Speed limit
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Speed limits on road traffic, as used in most countries, set the legal maximum speed at which vehicles may travel on a given stretch of road.[1] Speed limits are generally indicated on a traffic sign reflecting the maximum permitted speed, expressed as kilometres per hour (km/h) or miles per hour (mph) or both. Speed limits are commonly set by the legislative bodies of national or provincial governments and enforced by national or regional police and judicial authorities. Speed limits may also be variable, or in some places nonexistent, such as on most of the Autobahnen in Germany.[2]
The first numeric speed limit for automobiles was the 10 mph (16 km/h) limit introduced in the United Kingdom in 1861.[3]
As of 2018[update] the highest posted speed limit in the world is 160 km/h (99 mph), applied on two motorways in the UAE.[4] Speed limits and safety distance are poorly enforced in the UAE, specifically on the Abu Dhabi to Dubai motorway – which results in dangerous traffic, according to a French government travel advisory.[5] Additionally, "drivers often drive at high speeds [and] unsafe driving practices are common, especially on inter-city highways. On highways, unmarked speed bumps and drifting sand create additional hazards", according to a travel advisory issued by the U.S. State Department.[6]
There are several reasons to regulate speed on roads. It is often done in an attempt to improve road traffic safety and to reduce the number of casualties from traffic collisions. The World Health Organization (WHO) identified speed control as one of a number of steps that can be taken to reduce road casualties.[n 1] As of 2021, the WHO estimates that approximately 1.3 million people die of road traffic crashes each year.[7]
Authorities may also set speed limits to reduce the environmental impact of road traffic (vehicle noise, vibration, emissions) or to enhance the safety of pedestrians, cyclists, and other road-users. For example, a draft proposal from Germany's National Platform on the Future of Mobility task force recommended a blanket 130 km/h (81 mph) speed limit across the Autobahnen to curb fuel consumption and carbon emissions.[8] Some cities have reduced limits to as little as 30 km/h (19 mph) for both safety and efficiency reasons.[9] However, some research indicates that changes in the speed limit may not always alter average vehicle speed.[10] Lower speed limits could reduce the use of over-engineered vehicles.[11]
History
[edit]![]() | The examples and perspective in this section may not represent a worldwide view of the subject. (August 2015) |
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In Western cultures, speed limits predate the use of motorized vehicles. In 1652, the American colony of New Amsterdam passed a law stating, "No wagons, carts or sleighs shall be run, rode or driven at a gallop". The punishment for breaking the law was "two pounds Flemish", the equivalent of US $50 in 2019.[12] The 1832 Stage Carriage Act introduced the offense of endangering the safety of a passenger or person by "furious driving" in the United Kingdom (UK).[13] In 1872, then-President of the United States Ulysses S. Grant was arrested for speeding in his horse-drawn carriage in Washington, D.C.[14][15]
A series of Locomotive Acts (in 1861, 1865 and 1878) created the first numeric speed limits for mechanically propelled vehicles in the UK; the 1861 Act introduced a UK speed limit of 10 mph (16 km/h) on open roads in town, which was reduced to 2 mph (3 km/h) in towns and 4 mph (6 km/h) in rural areas by the 1865 "Red Flag Act".[16] The Locomotives on Highways Act 1896, which raised the speed limit to 14 mph (23 km/h) is celebrated by the annual London to Brighton Veteran Car Run.[citation needed]
On 28 January 1896, the first person to be convicted of speeding is believed to be Walter Arnold of East Peckham, Kent, UK, who was fined 1 shilling plus costs for speeding at 8 mph (13 km/h).[17][18][19]
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In 1901, Connecticut was the first state in the United States to impose a numerical speed limit for motor vehicles, setting the maximum legal speed to 12 mph (19 km/h) in cities and 15 mph (24 km/h) on rural roads. Speed limits then propagated across the United States; by 1930 all but 12 states had established numerical limits.[12]
In 1903, in the UK, the national speed limit was raised to 20 mph (32 km/h); however, as this was difficult to enforce due to the lack of speedometers, the 1930 "Road Traffic Act" abolished speed limits entirely. In 1934, a new limit of 30 mph (48 km/h) was imposed in urban centers, and in July 1967, a 70 mph (110 km/h) national speed limit was introduced.[21]
In Australia, during the early 20th century, there were people reported for "furious driving" offenses. One conviction in 1905 cited a vehicle furiously driving 20 mph (32 km/h) when passing a tram traveling at half that speed.[22]
In May 1934, the Nazi-era "Road Traffic Act" imposed the first nationwide speed limit in Germany.[citation needed]
In the 1960s, in continental Europe, some speed limits were established based on the V85 speed, (so that 85% of drivers respect this speed).[23]
In 1974, Australian speed limits underwent metrication: the urban speed limit of 35 mph (56 km/h) was converted to 60 km/h (37 mph); the rural speed limits of 60 mph (97 km/h) and 65 mph (105 km/h) were changed to 100 km/h (62 mph) and 110 km/h (68 mph) respectively.[24]
In 2010, Sweden defined the Vision Zero program,[23] a multi-national road traffic safety project that aims to achieve a highway system with no fatalities or serious injuries involving road traffic.
Regulations
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Most countries use the metric speed unit of kilometres per hour, while others, including the United States, United Kingdom, and Liberia, use speed limits given in miles per hour.
Vienna Convention on Road Traffic
[edit]In countries bound by the Vienna Conventions on Road Traffic (1968 & 1977), Article 13 defines a basic rule for speed and distance between vehicles:[25]
Every driver of a vehicle shall in all circumstances have his vehicle under control to be able to exercise due and proper care and to be at all times in a position to perform all manœuvres required of him. He shall, when adjusting the speed of his vehicle, pay constant regard to the circumstances, in particular the lie of the land, the state of the road, the condition and load of his vehicle, the weather conditions and the density of traffic, so as to be able to stop his vehicle within his range of forward vision and short of any foreseeable obstruction. He shall slow down and if necessary stop whenever circumstances so require, and particularly when visibility is not excellent.
Reasonable speed
[edit]Most legal systems expect drivers to drive at a safe speed for the conditions at hand, regardless of posted limits.
In the United Kingdom, and elsewhere in common law, this is known as the reasonable man requirement.[26]
The German Highway Code (Straßenverkehrs-Ordnung) section on speed begins with the statement (translated to English):[27]
Any person driving a vehicle may only drive so fast that the car is under control. Speeds must be adapted to the road, traffic, visibility and weather conditions as well as the personal skills and characteristics of the vehicle and load.
In France, the law clarifies that even if the speed is limited by law and by local authority, the driver assumes the responsibility to control a vehicle's speed, and to reduce that speed in various circumstances (such as when overtaking a pedestrian or bicycle, individually or in a group; when overtaking a stopped convoy; when passing a transportation vehicle loading or unloading people or children; when the road does not appear clear, or risky; when visibility is low, etc.).[28] If drivers do not control their speed, or do not reduce it in such cases, they can be penalized. Other qualifying conditions include driving through fog, heavy rain, ice, snow, gravel,[29] or when drivers encounter sharp corners, a blinding glare,[30] darkness, crossing traffic,[31] or when there is an obstructed view of orthogonal traffic—such as by road curvature, parked cars, vegetation, or snow banks—thus limiting the Assured Clear Distance Ahead (ACDA).[32][33]
In the United States, this requirement is referred to as the basic rule,[34] as outlined by US federal government law (49 CFR 392.14[35]), which applies in all states as permitted under the commerce clause and due process clause.[36][37] The basic speed law is almost always supplemented by specific maximum or minimum limits but applies regardless. In California, for instance, Vehicle Code section 22350 states that "No person shall drive a vehicle upon a highway at speed greater than is reasonable... and in no event at a speed which endangers the safety of persons or property".[38] The reasonable speed may be different than the posted speed limit. Basic rule speed laws are statutory reinforcements of the centuries-old common law negligence doctrine as specifically applied to vehicular speed.[39] Citations for violations of the basic speed law without a crash[40] have sometimes been ruled unfairly vague or arbitrary, hence a violation of the due process of law, at least in the State of Montana.[41] Even within states, differing jurisdictions (counties and cities) choose to prosecute similar cases with differing approaches.[42]
Excessive speed
[edit]Consequential results of basic law violations are often categorized as excessive speed crashes; for example, the leading cause of crashes on German autobahns in 2012 fell into that category: 6,587 so-called "speed related" crashes claimed the lives of 179 people, which represented almost half (46.3%) of 387 autobahn fatalities in 2012.[43] However, "excessive speed" does not necessarily mean the speed limit was exceeded, rather that police determined at least one party traveled too fast for existing conditions.[43][44][45] Examples of conditions where drivers may find themselves driving too fast include wet roadways (due to rain, snow, or ice), reduced visibility (due to fog[46] or "white out" snow[47]), uneven roads, construction zones,[48] curves,[49] intersections, gravel roads,[50] and heavy traffic.[51] Per distance traveled, consequences of inappropriate speed are more frequent on lower speed, lower quality roads;[52] in the United States, for example, the "speeding fatality rate for local roads is three times that for Interstates".[53]
For speed management, a distinction can exist between excess speed, which consists of driving in excess of the speed limit, and inappropriate speed, which consists of going too fast for the conditions.[54]
Maximum speed limits
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Most countries have a legally assigned numerical maximum speed limit which applies on all roads when no other speed limit indications are present; 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.
The speed limit is commonly set at or below the 85th percentile speed (the operating speed which no more than 15% of traffic exceeds),[55][56][57] and in the US is frequently set 4 to 8 mph (6 to 13 km/h) below that speed.[58] Thus, if the 85th percentile operating speed as measured by a "Traffic and Engineering Survey" exceeds the design speed, legal protection is given to motorists traveling at such speeds (design speed is "based on conservative assumptions about the driver, the vehicle, and roadway characteristics").[59] The theory behind the 85th percentile rules is that, as a policy, most citizens should be deemed reasonable and prudent, and limits must be practical to enforce.[60][61] However, there are some circumstances where motorists do not tend to process all the risks involved, and as a mass, choose a poor 85th percentile speed.[citation needed] This rule, in practice, is a process for "voting the speed limit" by driving, in contrast to delegating the speed limit to an engineering expert.[62][63]
The maximum speed permitted by statute, as posted, is normally based on ideal driving conditions and the basic speed rule always applies.[64] Violation of the statute generally raises a rebuttable presumption of negligence.[65]
On international European roads, speed should be taken into account during the design stage.[citation needed]
Road classification | 60 km/h | 80 km/h (50 mph) | 100 km/h (60 mph) | 120 km/h (75 mph) | 140 km/h (85 mph) |
---|---|---|---|---|---|
Motorway | x | 80 | 100 | 120 | 140 |
Express road | 60 | 80 | 100 | 120 | x |
Road | 60 | 80 | 100 | x | x |
Minimum speed limits
[edit]Some roads also have minimum speed limits, usually where slow speeds can impede traffic flow or be dangerous.[66] The use of minimum speed limits is not as common as maximum speed limits, since the risks of speed are less common at lower speeds.[23] In some jurisdictions, laws requiring a minimum speed are primarily centered around red-light districts or similar areas, where they may colloquially be referred to as kerb crawling laws.[67]
Middle speed limits
[edit]Traffic rules limiting only middle speeds are rare. One such example exists on the ice roads in Estonia, where it is advised to avoid driving at the speed of 25–40 km/h (16–25 mph) as the vehicle may create resonance that may in turn induce the breaking of ice. This means that two sets of speeds are allowed: under 25 km/h (16 mph) and between 40–70 km/h (25–43 mph).[68]
Variable speed limits
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In Germany, the first known experiments with variable speed limit signs took place in 1965 on a 30-kilometre (19 mi) stretch of German motorway, the A8 between Munich and the border city of Salzburg, Austria. Mechanically variable message signs could display speeds of 60, 80 and 100 km/h, as well as text indicating a "danger zone" or "accident". Personnel monitored traffic using video technology and manually controlled the signage.[69] 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 kilometres (810 mi) of German motorways were equipped with such systems.[70]
In the United States, heavily traveled portions of the New Jersey Turnpike began using variable speed limit signs in combination with variable message signs in the late 1960s. Officials can adjust the speed limit according to weather, traffic conditions, and construction.[71] More typically, variable speed limits are used on remote stretches of highway in the United States in areas with extreme changes in driving conditions.[72] For example, variable limits were introduced in October 2010 on a 52-mile (84 km) stretch of Interstate 80 in Wyoming, replacing the winter season speed reduction from 75 to 65 mph (121 to 105 km/h) that had been in place since 2008.[73][74] This Variable Speed Limit system has been proven effective in terms of reducing crash frequency and road closures.[75][76] Similarly, Interstate 90 at Snoqualmie Pass and other mountain passes in Washington State have variable speed limits as to slow traffic in severe winter weather.[72][77] As a response to fog-induced chain-reaction collisions involving 99 vehicles in 1990, a variable speed limit system covering 19 miles (31 km) of Interstate 75 in Tennessee was implemented in fog-prone areas around the Hiwassee River.[78] The Georgia Department of Transportation installed variable speed limits on part of Interstate 285 around Atlanta in 2014. These speeds can be as low as 35 mph (56 km/h) but are generally set to 35 mph (56 km/h).[79] In 2016, the Oregon Department of Transportation installed a variable speed zone on a 30 mi (48 km) stretch of Interstate 84 between Baker City and Ladd Canyon. The new electronic signs collect data regarding temperature, skid resistance, and average motorist speed to determine the most effective speed limit for the area before presenting the limit on the sign. This speed zone was scheduled to be activated November 2016.[citation needed] Ohio established variable speed limits on three highways in 2017, then in 2019 granted the authority to the Ohio Department of Transportation to establish variable limits on any of its highways.[80][81]
In the United Kingdom, a variable speed limit was introduced on part of the 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, and a decrease in the number of crashes; the scheme was made permanent in 1997.[82] However, a 2004 National Audit Organisation 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. Since December 2008 the upgraded section of the M1 between the M25 and Luton has had the capability for variable speed limits.[83] In January 2010 temporary variable speed cameras on the M1 between J25 and J28 were made permanent.[84]
New Zealand introduced variable speed limits in February 2001. The first installation was on the Ngauranga Gorge section of the dual carriageway on State Highway 1, characterized by steep terrain, numerous bends, high traffic volumes, and a higher than average accident rate. The speed limit is normally 80 km/h (50 mph).[85]
Austria undertook a short-term experiment in 2006, with a variable limit configuration that could increase statutory limits under the most favorable conditions, as well as reduce them. In June 2006, a stretch of motorway was configured with variable speed limits that could increase the general Austrian motorway limit of 130 to 160 km/h (81 to 99 mph).[86] 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.[citation needed]
Roads without speed limits
[edit]Just over half of the German autobahns have only an advisory speed limit (a Richtgeschwindigkeit), 15% have temporary speed limits due to weather or traffic conditions, and 33% have permanent speed limits, according to 2008 estimates.[87] The advisory speed limit applies to any road in Germany outside of towns which is either a dual carriageway or features at least two lanes per direction, regardless of its classification (e.g. Autobahn, Federal Highway, State Road, etc.), unless there is a speed limit posted, although it is less common for non-autobahn roads to be unrestricted. All other roads in Germany outside of towns, regardless of classification, do have a general speed limit of 100 km/h (62 mph), which is usually reduced to 80 km/h (50 mph) at Allée-streets (roads bordered by trees or bushes on one or both sites).[88] Travel speeds are not regularly monitored in Germany; however, a 2008 report noted that on the autobahn in Niemegk (between Leipzig and Berlin) "significantly more than 60% of road users exceed 130 km/h (81 mph) [and] more than 30% of motorists exceed 150 km/h (93 mph)".[89] Measurements from the state of Brandenburg in 2006 showed average speeds of 142 km/h (88 mph) on a 6-lane section of autobahn in free-flowing conditions.[90]
Prior to German reunification in 1990, accident reduction programs in eastern German states were primarily focused on restrictive traffic regulation. Within two years of reunification, the availability of high-powered vehicles and a 54% increase in motorized traffic led to a doubling of annual traffic deaths,[91] 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 a decade of effort, while traffic regulations were conformed to western standards (e.g., 130 km/h (81 mph) freeway advisory limit, 100 km/h (62 mph) on other rural roads).[92]
Many rural roads on the Isle of Man have no speed limits;[93] a 2004 proposal to introduce general speed limits of 60 mph (97 km/h) and 70 mph (110 km/h) on Mountain Road, for safety reasons, was not pursued following consultation.[93] Measured travel speeds on the island are relatively low.[94]
The Indian states of Andhra Pradesh,[95] Maharashtra,[96] and Telangana[97] also do not have speed limits by default.
Roads formerly without speed limits
[edit]Many roads without a maximum limit became permanently limited following the 1973 oil crisis. For example, Switzerland and Austria had no maximum restriction prior to 1973 on motorways and rural roads, but imposed a temporary 100 km/h (62 mph) maximum limit in response to higher fuel prices; the limit on motorways was increased to 130 km/h (81 mph) later in 1974.[98][99][100]
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Montana and Nevada were the last remaining U.S. states relying exclusively on the basic rule, without a specific, numeric rural speed limit before the National Maximum Speed Law of 1974.[101] After the repeal of federal speed mandates in 1996, Montana was the only state to revert to the basic rule for daylight rural speed regulation. The Montana Supreme Court ruled that the basic rule was too vague to allow citation, prosecution, and conviction of a driver; concluding enforcement was a violation of the due process requirement of the Montana Constitution.[102] In response, Montana's legislature imposed a 75 mph (121 km/h) limit on rural freeways in 1999.[103]
Australia's Northern Territory had no rural speed limit until 2007, and again from 2014 to 2016. Sections of the Stuart Highway had no limits as part of an open speed limit trial.[104]
Method
[edit]Several methods exist to set up a speed limit:[105]
- Engineering
- Harm minimization
- Economic optimization
- Expert system
For instance, the Injury Minimization (known as Safe System) method takes into account the crash types that are likely to occur, the impact forces that result, and the tolerance of the human body to withstand these forces to set speed limit. This method is used in countries such as the Netherlands and Sweden.[106]
The Operating speed method sets the maximum speed at or around the 85th percentile speed. This reduces the need to enforce the speed limit, but also allows drivers to fail to select the appropriate travel speed, when they misjudge the risk their environment induces. This is one method used in the United States of America.[106]
Enforcement
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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 monitoring, 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.[citation needed]
In 2012, in the UK, 30% of drivers did not comply with speed limits.[23]
In Europe, between 2009 and 2012, 20% of European drivers have been fined for excessive speed.[23] In 2012, in Europe, 62% of people supported the idea of setting up speed-limiting devices,[23] with adequate tolerance levels in order to limit driver confusion. One efficient scheme consists of penalty points and charges for speeding slightly over the speed limit.[23]
Another possibility is to alter the roadway by implementing traffic calming measures, vehicle activated signs, or safety cameras.[107]
The city of Munich has adopted self-explaining roads: roadway widths, intersection controls, and crossing types have been harmonized so that drivers assume the speed limit without a posted sign.[107]
Effectiveness
[edit]Compliance
[edit]Speed limits are more likely to be complied with if drivers have an expectation that the speed limits will be consistently enforced.[108]
To be effective and abided by, the speed limits need to be perceived as credible; they should be reasonable regarding factors such as how well the driver can see ahead and to the sides on a particular road.[23] Speed limits also need to conform to road infrastructure, education, and enforcement activity.[23]
(ONISR, 28 janvier 2019)[109]
In the UK, in 2017, the average free flow speed for each vehicle type is correlated with the applicable speed limit for that road type and for motorways and national speed limit single carriageway roads, the average free flow speed is below the designated speed limit for each vehicle type, except motorcycles on motorways.[110]
Relationship with crash frequency
[edit]A 1998 US Federal Highway Administration report cited a number of studies regarding the effects of reductions in speed limits and the observed changes in speeding, fatalities, injuries and property damage which followed.[111] Some states increase penalties for more serious offenses, by designating as reckless driving, speeds greatly exceeding the maximum limit.[citation needed]
A 2018 OECD-ITF case study established a strong relationship between speed and crash frequency: when the mean speed decreases, the number of crashes and casualties decreases; to the contrary, when speed increases, the number of crashes and casualties increases. In no case was an increase in mean speed associated with a decrease in the number of crashes or casualties.[112]
Source OECD-ITF[112]
Country (year of research publication) | Speed limit reduction | Reported change |
---|---|---|
Australia (1992) | 110 to 100 km/h (68 to 62 mph) | Injury crashes declined by 19% |
Australia (1996) | 5–20 km/h (3.1–12.4 mph) decreases | No significant change (4% increase relative to sites not changed) |
Denmark (1990) | 60 to 50 km/h (37 to 31 mph) | Fatal crashes declined by 24% Injury crashes declined by 9% |
Germany (1994) | 60 to 50 km/h (37 to 31 mph) | Crashes declined by 20% |
Sweden (1990) | 110 to 90 km/h (68 to 56 mph) | Speeds declined by 14 km/h (8.7 mph) Fatal crashes declined by 21% |
Switzerland (1994) | 130 to 120 km/h (81 to 75 mph) | Speeds declined by 5 km/h (3.1 mph) Fatal crashes declined by 12% |
UK (1991) | 60 to 40 mph (97 to 64 km/h) | Speeds declined by 4 mph (6 km/h) Crashes declined by 14% |
US (22 states) (1992) | 5 to 15 mph (8 to 24 km/h) decreases | No significant changes |
NYC, US | 30 to 25 mph (48 to 40 km/h) decreases | 28% reduction in all fatalities and 48 percent reduction in pedestrian fatalities[113] |
Country (year) | Speed limit reduction | Reported change |
France (2018/'19) | Speed reduced from 90 to 80 km/h (56 to 50 mph) (-11%) since July 2018, on 400,000 kilometers of the secondary network covered by 1,000 speed cameras.[114]
Five million euros have been spent on communication to explain the benefits of the speed reduction to 80 km/h (50 mph), using various media, including television, radio, and social media (including 2 million euros for the "13 mètres" advertising movie explaining that speed reduction reduced braking distance by 13 m (43 ft)).[115] |
Effective median speed was reduced from 87.0 km/h (54.1 mph) in June 2018 to 82.6 km/h (51.3 mph) (-5%) in July 2018. Median speed was reduced of 3.9 km/h (2.4 mph) (-4.5%) from 87.0 to 83.2 km/h (54.1 to 51.7 mph) in September 2018.[109]
France to reach its historical best year for road fatalities, stopping a sequence of five years of increasing fatalities:
In 2020, previous results are confirmed for the year 2019: mean car speed was reduced between 2.9 and 3.9 km/h, while mean speed of trucks was reduced by 2 km/h without speed limit change. By the same time, fatalities were reduce by 125 in the second semester 2018, by 84 in the first semester 2019, and 127 for the second semester 2019.[119] However, results were not repeated in overseas territories. Final report considered speed limit change induced a 3.5 km/h (2.2 mph) speed decrease and saved 349 lives during the two years which last 20 months[120] |
Spain (2019) | Decrease speed from 100 to 90 km/h (62 to 56 mph) | In Spain the year 2019 was the best year with the fewest people killed outside a built-up area.
The number of people killed outside built-up areas decreased by 7.6% while the number of people killed on regular roads decreased by 9.5%. The number of people killed in cars outside built-up areas decrease by 16% from 598 to 503.[121] |
Country | Speed limit increase | Reported change |
---|---|---|
Australia (1992) | 100 to 110 km/h (62 to 68 mph) | Injury crashes increased by 25% |
Australia (Victoria) (1996) | 5–20 km/h (3.1–12.4 mph) increases | Crashes increased overall by 8%, 35% decline in zones raised from 60 to 80 km/h (37 to 50 mph) |
Netherlands (2012) | 120 to 130 km/h (75 to 81 mph) | Effect as of yet unclear, more research needed |
US (1989) | 55 to 65 mph (89 to 105 km/h) | Fatal crashes increased by 21% |
US (1990) | 55 to 65 mph (89 to 105 km/h) | Fatal crashes increased by 22% Speeding increased by 48% |
US (40 states) (1990) | 55 to 65 mph (89 to 105 km/h) | Fatalities increased by 15% Decrease or no effect in 12 states |
US (Iowa) (1996) | 55 to 65 mph (89 to 105 km/h) | Fatal crashes increased by 36% |
US (Michigan) (1991) | 55 to 65 mph (89 to 105 km/h) | Fatal and injury crashes increased significantly on rural freeways |
US (Michigan) (1992) | Various | No significant changes |
US (Ohio) (1992) | 55 to 65 mph (89 to 105 km/h) | Injury and property damage increased but not fatal crashes.[122] |
US (40 states) (1994) | 55 to 65 mph (89 to 105 km/h) | Statewide fatality rates decreased 3–5% (Significant in 14 of 40 states) |
US (22 states) (1997) | 5 to 15 mph (8 to 24 km/h) increase | No significant changes |
South Dakota increased its maximum speed limit from 65 to 75 mph (105 to 121 km/h) in 1996. Annual surveys of speed on South Dakota Interstate roads show that from 2000 to 2011, the average speed rose from 71 to 74 mph (114 to 119 km/h).[123] A 1999 study found that the U.S. states that increased speed limits in the wake of the repeal of federally mandated speed limits had a 15% increase in fatalities.[124]
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. The report stated that limited evidence suggests that speed limits have a positive effect on a system wide basis.[n 2]
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 (1.6 km/h) drop in speeds and no discernible reduction in accidents; 20 mph (32 km/h) speed limit zones, which use self-enforcing traffic calming, achieved average speed reductions of 10 mph (16 km/h); child pedestrian accidents were reduced by 70% and child cyclist accidents by 48%.[125] Zones where speeds are set at 30 km/h (or 20 mph) are gaining popularity[126] as they are found to be effective at reducing crashes and increasing community cohesion.[127]
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 found that the measure was effective in reducing speed and the frequency and severity of crashes.[128] 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 (0.3 mph) drop in urban areas and a 0.7 km/h (0.4 mph) drop in rural areas. The report noted that widespread community compliance would require a combination of strategies including traffic calming treatments.[129] Information campaigns are also used by authorities to bolster support for speed limits, for example the "Speeding. No one thinks big of you." campaign in Australia in 2007.
Justification
[edit]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 (e.g. to reduce vehicle emissions or fuel use).[130] Some speed limits have also been initiated to reduce gas-oil imports during the 1973 oil crisis.[131]
Road traffic safety
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According to a 2004 report from the World Health Organization, 22% of all injury mortality worldwide was from road traffic injuries in 2002,[n 3] and without "increased efforts and new initiatives" casualty rates would increase by 65% between 2000 and 2020.[n 4] The report identified that the speed of vehicles was "at the core of the problem",[n 5] and recommended that speed limits be set appropriately for the road function and design, along with the implementation of physical measures related to the road and the vehicle, and increased effective enforcement by the police.[n 6] 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).[132]
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 7] 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 8] when severity is taken into account, the risk is lowest for those traveling at or below the median speed and "increases exponentially for motorists travelling much faster".[n 9]
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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,[133] rising much faster than kinetic energy.[citation needed]
- Kinetic energy
- Braking distance during danger