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A road speed limit is the maximum speed allowed by law for road vehicles. Speed limits are commonly set and enforced by the legislative bodies of nations or provincial governments, such as States within the USA.
In addition to setting a maximum speed limit, most governments also enforce speed limits which are relative to the driving conditions experienced, for instance drivers should adjust their maximum speed when driving in fog or heavy rain. For example, the California Civil Code 22350 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." This "basic rule", or similar legal language, applies whether or not maximum speed limits are in place (such as formerly in the US State of Montana). Some roads also have "minimum speed limits", where slow speeds are considered to impede traffic flow or be dangerous.
The first speed limit was the 10 mph limit introduced by the Locomotive Act of 1861 (or "Red Flag Act") in the United Kingdom (automobiles were in those days termed “light locomotives”). In 1865, the revised Locomotive Act reduced the speed limit to 4 mph in the country and 2 mph in towns. The 1865 Act required a man with a red flag or lantern to walk 60 yards ahead of each vehicle, enforce a walking pace, and warn horse riders and horse drawn traffic of the approach of a self propelled machine. The replacement of the "Red Flag Act" by the Locomotive Act of 1896, and the increase of the speed limit to 14 mph has been commemorated each year since 1927 by the London to Brighton Veteran Car Run.
Germany, Nepal, the Isle of Man and the Indian state of Uttar Pradesh are the only places in the world that do not have a general speed limit. Not including public roads which do not have a legal speed limit, the highest speed limit in the world is 160 km/h (100 mph), which has been experimentally applied on selected test stretches in Austria and the United Arab Emirates.[1]
Traffic engineers observe that the majority of drivers drive in a safe and reasonable manner, as demonstrated by consistently favorable driving records. A report from the British Columbia Ministry of Transportation includes in its summary the finding that the incidence of crashes depends more on variations in speed between vehicles than on absolute speed, and that the likelihood of a crash happening is significantly higher if vehicles are traveling at speeds slower or faster than the mean speed of traffic.[2]
Speed limits are set based on many factors, such as road features, crash records, legal statutes, administrative judgment, engineering judgment and political dictate. Two common measures for setting speed limits are the design speed of the road and the 85th percentile of travel speeds (See Design Speed, Operating Speed, and Posted Speed Practices).
In the United States the design speed is officially defined as "a selected speed used to determine the various geometric design features of the roadway", according to the 2001 American Association of State Highway and Transportation Officials highway design manual, commonly referred to as the "Green Book." Previous versions of the Green Book referred to design speed as the "maximum safe speed that can be maintained over a specific section of highway when conditions are so favorable that the design features of the highway govern"; however the 2001 edition removed the term "safe" in order to avoid the implication that speeds greater than the design speed were necessarily "unsafe."
Safe operating speeds can exceed the design speed. Example reasons include:
In commonly accepted engineering practice, design speed is considered a "first guess" at an appropriate speed limit.
In the United States, traffic engineers may rely on the 85th percentile rule[3] to establish speed limits. The speed limit should be set to the speed that separates the bottom 85% of vehicle speeds from the top 15%. The 85th percentile is slightly greater than a speed that is one standard deviation above the mean of a normal distribution.
The theory is that traffic laws that reflect the behavior of the majority of motorists may have better compliance than laws that arbitrarily criminalize the majority of motorists and encourage violations. The latter kinds of laws lack public support and often fail to bring about desirable changes in driving behavior. An example is the federally-mandated 55 mph (90 km/h) speed limit that was removed in part because of notoriously low compliance.
Most U.S. jurisdictions report using the 85th percentile speed as the basis for their speed limits, so the 85th-percentile speed and speed limits should be closely matched. However, a review of available speed studies demonstrates that the posted speed limit is almost always set well below the 85th-percentile speed by as much as 8 to 12 mph (see p.88) (13 to 19 km/h). Some reasons for this include:
For more information about traffic signs in general, see Traffic sign. The start of a speed limit is usually marked with a speed limit traffic sign. Speed limit signs can appear near borders and road intersections, and in some cases speed limit reminder signs appear at regular intervals. In the European Union, large signposts showing the national speed limits of the respective country are usually erected right after border crossings, with a repeater sign some 200 to 500 metres (about 650 to 1,650 ft) after the first sign. The same practice is followed in several U.S. states.
Occasionally, different units of speed measurement are used on each side of a border. For example, Northern Ireland (part of the UK) uses miles per hour (mph) for speed limits and miles for distance, whereas the Republic of Ireland uses kilometres per hour (km/h) for speed limits and kilometres for distance. The UK and the United States are the only major nations still using the customary (imperial) units system.
The US has shown no intention to convert to SI units, and, in fact, reverted to its current imperial units in states that had both imperial and SI systems such as California and Arizona. However, Ohio and South Dakota still have some SI distances and speeds on its exit distance and speed limit signs (such as 70 mph / 110 km/h, or 3 miles / 5 km to next exit). Houston, Texas has some signs in both imperial and SI units near its airports and downtown.
Design of speed limit signage varies between countries. In the European Union, the red circle is most common, while in North America, signs are usually rectangular. Australian speed limit signs are a combination, with a red circle inside a rectangular sign. Sometimes, speed limits are also painted on the road surface as a reminder.
The design of minimum speed signage also varies between countries. Most countries use blue circles based on obligatory signs. A Japanese minimum speed sign has the same design as a maximum speed sign but with a horizontal line below the number.
<gallery> Image:Zeichen 393.svg|Informational sign at German border crossings Image:Zeichen 274.1.svg|Zonal restriction, common in residential areas Image:Zeichen 274.2.svg|End of restricted zone Image:Speed limit 50 sign.svg|United States speed limit sign in miles per hour </gallery> <br clear="all" />
The following table shows the respective speed limits (excepting the local 30 km/h or lower limits in many countries) in km/h (except mph for the United Kingdom and the United States with km/h in parentheses):
<sup>*</sup>Motor routes: roads with two or more lanes (dual carriageway), a median, and a minimum speed of 60 km/h.<br>
Remarks: <br>∞ The Infinity symbol means that there is no speed limit. <br><sup>1</sup> 130 km/h is the recommended maximum speed on motorways, as indicated by a blue sign. Many sections of the German motorway network are now covered by speed limits, usually ranging from 80 to 130 km/h (140 km/h as speed limit is being tested in Lower Saxony -some politicians are against it, because 140 km/h is over the recommended maximum speed, depending on local conditions (i.e., frequent traffic, terrain, etc.). It is usual for drivers involved in crashes who were exceeding the 'recommended' speed limit to be held to be at least partly at fault, regardless of the circumstances of the crash, and insurance companies have the right to withhold payment. <br><sup>2</sup> On expressway where is indicated. <br><sup>3</sup> Two and three-lane expressways: 130 km/h; since 2003 on some three-lane expressway a 150 km/h limit was introduced, but actually it isn't operative). <br><sup>4</sup> Cars with heavy trailer: 80 km/h; lorries with heavy trailer: 70 km/h. <br><sup>5</sup> Cars with heavy trailer: 100 km/h; lorries with heavy trailer: 80 km/h. <br><sup>6</sup> During winter, when conditions are often bad, all Finnish motorways have a speed limit of 100 km/h or less. <br><sup>7</sup> Additional trailer checkup (TÜV) and special speed plaque required on vehicle. <br><sup>9</sup> A provisional increase of the speed limit on motorways from 90 to 100 km/h was made permanent when the number of accidents decreased. <br><sup>10</sup> Signs are posted in mph, a situation unlikely to change in the near future. <br><sup>11</sup> 100 km/h is default limit on all National Routes regardless of design standard when local limits do not apply; regional and minor routes have an 80 km/h limit. All limits are signposted either way. <br><sup>12</sup> Iceland does not have expressways/motorways in the traditional sense. There is really only one such road, with three and four lanes and no traffic lights. It is within city limits, and the maximum speed is 80 km/h. <br><sup>13</sup> 60 km/h in built-up areas between 11 pm and 5 am. Out of built-up areas between 90 and 110 km/h depending on how many lanes the road has, whether it is single or dual carriageway, and whether it is signed an expressway or not. <br><sup>14</sup>A provisional increase to 160 km/h was in place on a 12 km stretch on the A10 in May and June 2006. <br><sup>15</sup> Built up area speed limit of 50 km/h in all states and territories except for the Northern Territory, where it remains at 60 km/h. Western Australia and the Northern Territory have a rural limit of 110 km/h. The Northern Territory has zoned some rural highways at 130 km/h. See separate article for details. <br><sup>16</sup> Speed limit is 110 km/h in several provinces, 100 km/h in others. <br><sup>17</sup> The state of Chihuahua posts a 100 km/h limit on the Autopistas (toll roads) within the state, other states allow up to 110 km/h on Autopistas. <br><sup>18</sup> The speed limit on Malaysian federal and state roads has been reduced to 80 km/h during festive seasons, starting from the 2006 Hari Raya Aidilfitri. <br><sup>19</sup> The state of Hawaii posts a 55 mph speedlimit on all stretches of "Interstate" highways. <br><sup>20</sup>Some states require vehicles towing trailers to follow the posted truck speed limit.
In some countries in Europe, traffic calming is gradually becoming a regular part of urban traffic management, after a long evolution of opinions and attitudes towards car use and vulnerable road users. From 1980 regulations for 30 km/h zones were enacted and have been widely applied. New urban policies have been defined with a view to encouraging a switch from car use to public transport and non-motorised modes (cycling, walking), with the additional condition of lower speeds to improve safety of vulnerable road users, for example national policies such as "Sustainable Safety" in the Netherlands or "Vision Zero" in Sweden.
On French autoroutes there is a variable speed limit: in dry weather, 130 km/h (80 mph); when raining, 110 km/h (68 mph). In 2005, a governmental report advised lowering the higher speed to 115 km/h (71 mph) in order to save fuel and reduce accident risks, but this proposal was badly received. Since 2002, the French government has installed a number of automatic radar guns on autoroutes, routes nationales, and other major thoroughfares. These are in addition to radar manned by the French National Police or Gendarmerie. The French authorities have credited this increase in traffic enforcement with a 21% drop in road fatalities from 2002 to 2003.
German autobahns are famous for having no universal speed limit, although about 30 % of them have posted speed limits[4] and about 10 % are equipped with motorway control systems that can show variable speed limits.[5] There is no national speed limit, either, for cars travelling on rural roads with a central reservation or a minimum of two marked lanes per direction. On such roads, however, an advisory speed limit (Richtgeschwindigkeit) of 130 km/h (80 mph) applies. While driving at higher speeds is not an offence, the increased risk induced by higher speeds (erhöhte Betriebsgefahr) may result in partial liability for damages. On all of these roads, there are speed limits for lorries, buses, and cars towing trailers.
While speeds over 200 km/h (124 mph) are not uncommon, most drivers choose much lower speed around 130 to 150 km/h (80 to 93 mph). Speed is also limited by traffic density and the type of the car - those with smaller engines often cannot exceed 180 to 200 km/h (110 to 120 mph) and most German manufacturers (excluding, notably, Porsche) deliberately limit the maximum speed of their more powerful automobiles to 250 km/h (155 mph). In the daytime, it is often impossible to drive at high speeds for more than a few kilometres. Rising fuel prices have also restricted the appeal of high-speed driving.
The introduction of a national speed limit for motorways and similar roads has been on the agenda of various political and environmentalist groups for decades, but at present, there are still no definite plans on behalf of the federal government regarding the matter. The Umweltbundesamt (Federal Environmental Agency) repeated its recommendation of such regulation in early 2007, but the current Merkel administration sees no need for it.
On rural roads that are neither motorways nor multi-lane roads as described above, there is a national speed limit of 100 km/h (60 mph). Lower speed limits apply to lorries, some buses, and cars towing trailers.
There is a general speed limit within city limits of 50 km/h (30 mph) but residential areas usually have a lower posted speed limit of 30 km/h (20 mph). On arterial roads, the speed limit may be raised to 60 or 70 km/h (37 to 43 mph).
In the Republic of Ireland, since 2004, the speed limit of motorways has been 120 km/h.[6] Dual carriageways generally have a limit of 100 km/h, but under local by-laws, stretches of dual carriageway described as High Quality Dual Carriageway can also have a speed limit of 120 km/h.[7] Other National primary and national secondary roads have a speed limit of 100 km/h,[8] while regional roads have a limit of 80 km/h.[9] Again, this 80 km/h can be increased due to local by-laws. [10] The limit on built-up areas is generally 50 km/h,[11] but may be increased to 60 km/h or, rarely, reduced to 30 km/h.[10] The conversion of limits to km/h from mph was effected by the 2004 Road Traffic Act.[12] The conversion of speed limit signposts to km/h occurred on 19 January 2005.
Italian Autostrade have a 130 km/h speed limit (80 mph), with 110 km/h (70 mph) limits on curvy roads and in rainy conditions. A 150 km/h (95 mph) limit straighter roads with at least three lanes per direction is allowed by regulations but has not yet been implemented. When there is rain, the Speed Limit goes down to 110 km/h on all Autostrade.
Since May 2002, the Netherlands has been experimenting with 80 km/h (50 mph) zones on motorways crossing suburban areas. The first zone to be implemented was on the A13, connecting Rotterdam to the Hague, at the Rotterdam suburb of Overschie. This was generally accepted as a success, so in 2005, the experiment was expanded, with four new zones in Rotterdam, the Hague, Utrecht and Amsterdam. DCMR report (Dutch). The new zones have had mixed results, causing great controversy and calls for the removal of them.
Norway has two general speed limits, 50 km/h in dense populated areas, and 80 km/h in sparsely populated areas. On some of the best motorways around the capital, Oslo, the speed is 100 km/h. The speed limits are strictly enforced, and the fines range from around $300 to $1200.
Sweden has the official limits 50 km/h in built-up areas, 70 km/h outside and 110 km/h on motorways. Usually main roads have 90 km/h outside built-up areas, and often 110 km/h in northern Sweden. Main roads in built-up areas separated from pedestrians usually have 70 km/h. From about 2000 signs have been introduced showing start and end of built-up area. They mean 50 and 70 if there is no number sign. Before that all speed limits were signposted with the round speed limit sign with a number.
From about 1990 to 1995, Sweden lowered the limit in the large city provinces from 110 km/h (70 mph) to 90 km/h (55 mph), which was the lowest in Europe at the time, citing environmental reasons. The term "large city province" was defined as a province including one of the three large cities with suburbs. That meant that the west coast motorway E6 had a 90 km/h (55 mph) limit on its (then) about 250 km of motorway, but some ordinary roads in less densely populated provinces had a 110 km/h (70 mph) limit. This reduced limit was later removed because it was neither popular nor well obeyed.
Soon, the speeds 40, 60, 60, 80, 100 and 120 km/h will be put on Swedish roads, in addition to the ones already in place.
Swiss Autobahnen, Autoroutes and Autostrada are limited to 120 km/h (75 mph). Semi-motorways, known as "motor roads", Autostrassen or [semi-autoroutes] generally have a limit of 100 km/h (60 mph).
From 1930 to 1965, most roads outside urban areas, including motorways, did not have a speed limit. However, in December 1965, after a series of multiple crashes on motorways, mainly in fog, an experimental speed limit of 70 mph (112 km/h) was introduced for motorways and all other unrestricted roads,[13] and made permanent in 1967 for motorways and dual carriageways with a central reservation (with the limit dropped to 60 mph for other unrestricted roads). It was reduced to 50 mph (80 km/h) in response to the 1973 oil crisis, and restored to 70 mph (112 km/h) in 1974. The Association of British Drivers has called for the limit to be increased. The opposition Conservative Party is proposing to raise the limit to 80 mph (130 km/h) where appropriate. The speed limits were established based on the performance of a selection of typical British 1960s vehicles, as evaluated by the UK Transport Research Laboratory. It is argued that modern cars and drivers are far more capable than those of four decades ago.
American speed limit signs usually read "SPEED LIMIT XX", such as "SPEED LIMIT 50" for 50 mph (80 km/h). A minimum speed sign reads "MINIMUM SPEED XX", such as "MINIMUM SPEED 45" for 45 mph (70 km/h). Speed limits on United States roads are usually:
Speed policy is determined by each state, allowing certain variances.
The US Department of Transportation is reviewing a proposal to institute a nationwide 68 mph (110 km/h) speed limit on commercial trucks in the US. The law would require all trucks made after 1990 with electronic engine controls to have their speed limiter set to 68 mph through their engine management software.
Since 1977, Canadian speed limits have been in km/h - they were previously in mph. A sign reads "MAXIMUM XX", such as "MAXIMUM 80" for 80 km/h. A minimum speed sign reads "XX MINIMUM", such as "60 MINIMUM" for 60 km/h. Typical speed limits are:
Note that where more than one limit is given per road, it usually indicates a difference between provinces; however, within provinces, different roads of the same classification have different speed limits. For example, in Alberta and Nova Scotia some freeways have a limit of 100 km/h, while others have a speed limit of 110 km/h (70 mph). In Ontario, all freeways have a maximum speed limit of 100 km/h unless there is a lower posted limit, although they generally operate at much higher speeds with very little enforcement. Speed limits are generally lower in Ontario and Quebec on comparable roads than in other Canadian provinces, except perhaps British Columbia. Examples of this disparity include rural two-lane highways in Ontario which have a standard speed limit of 80 km/h, while comparable roads in other provinces have standard speed limits of 90–100 km/h. In rural western Ontario, however, some two-lane roads have speed limits of 90 km/h.
In British Columbia, a review of speed limits conducted in 2002 and 2003 for the Ministry of Transportation found that posted limits on investigated roads were unrealistically low for 1309 km and unrealistically high for 208 km. The reports recommended to increase speed limits for multi-lane limited-access highways constructed to high design standards from 110 km/h to 120 km/h.[14] As described in that report, the Ministry is currently using "...Technical Circular T-10/00 [...] to assess speed limits. The practice considers the 85th percentile speed, road geometry, roadside development, and crash history."
In most Canadian provinces, as in most other locales, speed violation fines are double (or more) in construction zones, although in Ontario this only applies if workers are present in the construction zone.
Previously, all expressways in the People's Republic of China were limited to 110 km/h (68 mph). With the passage of the PRC's first road-related law, the Road Traffic Safety Law of the People's Republic of China, the speed limit was raised to 120 km/h (75 mph) from May 1, 2004; however, the updating of signs will still take some time.
Semi-expressways and city express routes (called kuàisù gōnglù () in Chinese, meaning "high speed public road") generally have lower speed limits of 100 km/h (62 mph): in some cases the speed limit may be lower.
On China National Highways (which are not expressways), a common speed limit is 80 km/h (50 mph). In localities, speed limits may drop to 40 km/h (25 mph).
In reality, few people drive according to the speed limits, and on most roads, enforcement cameras are non-existent. Where an enforcement camera does exist, it is marked "speeding detection camera" ().
On some designated "fast through routes" in cities, speed limits are up to 80 km/h (50 mph). Otherwise, speed limits are 70 km/h (44 mph) on roads with two uninterrupted yellow lines and 60 km/h (37 mph) or 50 km/h (30 mph) otherwise. Signage in towns and on expressways is often present.
Minimum speed limits on expressways vary. A general minimum speed limit of 60 km/h (37 mph) is in force at all times (although traffic jams more than thwart it). The maximum speed limit, as posted on Chinese motorways is 120 km/h (75 mph). This is a recent change.
Many expressways in Hong Kong are limited at 80 km/h, with Tolo Highway and West Kowloon Highway having a 100 km/h limit, and North Lantau Highway limited at 110 km/h, the highest speed limit in Hong Kong.
Speed limits in India vary by state and vehicle type. Motorcycles are limited to 50 km/h on all roads, while trucks and buses are restricted to 65 km/h. The limits on cars range from 80 km/h in Maharashtra, 50-60 km/h in New Delhi, and none at all in Uttar Pradesh. Nationwide laws have been proposed to set a 100 km/h speed limit for cars and to increase to the limit of motorcycles to 65 km/h.[15]
It is common to see speeds of 100-120 km/h on expressways, of which there are very few in India, the most notable being the Mumbai-Pune Expressway. Motorcycles are not allowed to use expressways due to safety reasons. The speed limit on the Mumbai-Pune Expressway is 80 km/h, but on other ones the limit is 120 km/h. Bangalore's Airport expressway, opening in 2008, will have a 180 km/h speed limit.[16]
Speed limit enforcement has historically been lax on expressways. However, highway police now use automated instruments which capture the speed and mail the fine to the car's owner. Failure to pay may result in doubling of the fine, cancellation of the driving license, and even arrest. Police are now also using wireless PDAs to identify a driver's or vehicle's history, allowing the officer to take appropriate action. There has been an increase in patrol units, up to 500 from 75.
Indonesia employes a maximum and minimum speed limit. The general maximum speed limit on tollways and highways are 80-100 km/h. On all other roads, it is 40-60 km/h. Minimum speed limit is 20 km/h lower than the posted maximum.
However, enforcement of speed limit is rare and drivers often follow "reasonable and prudent" speed limit guideline.
The general limit is 60 km/h except for divided national highways where the limit is 100 km/h. Urban areas are usually zoned at 40 km/h. Limits in Japan are different from most countries by:
The speed limit in Malaysia is 110 km/h on closed toll expressways. Speed limit on federal, state and municipal roads is between 50 km/h and 90 km/h depending on geographical factors along the road. The default speed limit is 90 km/h and it is reduced to 60 km/h in urban areas. The highway police monitor the speed of passing cars from beneath a bridge or signboard.
Several years ago, a proposal to increase the speed limit on Malaysian expressways to 140 km/h was made but was finally rejected in 2005 by Minister of Works, Datuk Seri S. Samy Vellu, stating that most drivers often drive 10 to 30 km/h faster than the stated speed limit on the expressways.
Starting from the 2006 Hari Raya Aidilfitri festive season, a new lower speed limit for festive seasons of 80 km/h has been implemented on federal and state roads as a preventive measure to reduce accidents during festive seasons.
Philippine expressway speed limits are based on the US Interstate Highway standards. The general speed limit in the Philippines is 60 km/h as its minimum and 100 km/h is maximum, although 120 km/h is still allowed.
Despite all of these and other advanced equipment to catch speeders, overspeeding is still rampant.
The Act Governing the Punishment of Violation of Road traffic Regulations (道路交通管理處罰條例) is the basic law. The Road Traffic Security Rules (道路交通安全規則) are the basic administrative regulations. When no other limits are posted, the default speed limits are:
Speed limits on freeways are posted by signs, generally 100 km/h. Limited segments are posted at 90, 80, or 70 km/h. Most segments of the National Highway No. 3 are now posted at 110 km/h, the highest speed limit in Taiwan. A truck with a gross weight of 20 tonnes or more is limited to 90 km/h. Except on approaches to toll stations and work areas, minimum speeds are usually posted at 60 km/h.
Australian states and territories use a combination of default speed limits and speed zones. The default limits apply in the absence of a speed zone and are:
Speed limits in New Zealand range up to and including 100 km/h. The most commonly seen are:
These speed limits are less seen, but they do exist:
Signage tends to follow the European model of a number inside a red circle. Sometimes "open road limit" occurs as a black forward slash inside a thin black ring (similar to the UK's National Speed Limit sign).
The letters LSZ (Limited Speed Zone) indicate that the limit is 100 km/h unless conditions (visibility, road condition, rain, many other road users) would make this unwise, in which case it is 50 km/h. This type of speed limit can no longer be set since 2003, and are progressively being replaced, mostly with 70 km/h limits.
A local bylaw in Auckland produced the curious speed limit of 16 km/h in Waikumete Cemetery. When New Zealand converted from Imperial to metric measure, the statues concerning speed in this location were not updated even though the signage legally had to be altered from Imperial units. This limit existed into the early 21st century. Typically speeds in such areas were 10, 15, or 20 km/h after adoption of the metric system.
There is no minimum speed limit but vehicles traveling less than the maximum and are followed by other vehicles must keep to the side of the road and pull over to allow others to pass as soon as is safe.
Some vehicles are restricted to lower overall speed limits:
There are also variable speed limits in some areas, such as school zones.
The general speed limits in Namibia are (according to Road Authority of Namibia):
The general speed limits in terms of the South African National Road Traffic Act, 1989 and its Regulations are:
Prior to the invention of radar, speed limits were normally enforced by clocking vehicles travelling through speed traps. Clocking a vehicle simply means timing how long it takes for the automobile to pass between two fixed landmarks along a roadway, from which the vehicle's average speed could easily be determined. Setting up a speed trap that could provide legally satisfactory evidence was usually time consuming, however, and early speed traps were often difficult to hide. As a result, organizations such as the Automobile Association could often keep fairly accurate records of speed trap locations.
In the early 21st century, police used radar, laser range-finders, planes, and automated devices. Officers may also use a method called pacing: following a car for a certain time to establish speed using the calibrated speedometer of the patrol car. Recently, Automatic Number Plate Recognition (ANPR) camera systems have been used which time a vehicle between long sections of road (approximately one mile), calculating the average speed between two points. This method eliminates the risk of heavy braking at the locations of conventional speed cameras, but may raise privacy issues.
In several countries, notably the Netherlands and the United Kingdom, an increase in automated speed enforcement has resulted in a significant increase in the number of fake number plates. In France, the use of automated enforcement has been credited with contributing to a substantial reduction in fatalities.[17] Most Western European countries now use automated enforcement on at least some roads.
Speed limit policy can affect enforcement. According to 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[.]"[18]
Speed limit enforcement often begins at a small amount above the speed limit. For example, speeding citations for 1 unit (mph or km/h) above the limit are exceedingly rare. In certain cases, such as Houston, Texas, only 1% of speeding citations are for less than 10 mph (16 km/h) above the speed limit (Houston Chronicle, "It's really true: Drivers going less than 10 mph over limit rarely ticketed", November 24, 2002).
In the United States, speeding enforcement tolerance is usually up to the discretion of the arresting officer. A small tolerance is almost always allowed even where traffic signs advise "NO TOLERANCE." Some states have official tolerances, such as Pennsylvania. As per state law, one cannot be cited by an officer using a radar/laser gun for traveling less than 10 mph over a speed limit of less than 55 mph or for traveling less than 6 mph over a speed limit of 55 mph or greater.[19]
In Taiwan, even though the Regulations on Establishing Traffic Signs and Indicating Lines (()路交通標誌標線號誌設置規則) define the speed limit signs to show absolute limits, the police agencies have generally agreed a tolerance of up to 10 km/h. A notable exception was the Hsuehshan Tunnel opened on June 16, 2006 with automated speeding cameras. After the zero tolerance on speeding created controversy,[20] effective 00:00 (UTC+8) on September 16, 2006, a tolerance of 10 km/h has been allowed in the same way as other Taiwanese roads. [11]
In the United Kingdom ACPO guidelines[12] recommend a tolerance level of the speed limit "+10% +2 mph" (e.g. a tolerance level in a 30mph zone of 35mph). However, each police force or safety camera partnership has the ability to use their discretion when setting the levels at which drivers will be prosecuted.
Road safety improvements in the Australian state of Victoria are largely contributed to infrastructure improvements and speed management including tougher tolerances and enforcement. Low level speeding is targeted because of the overall population effects. This is best explained by the recent Auditor General's independent review[21] which cites:
<blockquote>The relative risk of casualty crash involvement for vehicles travelling only a few km/h above the speed limit is lower than for those travelling a greater amount above the limit. However the contribution of “low level speeders” to the total number of casualty crashes is high because of the high number of motorists travelling at these speeds. Therefore, “low level speeding” represents a substantial risk across the road network.[22]</blockquote>
Victoria has some of the tightest speeding tolerances in Australia, with 3 km/h if the speed is under 100 km/h, or 3% if over 100 km/h. This is despite the fact that the Australian Design Rules stipulate that a car's speedometer must be accurate within a 10% tolerance.
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 at impact,[23] rising much faster than kinetic energy.
To illustrate these statistics, suppose two vehicles crash into a massive, fixed object, and one vehicle’s speed is 10% greater than the other vehicle. The faster vehicle will release 21% more energy, and its occupants will experience a 46% higher probability of a fatality.
It should be noted that crashes with dramatic, sudden speed changes that terminate almost all velocity are atypical. These kinds of crashes include head on collisions or collisions with massive, fixed objects like trees or concrete bridge piers.
Although the basic relationship between vehicle speed and crash severity is unequivocal and based on the laws of physics, the probability of a crash as well as crash severity can be mitigated. Safety devices like crash attenuators, barriers, or wide medians are examples. The highest degree of mitigation is found on motorways (which may be called freeways, limited access highways, also Autobahns, Interstates or other national names), which are internationally documented as being the safest roads per mile travelled despite their higher speeds, due to designing out of most conflict opportunities as well as restricted access.
The 1998 Synthesis of Safety Research Related to Speed and Speed Management sponsored by the US Federal Highway administration found, "on freeways and other high-speed roads, speed limit increases generally lead to higher speeds and crashes."[24] Increasing a speed limit by 4 mph (6 km/h) would increase the average speed by 1 mph (1.6 km/h) and increase injury accidents by 5%. The report cautions that "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." The report noted that traffic calming significantly reduced speeds and injuries in treated areas but that the decrease may be due to reduced traffic volumes. The report also suggests that "variable speed limits that adjust with traffic and environmental conditions could provide potential benefits" as most of the speed related crashes involve speed too fast for conditions.
The report noted the landmark study (D. Solomon, "Accidents on Main Rural Highways Related to Speed, Driver, and Vehicle", Federal Highway Administration, Washington, DC, July 1964) that observed a "U-shaped curve" of crash probability versus speed, where crash rates were lowest for travel speeds near the mean speed of traffic, and increased with greater deviations above and below the mean. Subsequent research has found that "The occurrence of a large number of crashes involving turning maneuver partly explains the increased risk for motorists traveling slower than average and confirms the importance of safety programs involving turn lanes, access control, grade separation, and other measures to reduce conflicts resulting from large differences in travel speeds."
Some safety factors are not always under the full control of the driver, such as driver alertness and distractions, road conditions, weather, daylight availability, actions and alertness of other drivers, and wildlife. While these factors are not directly related to vehicle speed, the effects of these factors can be more severe with more speed. For example, a deer running across the road has no consequences to a parked vehicle but could have disastrous consequences for a vehicle traveling at 100 mph (160 km/h). This suggests that lower speeds can reduce the frequency and severity of crashes; lower speeds can give the driver more time to respond appropriately in the face of unexpected dangers, and it can reduce the severity of a crash should one happen. However, since the efficacy of speed limits in restraining driver speed is subject to debate, it is not clear how well speed limits can ameliorate these other factors.
Another view is that, while speed can play a part of the causal chain which leads to crashes, speed's role is mostly to magnify the consequences of other unsafe acts. This viewpoint is reinforced by the fact that speed is rarely the sole crash factor. In many cases, removing the other crash factors, such as a right of way violation, would have absolutely prevented the collision. While reducing the speed could have a beneficial effect on the severity and probability of the crash, it usually cannot guarantee crash prevention.
Most 'speed-related' crashes involve speed too fast for conditions such as limited visibility or reduced road traction, rather than in excess of the posted speed limit. Most speed-related crashes occur on local and collector roads with relatively low speed limits. However, most speed-related traffic citations involve speeds in excess of posted maximum speed limits. Variable speed limits (q.v.) offer some potential to reduce speed-related crashes, but due to the high cost of implementation exist primarily on motorways. Speed-related crashes can occur on high speed limit roads at low speeds, e.g. below 30 mph; for example, truck rollovers on exit ramps.
Recently some jurisdictions have begun experimenting with variable speed limits which change with road congestion and other factors (this is distinct from France's reduction of limits during adverse weather). One example is on Britain's M25 motorway, which circumnavigates London. On the most heavily-traveled 22-km section (junction 10 to 16) of the M25 variable speed limits combined with automated enforcement have been in force since 1995. Initial results of the 1995 trial indicated savings in journey times, smoother flowing traffic and a fall in the number of accidents, so the trial implementation was made permanent in 1997. Further trials on M25 have been thus far proved inconclusive.[25]
In Germany, first experiments with variable signs took place in 1965 on A8 Munich-Salzburg with signs that were operated manually.[26] Beginning in the 1970s, more and more advanced Streckenbeeinflussungsanlagen (linear 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. By 2007, 1200 km (10 %) of German motorways will be equipped with such systems.[5]
In 2006, Austria began experimenting with a 160 km/h (100 mph) speed limit on a selected test stretch of Autobahn as part of their program of variable speed limit, using the slogan "flexibility with responsibility."
New Zealand has had variable speed limits since 2001. The first installation was on the Ngauranga Gorge, a steep section of dual carriageway on SH1 north of the capital, Wellington. The speed limit is normally 80 km/h. The downhill section is monitored by a fixed speed camera.
In The Netherlands, much of the dense motorway network is equipped with variable speed regulation systems such as DRIP. The electronic signage is commonly posted every 500 metres. The system keeps track of all traffic movement and lowers the speed limit in case it measures the start of traffic congestion. When activated the speed limit usually is 100 km/h but can be set at 90, 70 or 50 km/h according to the level of expected traffic congestion.
Variable speed limits are used on some stretches of highway in the United States, but it has not been implemented on a national basis. On Interstate 90 at Snoqualmie Pass, Washington, (near Seattle) variable speed limits are used to slow traffic in severe winter weather. This is also done on other mountain passes in Washington.[27] Variable speed limit signs, in combination with variable message signs, have been in use for decades on the New Jersey Turnpike, where officials can adjust the speed limit according to weather, traffic conditions, and construction.
Speed limits and their enforcement have been opposed by some motorists since their inception. Britain's first motoring organization, the AA, was formed to warn members about speed traps. Other organizations, such as the Association of British Drivers, Safe Speed, the North American National Motorists Association, and German Auto Club ("ADAC"), have sought to ban or discredit certain speed limits as well as other measures, such as automated camera enforcement. The debate over speed limit enforcement has become a large part of the road safety and environmental policy debate in some countries.
Critics of speed limits and strict enforcement outside built-up areas point to:
Prior to the (now defunct) 1974 national 55 mph (88 km/h) speed limit in the U.S., German Autobahns had a higher fatality rate than U.S. Interstates; however, a few years later, the Autobahn rate fell below that of (then) 55 mph (88 km/h) limited U.S. Interstates. IRTAD records show the U.S. rate remains higher than that on the largely unrestricted German Autobahn network. While the fatality rate on the UK's 70 mph (112 km/h) speed-limited motorways is about half of Germany's, the 60 mph (96 km/h) limit in rule-conscious Japan corresponds to a motorway fatality rate greater than Germany's. However, simple comparisons of fatality rates between countries neglect to account for differences in traffic density, quality of medical care, and Smeed's law.
In some juristictions some public roads have no speed limits:
Montana has had a speed limit since June 1999 - see the Montana section of the Speed limits in United States page for more information. Australia's Northern Territory had no blanket speed limits outside major towns, until January 2007, when rural speed limits reduced to 110 km/h or 130 km/h.[33]
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