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Speed limit enforcement is the effort made by appropriately empowered authorities to improve driver compliance with speed limits. 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. Traditionally, police officers used stopwatches to measure the time taken for a vehicle to cover a known distance. More recently, radar guns and automated in-vehicle systems have come into use.
A worldwide review of studies found that speed cameras led to a reduction of "11% to 44% for fatal and serious injury crashes". The UK Department for Transport estimated that cameras had led to a 22% reduction in personal injury collisions and 42% fewer people being killed or seriously injured at camera sites. The British Medical Journal recently reported that speed cameras were effective at reducing accidents and injuries in their vicinity and recommended wider deployment. An LSE study in 2017 found that "adding another 1,000 cameras to British roads could save up to 190 lives annually, reduce up to 1,130 collisions and mitigate 330 serious injuries."
The perception that speed limits in a given location are being set and enforced primarily to collect revenue rather than improve traffic safety has led to controversy.
Traffic calming was built into the 1865 Locomotive Act in the UK, which set a speed limit of 2 miles per hour (3.2 km/h) in towns and 4 miles per hour (6.4 km/h) out of town, by requiring a man with a red flag to walk 60 yards (55 m) ahead of qualifying powered vehicles. The distance ahead of the pedestrian crew member was reduced to 20 yards (18 m) in 1878 and the vehicles were required to stop on the sight of a horse. The speed limit was effectively redundant as vehicle speeds could not exceed the speed at which a person could walk.
By 1895 some drivers of early lightweight steam-powered autocars assumed that these would be legally classed as a horseless carriage and would therefore be exempt from the need for a preceding pedestrian. A test case was brought by motoring pioneer John Henry Knight, who was subsequently convicted with using a locomotive without a licence. The Locomotives on Highways Act 1896 lifted some of the restrictions introduced by the 1865 Act, notably raising the speed limit for "light locomotives" under 3 tonnes to 14 miles per hour (23 km/h). The speed limit was lifted again by the Motor Car Act 1903 to 20 miles per hour (32 km/h).
A Royal Commission on motorcars in the UK reported in 1907 and raised concerns about the manner in which speed traps were being used to raise revenue in rural areas rather than being used to protect lives in towns. In parliamentary debates at the time it was observed that "Policemen are not stationed in the villages where there are people about who might be in danger, but are hidden in hedges or ditches by the side of the most open roads in the country" and were "manifestly absurd as a protection to the public, and they are used in many counties merely as a means of extracting money from the passing traveller in a way which reminds one of the highwaymen of the Middle Ages".
In 1905 The Automobile Association was formed to help motorists avoid police speed traps. Chief Justice, Lord Alverston brought a test court case in 1910 ('Betts -v- Stevens') against an Automobile Association patrolman and a potentially speeding motorist—the judge ruled that where a patrolman signals to a speeding driver to slow down and thereby avoid a speed trap, that person would have committed the offence of "obstructing an officer in the course of his duty" under the Prevention of Crimes Amendment Act 1885. Subsequently, the organisation developed a coded warning system which was used until the 1960s whereby a patrolman would always salute the driver of a passing car that displayed a visible AA badge unless there was a speed trap nearby, on the understanding that their officers could not be prosecuted for failing to salute.
Gatsometer BV, founded in 1958 by rally driver Maurice Gatsonides, produced the 'Gatsometer' which was described as "a revolutionary speed-measuring device". Developed initially for improving his race times, it was later marketed as police speed enforcement tool. Gatsometer claim to have developed the first radar for use with road traffic in 1971, but this claim is undermined by evidence that radar detectors were already for sale in 1967. Gatsometer BV produced the world's first mobile speed traffic camera in 1982.
Speed limits were originally enforced by manually timing or "clocking" vehicles travelling through "speed traps" defined between two fixed landmarks along a roadway that were a known distance apart; the vehicle's average speed was then determined by dividing the distance travelled by the time taken to travel it. Setting up a speed trap that could provide legally satisfactory evidence was usually time consuming and error prone, as it relied on its human operators.
VASCAR is a device that semi-automates the timing and average speed calculation of the original manually operated "speed trap". An observer on the ground, in a vehicle or in the air simply presses a button as a vehicle passes two landmarks that are a known distance apart, typically several hundred metres.
Automatic number plate recognition (ANPR) systems that use a form of optical character recognition read the vehicle's licence or registration plate. A computer system reads vehicle registration plates at two or more fixed points along a road, usually hundreds of meters or even kilometers apart, then uses the known distance between them to calculate a vehicle's average speed. From the mean value theorem, we know that the vehicle's speed must equal its average speed at some time between the measurements. If the average speed exceeds the speed limit, then a penalty is automatically issued.
Speed enforcement using average speed measurement is expressly prohibited in California.
Instantaneous speed cameras measure the speed at a single point. These may either be a semi-permanent fixture or be established on a temporary basis. A variety of technologies can be used:
Officers in some jurisdictions may also use pacing, particularly where a more convenient radar speed measuring device is not available—a police vehicle's speed is matched to that of a target vehicle, and the calibrated speedometer of the patrol car used to infer the other vehicle's speed.
In recent years many jurisdictions began using cameras to record violators. These devices detect vehicles that are exceeding the speed limit and take photos of these vehicles' license plates. A ticket is then mailed out to the registered owner.
Some jurisdictions such as Australia and Ohio, allow prosecutions based on a subjective speed assessment by a police officer. In the future there is the potential to track speed limit compliance via GPS black boxes for recidivist speeders identified in the Australian National Road Safety Strategy 2011 - 2020 section on Intelligent speed adaptation.
While digital cameras can be used as the primary means of speed detection when combined with automatic number plate recognition (ANPR) average-speed camera systems, their use is more commonly restricted to evidence gathering where speeding offences are detected by various other types of sensors such as Doppler radar, piezo strips, infrared or laser devices.
Photographs are typically time-stamped by a high resolution timing device so that a vehicle's speed can be checked manually after the fact if necessary using the secondary method of calculating its speed between a series of calibrated lines (known as "Dragon's Teeth") painted on the road surface.
The change from analogue "wet film" to digital technology has revolutionised speed cameras, particularly their maintenance and the back-office processing required to issue penalty notices. Images from digital cameras can be uploaded in seconds to a remote office over a network link, while optical character recognition software can automate the "reading" of vehicle registration numbers.
Some drivers use passive radar detectors or LIDAR detectors to detect police radar or LIDAR signals, with the intention of avoiding or evading prosecution by slowing down before entering an enforcement zone. The legal standing of these type of devices varies by jurisdiction. For example, they are legal in most of the United States, but not in most of Canada. Active devices might also be used—in this instance, radar or LIDAR signals are typically jammed with counter emissions. These devices are more frequently illegal than passive devices.
Drivers may flash their lights to approaching drivers to warn them of a speed trap. The legal standing of this action also varies by jurisdiction. In the United States, it is common for motorists with Citizen's Band (CB) radios to report the location of speed traps over the CB radio to other motorists.
In 2006, the UK Automobile Association controversially published a road map that included the location for thousands of speed cameras—the first time such information was available in printed form, although more accurate and frequently updated GPS-based information was freely available for some time before that.
Mobile applications such as Njection, Trapster, and Waze provide mobile information to drivers on speed traps and traffic conditions. These applications rely on users to keep the databases current. In addition to mobile applications that might be considered evasion-centric, there are other similar mobile applications that are classified as Intelligent speed adaptation technologies that are considered too compliance centric and in Australia both National and State Road Safety Strategies encourage the adoption of such technologies.
Groups such as the National Motorists Association define speed trap more narrowly as a place where "traffic enforcement is focused on extracting revenue from drivers instead of improving safety". When highway speed limits drop suddenly just as they enter a municipality which collects large amounts of revenue from traffic tickets, a safety hazard can be introduced, and efforts have been made in the U.S. to ban this practice. Some police forces have even been forced to disband as a result of overzealous enforcement. However, a meta-analysis of studies finds automated ticketing machines that enforce speed limits may have reduced the number of traffic injuries and deaths.
Kevin Richardson proposed the idea of rewarding drivers travelling at or below the posted limit with a cash lottery, funded by the fines on speeding drivers. This was demonstrated in Stockholm, Sweden, in November 2010.
Speed limits may not be enforced for speeds close to the legal limit. In the United States, speeding enforcement tolerance is usually up to the discretion of the arresting officer. Some states (such as Pennsylvania and Florida) have official tolerances.
A study of over 1000 drivers caught speeding in the U.S. and in Canada examined factors that predicted fines issued by police officers. In both countries, drivers were stopped for speeding on average 26 km/h (16 mph) over the speed limit and received fines of approximately $144 USD. As expected, drivers traveling at higher speeds over the limit received higher fines. What drivers said to the police also affected the amount of the fine. 46% percent of drivers in the study reported offering an excuse (e.g. "I didn't realize the speed I was driving"), which was the most common type of verbal response. Excuses, justifications, and denials did not reduce the amount of the fine. Almost 30% of drivers expressed remorse (e.g., "I'm sorry") and received a considerable reduction in fines. Offers of remorse were most effective at higher speeds over the limit. For example, American speeders who offered remorse for traveling at higher speeds over the limit (21 mph) received fines that were $49 USD lower than drivers speeding the same amount, but who did not say they were sorry. Although this research indicated that apologies can be related to lower fines for speeding most drivers who offered remorse did not get off without punishment, however. To maintain a relatively normal sample of speeders, a small percentage of drivers who reported extreme speeds (80 km/h (50 mph) or more over the limit) or very severe fines ($500 USD or more) were excluded.
As older vehicle construction regulations allowed a speedometer accuracy of +/- 10%, in the United Kingdom ACPO guidelines recommend a tolerance level of the speed limit "+10% +2 mph" (e.g., a maximum tolerance in a 30 mph (50 km/h) zone of 30 + (30 × 10% = 3) + 2 = 35 mph).
In Germany, at least a 3 km/h tolerance (3% of measured speed when speeding over 100 km/h) in favor of the offender is always deducted. This tolerance can increase up to 20% depending on the method of measurement. Fines for speeding depend on how high above the speed limit the measured speed is and where the offense occurred. Speeding in built-up areas invariably carries higher fines than outside city limits. While fines for minor offenses tend to be moderate, speeds in excess of 20 km/h (12 mph) above the limit in built-up areas result in distinctly higher fines and points on the driver's license, and depending on the speed at which the offender was clocked, may lead to a driving ban of at least one month.
The state of Victoria in Australia allows for only a 3 kilometres per hour (1.9 mph) tolerance for mobile speed cameras and 2 kilometres per hour (1.2 mph) for fixed cameras on the basis that although the increased risk is lower there are very many more drivers involved which creates a substantial risk across the road network. An alternative view is that police devices are accurate to 1 km/h, and that a 2–3 km/h tolerance is the minimum margin that police require to defeat any challenge in court regarding the accuracy of their speed measurement equipment. Speed tolerance in New South Wales was an election issue in 2011, following a move by the budget committee of the previous Labor state government to abolish the 3 km/h margin in order to increase revenue.
Speed limit policy can affect enforcement. According to a 1994 report by the AASHTO, "experience has shown that speed limits set arbitrarily below the reasonable and prudent speed perceived by the public are difficult to enforce, produce noncompliance, encourage disrespect for the law, create unnecessary antagonism toward law enforcement officers, and divert traffic to lesser routes".
In Mexico, the maximum speed limit is 80 kilometres per hour (50 mph) on urban freeways on other urban roads. However, fines are only given when speeding above 90 kilometres per hour (56 mph), thus giving a 10 kilometres per hour (6.2 mph) tolerance. The Mexican highway patrol (Mexico City) and traffic law enforcement officers (Guadalajara) may enforce speed laws only when a car is speeding above reasonable speeds in regard of the amount of traffic. Maximum speed for all Mexican highways is 110 kilometres per hour (68 mph). Speeding fines are given to those going 130 kilometres per hour (81 mph) and up to 220 kilometres per hour (140 mph). Police may however place a squad car as a pace car so drivers behind cannot exceed 100 kilometres per hour (62 mph); this is common during Summer and Winter holiday season.
Local conditions, law and police practices mean that the tactics adopted to catch speeding motorists vary considerably. In some regions, police may adopt a more subtle approach, concealing themselves and their equipment as much as possible; other jurisdictions require highly visible policing, with cameras painted yellow, and camera operators not permitted to use approaches such as attaching the camera to what may appear to be a broken-down vehicle when enforcing speed limits.
Authorities are not able to monitor every vehicle on every road—limited resources generally mean that enforcement needs to be targeted. A New Zealand study concluded that actual enforcement as well as the perceived chance of being caught both contributed to changes in drivers' behaviour.
Many jurisdictions operate traffic violations reciprocity where non-resident drivers are treated like residents when they are stopped for a traffic offense that occurs in another jurisdiction. They also ensure that penalties such as demerit points and the ensuing increase in insurance premiums follow the driver home. The general principle of such interstate, inter-provincial, and/or international compacts is to guarantee the rule 'one license, one record.'
In 2001, Acme-Rent-a-Car in Connecticut controversially tried to use a contractual clause in the rental agreement to issue speeding fines to any of its customers that exceeded speed limits as detected by GPS tracking units its cars. The company actions were challenged and defeated in court.
Doug Georgianni, 51, was shot as he operated a photo radar van on a Phoenix freeway and later died at a hospital.
In August 2005, in Sydney, Australia a speed camera photograph was challenged on the basis that an MD5 cryptographic hash function used to protect the digital photograph from tampering was not robust enough to guarantee that it had not been altered. Magistrate Lawrence Lawson demanded that the Roads and Traffic Authority (RTA) produce an expert witness who could prove the photographs were tamper-proof, but the RTA was unable to provide such evidence. The defendant was acquitted and awarded court costs.
In June 2011, the New South Wales (NSW) government was reported to have raised A$350 million over the previous five years from speed cameras. The Roads Minister accused the previous Labor government of using speed cameras to raise revenue; the Auditor-General was therefore tasked with investigating all 141 fixed speed cameras in use throughout the state. Following the release of the report, 38 speed cameras, located primarily on highways, were switched off after the Auditor-General determined that they had no significant road safety benefit. The report found the majority of fixed speed cameras had a proven road safety benefit. The report also concluded that it was "too early" to conclude if mobile speed cameras affected road safety, although early results indicated drivers might be speeding less. To address public concerns, the RTA would now monitor the effectiveness of individual fixed speed cameras annually.
It is predicted that the South Australia (SA) government will raise A$138 million in the 2011–12 year from speed limit enforcement activities. They raised A$114 million in 2010–11. The SA government are resisting moves by their opposition to commission an inquiry into whether speed cameras are being used effectively and efficiently: to improve road safety, to raise revenue, or both.
In 2004, in a Poltech fixed speed camera on Melbourne's Western Ring Road recorded a four-cylinder Datsun 120Y sedan travelling at 158 km/h, but testing found this vehicle only capable of 117 km/h. A Victorian state government inquiry found that maintenance and accuracy checks had not been done regularly.
Victoria achieved record low road tolls in both 2008 and 2009. Newspaper reports credited a co-ordinated and well-funded campaign that focused on higher risk young drivers, more aggressive policing, increased police activity, drink driving, and in 2009, a 50% increase in the use of mobile speed cameras.
After growing numbers of complaints about incorrect and inappropriate fines, Victoria's Auditor-General plans to investigate whether speed cameras are being used primarily to raise revenue for the state government rather than to improve road safety.
The Victoria government forecasts that a revenue of A$245 million will be raised from fines levied on drivers breaking Victorian road rules, a large proportion being from speed limit enforcement, in 2011.
Speed limit enforcement cameras were a substantial election issue in the provinces of Ontario and British Columbia, and were abolished by Premiers Mike Harris in 1995 and Gordon Campbell in 2001, however current Ontario premier Kathleen Wynne has announced plans to reinstate their use .
In February 2006, Edmonton, Alberta, erupted in scandal when it was alleged that two police officers accepted bribes from private contractors who received lucrative contracts to provide speed limit enforcement cameras. The officers and contractor involved now face criminal charges that remain before the courts.
In September 2012, Edmonton police chief Rod Knecht proposed that "excessive speeders" should have their vehicles seized and impounded, after a rash of high speeding drivers were charged, many driving 50 - 100km/hr over the speed limit.
The United Kingdom uses a variety of methods to enforce its road speed limits including average and instantaneous speed cameras, however eight counties are to switch off or remove cameras and a further two counties are considering such action.
There has also been debate as to whether the use of such cameras in order to force a driver to confess to the crime of speeding is in violation of European basic human rights; however, in 2007 the European Court of Human Rights, in O’Halloran and Francis v United Kingdom, found there was no breach of article 6 of the Human Rights Act 1998 in requiring the keepers of cars caught speeding on camera to provide the name of the driver, or to be subject to criminal penalty of an equivalent degree of severity if they failed to do so.
The number of designated traffic officers fell from 15–20% of Police force strength in 1966 to seven per cent of force strength in 1998, and between 1999 and 2004 by 21%. It is an item of debate whether the reduction in traffic accidents per 100 million miles driven over this time has been due to robotic enforcement. In the seven-month period following speed cameras in Oxfordshire being switched off in August 2010, fatalities increased from 12 to 18, a figure not out of line with the variation in fatalities over a ten-year period. Plans had been made to switch the cameras back on by November 2010, on the basis of increased speeds at camera sites, which occurred in April 2011. Oxfordshire had followed the lead of Swindon, which encountered a decline in casualties, serious injuries, and fatalities.
In the U.S. state of Ohio, the issue of whether a city has jurisdiction under the Ohio Constitution to issue citations based on speed cameras was heard by the Ohio Supreme Court on 18 September 2007, in the case of Kelly Mendenhall et al. v. The City of Akron et al. The court ruled in favor of Kelly Mendenhall.
Patagonia, Arizona has been cited on the National Motorists Association’s speedtrap.org website  as having one of the nation’s most active speed traps. City police regularly conceal their patrol cars behind trees along Arizona Highway 82 where motorists enter the city’s outskirts. The legal speed limit drops in a short space from 55 mph to 30 mph leading to some drivers who are not alert to be caught. The minimum fine for exceeding the posted speed limit even by 1 mph is $146.
Initially, Illinois used photo enforcement for construction zones only. There was legislation on the books to expand that throughout the state. However, Chicago has expanded its red light camera program and is planning to put speed cameras in school zones. Some suburbs (e.g. Alsip) already have cameras at various intersections.
Some U.S. states that formerly allowed red-light enforcement cameras but not speed limit enforcement cameras ('photo radar'), have now approved, or are considering, the implementation of speed limit enforcement cameras. The Maryland legislature approved such a program in January 2006. In 2005, 2006, 2008 and 2009 the California legislature considered, but did not pass, bills to implement speed limit enforcement cameras. Tennessee legislators are also considering expanding their speed limit enforcement cameras after successes in Chattanooga such as generating $158,811 in revenue in the first three months.
A 2007 study of speed cameras on the Arizona State Route 101 in Scottsdale found a 50% reduction in the total crash frequency, with injuries falling by 40% however rear-end collisions increased by 55%.
As of late 2008, cameras were placed along all Phoenix area freeways capturing drivers doing speeds greater than 11 mph over the posted speed limit. Over 100 new cameras were expected to be up and running by 2009.
As of 2009, speed cameras existed in 48 communities in the United States, including in Arizona, Colorado, Illinois, Iowa, Louisiana, Maryland, Massachusetts, New Mexico, Ohio, Oregon, Tennessee, Washington, and Washington, D.C.
In 2017, the National Safety Council graded states on road safety measures such as automated enforcement of speeding or red light cameras, interstate speed limits, and lower speed limits in school zones.
In the United States, it is common for all installation, operation, and verification procedures to be carried out by private companies that in some States receive payment based on the number of infringements they issue, and often under no testing regime whatsoever, however these units are required by law to take at least two pictures of each vehicle.
Opposition groups have formed in some locations where automated traffic enforcement has been used. In the US city of Scottsdale Arizona, an activist group CameraFraud was formed and staged sign-wave protests and petition drives to oppose the use of speed limit enforcement cameras ('photo radar'). In the 2008 elections in nearby Pinal County, Paul Babeau won an election for Sheriff after making a campaign promise to eliminate speed cameras.
It has been announced that Arizona will not renew its contract with Redflex, the company that operates the cameras. However, many towns in Arizona (e.g. Chandler, Mesa, Scottsdale, Paradise Valley, Superior) still have red light and/or speed cameras. Photo enforcement is illegal in the town of Gilbert, Arizona. Tempe, Arizona has removed all of their red light cameras. Baker, Louisiana still contracts with Redflex. This association is the subject of legislative action.
In France, the fixed speed cameras on motorways are announced with a sign about half to 2 km before: Pour votre sécurité, contrôles automatiques (For your safety, automatic controls) and marked in French motorway maps. On non-motorway roads, sometimes there is a sign however in other locations an electronic sign showing your speed may indicate a fixed speed camera further along the road. Average speed cameras now operate in some areas.
In Switzerland, it is strictly forbidden to announce speed controls. If the software of navigation equipment includes the locations of fixed speed cameras, the devices can be seized and destroyed. This also applies to mobile phones or handheld devices with the appropriate function.
In Germany, radar detectors are prohibited, however, current mobile controls are mentioned by some radio stations, which is not illegal.
In Spain and Portugal some device detect drivers who run too fast, and consequently close a traffic lights to stop them.
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I regard the abolition of the speed limit as the most important recommendation of the Royal Commission... Policemen are not stationed in the villages where there are people about who might be in danger, but are hidden in hedges or ditches by the side of the most open roads in the country... I am entirely in sympathy with what the noble Earl said with regard to police traps. In my opinion they are manifestly absurd as a protection to the public, and they are used in many counties merely as a means of extracting money from the passing traveller in a way which reminds one of the highwaymen of the Middle Ages.
a pocket-sized instrument is being produced by Marchant House Limited of New Street, Oadby, Liecester, to be used in motor vehicles to give instant warning of a police radar speed trap ... Anyone wishing to use this type of apparatus would require a licence under the Wireless Telegraphy Act, 1949. The firm in question has recently been informed that I am not prepared to issue a licence for such purposes
A notable example is in the Nottingham Safety Camera Pilot where virtually complete compliance was achieved on the major ring road into the city
Across all Nottinghamshire SPECS installations, KSI figures have fallen by an average of 65%
Camera sites had lower than expected numbers of injurious crashes up to 300 metres using circles and up to 500 metres using routes. Routes methods indicated a larger effect than the circles method except in the 100 metres nearest sites. A 500-metre route method was used to investigate the effect within strata of time after intervention, time of day, speed limit, and type of road user injured. The number of injurious crashes after intervention was substantially reduced
Existing research consistently shows that speed cameras are an effective intervention in reducing road traffic collisions and related casualties. The level of evidence is relatively poor, however, as most studies did not have satisfactory comparison groups or adequate control for potential confounders. Controlled introduction of speed cameras with careful data collection may offer improved evidence of their effectiveness in the future.
The main report says that fixed cameras reduce deaths and serious injuries by 50 per cent and mobile cameras by 35 per cent. It calculates that cameras prevent 1,745 deaths or serious injuries a year across Britain. But once the regression to the mean was taken into account, fixed cameras were found to reduce deaths and serious injuries by only 873, or 24 per cent for fixed and 17 per cent for mobile cameras. While still impressive, these reductions are lower than could be achieved by other road safety measures.
Support for speed cameras is running at an all-time high, a poll by the AA has suggested. According to the motoring organisation's survey of members in October, 75% now believe that the use of speed cameras is 'acceptable' – including 30% who believe their use is 'very acceptable'. This compares with a 69% approval rating in a poll conducted in November last year, and is the highest level reached in ten years of monitoring public sentiment for the devices, the AA says.
A Toronto man is upset he was ticketed for flashing his headlights to tip off oncoming drivers of a radar speed trap, especially since police admit the act is not illegal.'
A controversial decision by the AA to publish its first map of speed traps has provoked a storm of protest from safety experts, who accuse the organisation of encouraging motorists to break the law.