering speed limits.
Country Speed limit reduction Reported change
Australia 110 km/h to 100 km/h Injury crashes declined by 19%
Australia 5–20 km/h decreases No significant change
Denmark 60 km/h to 50 km/h Fatal crashes declined by 24%
Injury crashes declined by 9%
Germany 60 km/h to 50 km/h Crashes declined by 20%
Sweden 110 km/h to 90 km/h Speeds declined by 14 km/h
Fatal crashes declined by 21%
Switzerland 130 km/h to 120 km/h Speeds declined by 5 km/h
Fatal crashes declined by 12%
UK 100 km/h to 80 km/h Speeds declined by 4 km/h
Crashes declined by 14%
USA (22 states) 8–32 km/h decreases No significant changes
Results from increasing speed limits:
Country Speed limit increase Reported change
Australia 100 km/h to 110 km/h Injury crashes increased by 25%
Australia (Victoria) 5–20 km/h increases Crashes increased overall by 8%, 35% decline in zones raised from 60 km/h to 80 km/h
USA 89 km/h to 105 km/h Fatal crashes increased by 21%
USA 89 km/h to 105 km/h Fatal crashes increased by 22%
Speeding increased by 48%
USA (40 states) 89 km/h to 105 km/h Fatalities increased by 15%
Decrease or no effect in 12 States
USA (Iowa) 89 km/h to 105 km/h Fatal crashes increased by 36%
USA (Michigan) 89 km/h to 105 km/h Fatal and injury crashes increased significantly on rural freeways
USA (Michigan) Various No significant changes
USA (Ohio) 89 km/h to 105 km/h Injury and property damage increased but not fatal crashes.
USA (40 states) 89 km/h to 105 km/h Statewide fatality rates decreased 3-5% (Significant in 14 of 40 states)
USA (22 states) 8 km/h to 24 km/h increase No significant changes


By contrast to the above a survey of speeds on South Dakota
South Dakota
South Dakota is a state located in the Midwestern region of the United States. It is named after the Lakota and Dakota Sioux American Indian tribes. Once a part of Dakota Territory, South Dakota became a state on November 2, 1889. The state has an area of and an estimated population of just over...

 Interstate roads in 2008 showed that 47% of drivers were driving over the 75 mph (120 km/h) speed limit, which is below observed 85th percentile speeds of 79-81 mph".

The Synthesis of Safety Research Related to Speed and Speed Limits report sponsored by the Federal Highway Administration published in 1998 found that increasing speed limits on freeways and high-speed roads increased speed and crashes.Federal Highway Administration (1998) p. 2 'In general, changing speed limits on low and moderate speed roads appears to have little or no effect on speed and thus little or no effect on crashes. This suggests that drivers travel at speeds they feel are reasonable and safe for the road and traffic regardless of the posted limit. However, on freeways and other high-speed roads, speed limit increases generally lead to higher speeds and crashes. The change in speed is roughly one-fourth the change in speed limit. Results from international studies suggest that for every 1 mi/h change in speed, injury accidents will change by 5 percent (3 percent for every 1km/h).'

Research in 1998 showed that the reduction of some 30 mph (13.4 m/s) United Kingdom speed limits to 20 mph (8.9 m/s) had achieved only a 1 mph drop in speeds and no discernible reduction in accidents; '20 mph speed limit zones' which use self enforcing traffic calming
Traffic calming
Traffic calming is intended to slow or reduce motor-vehicle traffic in order to improve the living conditions for residents as well as to improve safety for pedestrians and cyclists. Urban planners and traffic engineers have many strategies for traffic calming...

 achieved average speed reductions of 10 mph, child pedestrian accidents were reduced by 70% and child cyclist accidents by 48%.

Zones where speeds are set at 30 kph
30 kph zone
The 30 kph Zone, or 20 mph Zone, is a form of urban intervention where an area is designated with a 30 kilometer per hour limit, or 20 mile per hour limit. Note that 30 kph equals 19 mph, but 20 mph is more commonly used...

 (or 20 mph
30 kph zone
The 30 kph Zone, or 20 mph Zone, is a form of urban intervention where an area is designated with a 30 kilometer per hour limit, or 20 mile per hour limit. Note that 30 kph equals 19 mph, but 20 mph is more commonly used...

) are gaining popularity as they are found to be effective at reducing crashes and increasing community cohesion.

Studies undertaken in conjunction with Australia's move from 60 km/h (37.3 mph) speed limits to 50 km/h (31.1 mph) in built-up areas and found that the measure was effective in reducing both speed and the frequency and severity of crashes.

A study of the impact of the replacement of 60 km/h (37.3 mph) with 50 km/h (31.1 mph) speed limits in New South Wales
New South Wales
New South Wales is a state of :Australia, located in the east of the country. It is bordered by Queensland, Victoria and South Australia to the north, south and west respectively. To the east, the state is bordered by the Tasman Sea, which forms part of the Pacific Ocean. New South Wales...

, Australia showed only a 0.5 km/h drop in urban areas and a 0.7 km/h drop in rural areas. The report noted that widespread community compliance would require a combination of strategies including traffic calming treatments.

Information campaigns are also used by authorities to support speed limits, for example the Speeding. No one thinks big of you.
Speeding. No one thinks big of you.
Speeding. No one thinks big of you. is a multimedia advertising campaign launched in June 2007 in New South Wales, Australia, to convince young drivers that speeding and irresponsible driving is not 'cool'....

 campaign in Australia 2007.

Justification

Speed limits are set primarily to balance road traffic safety concerns with the effect on travel time and mobility. Speed limits are also sometimes used to reduce consumption of fuel or in response to environmental concerns.

Road traffic safety

According to a 2004 report from the World Health Organisation a total of 22% of all 'injury mortality' worldwide were from road traffic injuries in 2002World Heath Organisation (2004) p. 34 fig 2.1 and without 'increased efforts and new initiatives' casualty rates would increase by 65% between 2000 and 2020.World Heath Organisation (2004) p. 3 The report identified that the speed of vehicles was 'at the core of the problemWorld Heath Organisation (2004) p. 76 and said that speed limits should be set appropriately for the road function and design along with physical measures related to the road and the vehicle and effective enforcement by the police.World Heath Organisation (2004) p. 127 Road incidents are said to be the leading cause of deaths among children
Child mortality
Child mortality, also known as under-5 mortality, refers to the death of infants and children under the age of five. In 2010, 7.6 million children under five died , down from 8.1 million in 2009, 8.8 million in 2008, and 12.4 million in 1990. About half of child deaths occur in Africa....

 10 – 19 years of age (260,000 children die a year, 10 million are injured). They are also occasionally set to reduce vehicle emissions or fuel use.

Maximum speed limits place an upper limit on speed choice and if obeyed can reduce the differences in vehicle speeds by drivers using the same road at the same time. Traffic engineers observe that the likelihood of a crash happening is significantly higher if vehicles are traveling at speeds faster or slower than the mean
Mean
In statistics, mean has two related meanings:* the arithmetic mean .* the expected value of a random variable, which is also called the population mean....

 speed of traffic; when severity is taken into account the risk is lowest for those traveling at or below the median
Median
In probability theory and statistics, a median is described as the numerical value separating the higher half of a sample, a population, or a probability distribution, from the lower half. The median of a finite list of numbers can be found by arranging all the observations from lowest value to...

 speed and "increases exponentially for motorists driving faster".Federal Highway Administration (1998) page 2 'When the consequences of crashes are taken into account, the risk of being involved in an injury crash is lowest for vehicles that travel near the median speed or slower and increases exponentially for motorists traveling much faster'

It is desirable to attempt to reduce the speed of road vehicles in some circumstances because the kinetic energy
Kinetic energy
The kinetic energy of an object is the energy which it possesses due to its motion.It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity. Having gained this energy during its acceleration, the body maintains this kinetic energy unless its speed changes...

 involved in a motor vehicle collision is proportional to the square of the speed at impact
Collision
A collision is an isolated event which two or more moving bodies exert forces on each other for a relatively short time.Although the most common colloquial use of the word "collision" refers to accidents in which two or more objects collide, the scientific use of the word "collision" implies...

. The probability of a fatality is, for typical collision speeds, empirically correlated to the fourth power of the speed difference (depending on the type of collision, not necessarily the same as travel speed) at impact, rising much faster than kinetic energy.

The 2009 technical report An Analysis of Speeding-Related Crashes:Definitions and the Effects of Road Environments by the National Highway Traffic Safety Administration
National Highway Traffic Safety Administration
The National Highway Traffic Safety Administration is an agency of the Executive Branch of the U.S. government, part of the Department of Transportation...

 showed that ca 55 percent of all speeding-related crashes in fatal crashes were due to “exceeding posted speed limits” and 45 percent were due to “driving too fast for conditions”.

The speed limit will also take note of the speed at which the road was designed to be driven (the design speed
Design speed
The design speed is a tool used to determine geometric features of a new road during road design. The design speed chosen for a highway is a major factor in choosing superelevation rates and radii of curves, sight distance, and the lengths of crest and sag vertical curves...

) which is defined in the USA as "a selected speed used to determine the various geometric design features of the roadway". However traffic engineers recognize that "operating speeds and even posted speed limits can be higher than design speeds without necessarily compromising safety".
Vision Zero
Vision Zero
Vision Zero is a road traffic safety project started in Sweden in 1997 which aims to achieve a highway system with no fatalities or serious injuries in road traffic...

, which envision reducing road fatalities and serious injuries to zero by 2020, suggests the following "possible long term maximum travel speeds related to the infrastructure, given best practice in vehicle design and 100% restraint use":
Possible Maximum Travel Speeds
Type of infrastructure and traffic Possible travel speed (km/h)
Locations with possible conflicts between pedestrians and cars 30 km/h (19 mph)
Intersections with possible side impacts between cars 50 km/h (31 mph)
Roads with possible frontal impacts between cars, including rural roads 70 km/h (43 mph)
Roads with no possibility of a side impact or frontal impact (only impact with the infrastructure) 100 km/h (62 mph)+


"Roads with no possibility of a side impact or frontal impact" are sometimes designated as Type 1 ( motorways/freeways/Autobahns ), Type 2 ("2+2 road
2+2 road
A 2+2 road is a specific type of dual-carriageway being built in Ireland and Sweden, consisting of two lanes in each direction separated with a steel cable barrier. They do not have hard shoulders. Junctions are at-grade roundabouts and minor roads cross under or over the mainline without...

s") or Type 3 ("2+1 road
2+1 road
2+1 road is a specific category of three-lane road, consisting of two lanes in one direction and one lane in the other, alternating every few kilometres, and separated usually with a steel cable barrier. Traditional roads of at least width can be converted to 2+1 roads and reach near-motorway...

s"). These roadways have crash barriers
Traffic barrier
Traffic barriers keep vehicles within their roadway and prevent vehicles from colliding with dangerous obstacles. Traffic barriers installed at the road side also prevent errant vehicles from traversing steep slopes. Traffic barriers installed at the medians of divided highways are also referred...

 separating opposing traffic, limited access, grade separation
Grade separation
Grade separation is the method of aligning a junction of two or more transport axes at different heights so that they will not disrupt the traffic flow on other transit routes when they cross each other. The composition of such transport axes does not have to be uniform; it can consist of a...

 and prohibitions on slower and more vulnerable road users. Undivided rural roads can be quite dangerous even with speed limits that appear low by comparison. For example, in 2008, Germany's 100 km/h (62 mph)-limited rural roads had a fatality rate of 9.5 deaths per billion travel-km, over four times higher than the autobahn rate of 2.2 deaths. Autobahns accounted for 33% of German road travel in 2008, but just 11% (495 of 4,477) of traffic deaths.

Fuel efficiency

Fuel efficiency sometimes affects speed limit selection. The United States instituted a National Maximum Speed Law
National Maximum Speed Law
The National Maximum Speed Law in the United States was a provision of the 1974 Emergency Highway Energy Conservation Act that prohibited speed limits higher than . It was drafted in response to oil price spikes and supply disruptions during the 1973 oil crisis...

 of 55 mph (89 km/h) as part of the Emergency Highway Energy Conservation Act in response to the 1973 oil crisis
1973 oil crisis
The 1973 oil crisis started in October 1973, when the members of Organization of Arab Petroleum Exporting Countries or the OAPEC proclaimed an oil embargo. This was "in response to the U.S. decision to re-supply the Israeli military" during the Yom Kippur war. It lasted until March 1974. With the...

 to reduce fuel consumption. According to a report published in 1986 by The Heritage Foundation
The Heritage Foundation
The Heritage Foundation is a conservative American think tank based in Washington, D.C. Heritage's stated mission is to "formulate and promote conservative public policies based on the principles of free enterprise, limited government, individual freedom, traditional American values, and a strong...

, a Conservative advocacy group, the law was widely disregarded by motorists and hardly reduced consumption at all. In 2009 The American Trucking Associations
American Trucking Associations
The American Trucking Associations , founded in 1933, is the largest national trade association for the trucking industry. Through a federation of other trucking groups, industry-related conferences, and its 50 affiliated state trucking associations, ATA represents more than 37,000 members covering...

 called for a 65 mph speed limit and also national fuel economy standards claiming that the lower speed limit was not effective at saving fuel.

Environmental considerations

Speed limits can also be used to improve local air quality issues or other factors affecting environmental quality
Environmental quality
Environmental quality is a set of properties and characteristics of the environment, either generalized or local, as they impinge on human beings and other organisms...


for example the "environmental speed limits" in the United States including one in an area of Texas
Texas
Texas is the second largest U.S. state by both area and population, and the largest state by area in the contiguous United States.The name, based on the Caddo word "Tejas" meaning "friends" or "allies", was applied by the Spanish to the Caddo themselves and to the region of their settlement in...

.

The European Union
European Union
The European Union is an economic and political union of 27 independent member states which are located primarily in Europe. The EU traces its origins from the European Coal and Steel Community and the European Economic Community , formed by six countries in 1958...

 is also increasingly using Speed Limits as in response to environmental concerns.

Advocacy

Speed limits, and especially some of the methods used to attempt to enforce them, have always been controversial. There are a variety of notable organisations and individuals who, for a variety of often passionately held views, oppose or support the use of speed limits or the way they are enforced.

Opposition

Speed limits, and their enforcement have been opposed by various groups and for various reasons since their inception. Historically, the AA
The Automobile Association
The Automobile Association , a British motoring association founded in 1905 was demutualised in 1999 to become a private limited company which currently provides car insurance, driving lessons, breakdown cover, loans and motoring advice, and other services...

 was formed in 1905, initially to warn members about speed trap
Speed Trap
Speed Trap is a live jazz album by Peter King, recorded at Ronnie Scott's Jazz Club in September 1994, and released in 1996 under the Ronnie Scotts Jazz House label...

s.

In more recent times some advocacy groups seek to have certain speed limits as well as other measures removed. For example, automated camera enforcement has been criticised by motoring advocacy groups the Association of British Drivers
Association of British Drivers
The Association of British Drivers , founded in 1992, is a British motorists' advocacy group."The Association of British Drivers" is the sole operating name of "Pro-Motor", a company limited by guarantee and registered in the United Kingdom....

, the North American National Motorists Association
National Motorists Association
The National Motorists Association is a grassroots organization whose revenue is membership- and donation-driven. It was created in 1982 to "to represent and protect the interests of North American motorists", and advocates a "Motorist Bill of Rights".-History:The NMA, originally called the...

, and the German Auto Club
ADAC
The ADAC is Germany's and Europe's largest automobile club, with more than 17 million members in June 2010. It was founded on May 24, 1903 as "Deutsche Motorradfahrer-Vereinigung" and was renamed in 1911...

.

Arguments used by those advocating a relaxation of speed limits or their removal include:
  • A 1994 peer-reviewed paper by Charles A. Lave et al. titled Did the 65 mph Speed Limit Save Lives? stated that evidence that a higher speed limit may be positive on a system wide in the United States by shifting more traffic to these safer roads.
  • A 1998 report in the Wall Street Journal title 'Highways are safe at any speed' stated that when speed limits are set artificially low, tailgating, weaving and speed variance (the problem of some cars traveling significantly faster than others) make roads less safe.
  • In 2010 German Auto Club
    ADAC
    The ADAC is Germany's and Europe's largest automobile club, with more than 17 million members in June 2010. It was founded on May 24, 1903 as "Deutsche Motorradfahrer-Vereinigung" and was renamed in 1911...

     (a major motoring organisation) concluded an autobahn speed limit was unnecessary because numerous countries with a general highway speed limit had worse safety records than Germany, for example Denmark, Belgium, Austria, and the United States.
  • In 2008, the German Automobile Manufacturer's Association
    Verband der Automobilindustrie
    The Verband der Automobilindustrie e. V., short VDA, is a German interest group of the German automobile industry, both automobile manufactures and automobile component suppliers. The group is located in Berlin, Germany...

     called general limits "patronizing", arguing instead for variable speed limits. The Association also noted that "raising the speed limits in Denmark (in 2004 from 110 km/h to 130 km/h) and Italy (2003 increase on on six-lane highways from 130 km/h to 150 km/h) had no negative impact on traffic safety. The number of accidental deaths even declined" .
  • Safe Speed
    Safe Speed
    Safe Speed is a United Kingdom based pressure group. While notionally supporting road safety the organisation primarily campaigns against speed cameras...

    , a UK advocacy organisation campaigns for higher speed limits and to scrap speed cameras on the basis that the benefits were exaggerated and that they may actually increase casualty levels; their ePetition to the UK government in 2007 calling for speed cameras to be scrapped received over 25,000 signatures.

Support

Various other advocacy groups press for stricter limits and better enforcement. Historically, the Pedestrians' Association and the Automobile Association were described as "bitterly opposed" in the early years of United Kingdom motoring legislation. The Pedestrians Association was formed in the United Kingdom
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...

 in 1929 to protect the interests of the pedestrian. Their president published a critique of motoring legislation and the influence of motoring groups in 1947 title 'Murder most foul' which laid out in an emotional but detailed way the situation as they saw it and called for tighter speed limits. More recently RoadPeace
RoadPeace
RoadPeace is the national charity for road crash victims in the UK. It supports the people affected by road crashes with emotional and practical support and advocacy. It operates a help line and provides practical support to people affected...

 was founded in 1991 with an aim to stop road victims being "treated by the economy as acceptable, by the judicial system as trivial and by society as accidents" and called for a default 20 mph speed limit in residential areas.

Vision Zero is "a philosophy of road safety that eventually no one will be killed or seriously injured within the road transport system." http://www.monash.edu.au/muarc/reports/papers/visionzero.html

See also

  • Rail speed limits in the United States
  • Speed limits by country
    Speed limits by country
    A road speed limit is the limit of speed allowed by law for road vehicles, either maximum limit or minimum limit. Speed limits are commonly set by the legislative bodies of national or local governments.-Overview:...

  • Traffic violations reciprocity
    Traffic Violations Reciprocity
    Under traffic violations reciprocity agreements, non-resident drivers are treated like residents when they are stopped for a traffic offense that occurs in another jurisdiction. They also ensure that punishments such as "points" on one's license and the ensuring increase in insurance premiums...


Further reading


External links

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