A typical 60 km/h speed limit sign used in Australia

A typical speed limit sign in the United States showing a 50 mph restriction.

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,^[1][2] although this was reduced to 140 km/h (87 mph) in 2011.^[3][4] 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.^[5][6][7] Rural areas on the Isle of Man,^[8] the Indian states of Andhra Pradesh^[9] and Maharashtra^[10] 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.)^{[n 1]} 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. ^[11]

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 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.

History[link]

Antique New Hampshire speed limit sign.

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 of 10 mph (16 km/h) which was then reduced to 4 mph (6 km/h) in rural areas, 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, Kent, who on 28 January 1896 was fined for speeding at 8 mph (13 km/h). He was fined 1 shilling plus costs.^[12][13][14] Passage of the Locomotives on Highways Act 1896, 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.

Regulations[link]

Speed limit sign in Germany, showing a 60 km/h restriction. Signs in other European countries are similar but have a different font and size.

Speed limits on European Motorways in km/h.

All^{[citation needed]} countries use metric units (kilometres per hour), except for the United States and the United Kingdom, where speed limits are given in miles per hour.

Basic rule: reasonable speed[link]

Drivers are required to drive at a safe speed for conditions. In the United States this requirement is referred to as the basic rule,^[15] but more generally in Britain and elsewhere in common law as the reasonable man requirement.^[16] 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.^[17] 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".^[18]

Maximum speed limits[link]

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, large signposts showing the national (default) speed limits of the respective country are usually erected immediately after border crossings, with a repeater sign some 200 to 500 m (660 to 1,600 ft) 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 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 provides guidelines for the appearance of speed limit signs. In California, freeway speed limits are often labeled "MAXIMUM SPEED" instead. In Oregon, many speed limit signs just say "SPEED" and the number. 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. Australian signs are rectangular but have a red circle like the conventional signs.^[19]

Posted maximum speeds are normally based on ideal driving conditions.^{[citation needed]}

Minimum speed limits[link]

Some roads also have "minimum speed limits", where slow speeds can impede traffic flow or be dangerous^[20] and on motorways slower vehicles such as horse drawn vehicles, bicycles and mopeds can be banned, e.g. in the United Kingdom.^[21]

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[link]

Example variable speed limit sign in the United States.

In 1965, the first known experiments with variable speed limit signs took place on a 30 km stretch of German motorway A8 between Munich and the border city of Salzburg, Austria. 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.^[22] Beginning in the 1970s, additional 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, 1,300 km (810 mi) of German motorways were equipped with such systems.^[23]

In the late 1960s, heavily-traveled portions of the New Jersey Turnpike 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.^[24] More typically, variable speed limits are used on remote stretches of highway in the United States in areas with extreme changes in driving conditions.[1] For example, variable limits were introduced in Oct 2010 on a 52-mile stretch of Interstate 80 in Wyoming, replacing the winter season speed reduction from 75 to 65-mph that had been in place since 2008.^[25][26] Similarly, Interstate 90 at Snoqualmie Pass and other mountain passes in Washington State variable speed limits are used to slow traffic in severe winter weather.[2] ^[27] 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.^[28]

A variable speed limit was introduced on part of Britain's M25 motorway in 1995 (on the busiest 14-mile (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.^[29] 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 will have the facility for variable speed limits.^[30] In January 2010 temporary variable speed cameras on the M1 between J25 and J28 were made permanent.^[31]

New Zealand introduced variable speed limits in February 2001. The first installation was on the Ngauranga Gorge 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.^[32]

In 2006, Austria 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) to 160 kilometres per hour (99 mph).^[33] Then Austrian Transport Minister Hubert Gorbach called the experiment "a milestone in European transport policy-despite all predictions to the contrary"; however, the experiment was discontinued.

Roads without speed limits[link]

German border crossing sign showing 50 km/h (31 mph) limit in built-up areas, 100 km/h (62 mph) in rural areas, but only an advisory 130 km/h (81 mph) limit for the Autobahn

Many roads without a maximum limit became permanently limited following the 1973 oil crisis. For example, Switzerland 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.^[34]

Montana and Nevada 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 of 1974.^[35] 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 requirement of the Montana Constitution,^[36] Montana's legislature imposed a 75 mph (121 km/h) limit on rural freeways in 1999, although the same wording in the basic rule remains.

Australia's Northern Territory 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.^[37] The per-capita fatality rate in 2006 was the highest in the OECD and twice the Australian average.^[38] 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 than normally published, these statistics showed a reduction in fatalities along the highways where 130 km/h limits were introduced.^[39][40][41]. The opposition continues to argue for a return to "open speed limits". ^[42][43]

The Isle of Man 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 for safety reasons were not progressed following consultation. ^[8] Measured travel speeds on the island are relatively low.^[44]

As of 2008, 52% of the German autobahns have only advisory limits (Richtgeschwindigkeit), 15% have temporary speed limits due to weather or traffic conditions and 33% have permanent speed limits.^[45] The length of speed-unrestricted autobahns slowly expanded after the opening of the East German borders in November 1989. Prior to German reunification 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) 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) .^[46]

Enforcement[link]

Gatso speed camera

Speed limit enforcement is the action taken by appropriately empowered authorities to check that road vehicles 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 system.

Effectiveness[link]

The Synthesis of Safety Research Related to Speed and Speed Limits report sponsored by the Federal Highway Administration 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.^{[n 2]}

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)^[47] and in the USA is typically set 8 to 12 mph (13 to 19 km/h) below that speed.^[48]

A 2003 review of speed limits for British Columbia (Canada) identified a number of studies into the effects of reductions in speed limits and the observed changes in speeding, fatalities, injuries and property damage which followed:^{[n 3]}

By contrast to the above a survey of speeds on South Dakota 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".^[50]

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.^{[n 4]}

Research in 1998 showed that the reduction of some 30 mph (48 km/h) United Kingdom speed limits to 20 mph (32 km/h) 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 achieved average speed reductions of 10 mph, child pedestrian accidents were reduced by 70% and child cyclist accidents by 48%.^[51]

Zones where speeds are set at 30 kph (or 20 mph) are gaining popularity ^[52] as they are found to be effective at reducing crashes and increasing community cohesion. ^[53]

Studies undertaken in conjunction with Australia's move from 60 km/h (37 mph) speed limits to 50 km/h (31 mph) in built-up areas and found that the measure was effective in reducing both speed and the frequency and severity of crashes.^[54]

A study of the impact of the replacement of 60 km/h (37 mph) with 50 km/h (31 mph) speed limits in 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.^[55]

Information campaigns are also used by authorities to support speed limits, for example the Speeding. No one thinks big of you. campaign in Australia 2007.

Justification[link]

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.^[56]

Road traffic safety[link]

The Pan-American Highway with central median and no freestanding obstructions increasing level of safety at high speed

Traffic calming can be effective on lower speed roads

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 2002^{[n 5]} and without 'increased efforts and new initiatives' casualty rates would increase by 65% between 2000 and 2020.^{[n 6]} The report identified that the speed of vehicles was 'at the core of the problem^{[n 7]} 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.^{[n 8]} Road incidents are said to be the leading cause of deaths among children 10 – 19 years of age (260,000 children die a year, 10 million are injured).^[57] 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.^{[n 9]} 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 speed of traffic;^{[n 10]} when severity is taken into account the risk is lowest for those traveling at or below the median speed and "increases exponentially for motorists driving faster".^{[n 11]}

It is desirable to attempt to reduce the speed of road vehicles in some circumstances because the kinetic energy involved in a motor vehicle collision is proportional to the square of the speed at impact. 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,^[58] 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 showed that about 55 percent of all speeding-related crashes in fatal crashes had "exceeding posted speed limits" among their crash factors, and 45 percent had "driving too fast for conditions" among their crash factors. However, the authors of the report did not attempt to determine whether the factors were actually a crash cause, contributor, or an unrelated factor.^[59] Furthermore, separate research finds that only 1.6% of crashes are "caused" by drivers what exceed the posted speed limit.^[60] Finally, exceeding the posted limit may not be a remarkable factor in crash analysis as there exist roadways where virtually all motorists are in technical violation of the law.^[61]

The speed limit will also take note of the speed at which the road was designed to be driven (the design speed) which is defined in the USA as "a selected speed used to determine the various geometric design features of the roadway".^[62] However traffic engineers recognize that "operating speeds and even posted speed limits can be higher than design speeds without necessarily compromising safety". ^[63]

Vision Zero, 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":^[64]

"Roads with no possibility of a side impact or frontal impact" are sometimes designated as Type 1 ( motorways/freeways/Autobahns ), Type 2 ("2+2 roads") or Type 3 ("2+1 roads").^[66] These roadways have crash barriers separating opposing traffic, limited access, grade separation 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.^[67] Autobahns accounted for 33% of German road travel in 2008,^[68] but just 11% (495 of 4,477) of traffic deaths.

Fuel efficiency[link]

Fuel efficiency sometimes affects speed limit selection. 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.^[69] 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.^[70] In 2009 The American Trucking Associations 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.^[71]

Environmental considerations[link]

Speed limits can also be used to improve local air quality issues or other factors affecting environmental quality^[72] for example the "environmental speed limits" in the United States including one in an area of Texas.^[73]

The European Union is also increasingly using Speed Limits as in response to environmental concerns.^[56]

Advocacy[link]

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[link]

Speed limits, and their enforcement have been opposed by various groups and for various reasons since their inception. Historically, the AA was formed in 1905, initially to warn members about speed traps.^[74]

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,^[75][76] the North American National Motorists Association,^[77][78] and the German Auto Club.^[79]

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.^[80]
• 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.^[81]
• In 2010 German Auto Club (a major motoring organisation) argued that 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.^[79]
• In 2008, the German Automobile Manufacturer's Association called general limits "patronizing"^[82], arguing instead for variable speed limits. The Association also stated that "raising the speed limits in Denmark (in 2004 from 110 km/h to 130 km/h) and Italy (2003 increase 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" ^[83].
• Safe Speed, a UK advocacy organisation campaigns for higher speed limits^[84] and to scrap speed cameras on the basis that the benefits were exaggerated and that they may actually increase casualty levels;^[85] their ePetition to the UK government in 2007 calling for speed cameras to be scrapped received over 25,000 signatures.^[86]

Support[link]

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.^[87] The Pedestrians Association was formed in the United Kingdom 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.^[88] More recently RoadPeace 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.^[89]

Vision Zero is "a philosophy of road safety that eventually no one will be killed or seriously injured within the road transport system." [3]

See also[link]

• Rail speed limits in the United States
• Speed limits by country
• Traffic violations reciprocity

Notes[link]

References[link]

Documents referenced from 'Notes' section

Other references for article

Further reading[link]

• Actual Speeds on the Roads Compared to the Posted Limits, Final Report 551, Arizona Dept of Transportation, October 2004.
• Effects of Raising and Lowering Speed Limits on Selected Roadway Sections, United States Publication No. FHWA-RD-97-084, January 1997.
• Effect of 20 mph traffic speed zones on road injuries in London, 1986-2006: controlled interrupted time series analysis British Medical Journal 2009.
• Special Report 254: Managing Speed, Transportation Research Board, 1998.
• Speed: Understanding Design, Operating, and Posted Speed Texas Transportation Institute, College Station, TX. Research Report 1465-1. March 1996. R.A. Krammes, K. Fitzpatrick, J.D. Blaschke, D.B. Fambro.
• The Speeding Driver: Who, How and Why? A research report by the Scottish government into the psychology of the speeding driver.
• Transport, Local Government and the Regions - Ninth Report A comprehensive UK report into the effects of speeding.

External links[link]

Wikimedia Commons has media related to: Speed limit signs

• A Walk Through The History of Speed Limit Signs in The US
• John F. Carr's State Traffic and Speed Laws