Editing Speed limit (section)

==Justification==
Speed limits are set primarily to balance [[road traffic safety]] concerns with the effect on travel time and mobility. Speed limits are also sometimes used to reduce consumption of fuel or in response to environmental concerns (e.g. to reduce vehicle emissions or fuel use).<ref name="ec_speed">{{cite web|url=http://ec.europa.eu/transport/road_safety/specialist/knowledge/speed/speed_limits/current_speed_limit_policies.htm|title=Current speed limit policies|publisher=European Commission|quote=A speed limit is based on both safety and mobility considerations and increasingly also on environmental considerations.|access-date=2010-04-23|url-status=dead|archive-url=https://web.archive.org/web/20130125011725/http://ec.europa.eu/transport/road_safety/specialist/knowledge/speed/speed_limits/current_speed_limit_policies.htm|archive-date=2013-01-25}}</ref> Some speed limits have also been initiated to reduce gas-oil imports during the [[1973 oil crisis]].<ref>{{cite web|url=https://www.history.com/this-day-in-history/nixon-signs-national-speed-limit-into-law|title=Nixon signs national speed limit into law|website=history.com|access-date=2019-11-06}}</ref>

===Road traffic safety===
{{See also|Road traffic safety}}
[[File:Ruta Panamericana Buenos Aires Florida.jpg|thumb|The [[Pan-American Highway]] with central median and no freestanding obstructions increasing the level of safety at high speed]]

According to a 2004 report from the [[World Health Organization]], 22% of all injury mortality worldwide was from road traffic injuries in 2002,<ref group="n">{{harvtxt|World Health Organization|2004}} p. 34 fig 2.1</ref> and without "increased efforts and new initiatives" casualty rates would increase by 65% between 2000 and 2020.<ref group="n">{{harvtxt|World Health Organization|2004}} p. 3</ref> The report identified that the speed of vehicles was "at the core of the problem",<ref group="n">{{harvtxt|World Health Organization|2004}} p. 76</ref> 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.<ref group="n">{{harvtxt|World Health Organization|2004}} p. 127</ref> Road incidents are said to be the leading cause of [[Child mortality|deaths among children]] 10–19 years of age (260,000 children die a year; 10 million are injured).<ref name="bbc">{{cite news|url=http://news.bbc.co.uk/2/hi/in_depth/7776127.stm|title=UN raises child accidents alarm|work=BBC News|date=2008-12-10}}</ref>

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.<ref group="n">{{harvtxt|Federal Highway Administration|1998|p=2}}</ref> 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;<ref group="n">{{harvtxt|British Columbia Ministry of Transportation|2003}}, p. v 'The likelihood of a crash occurring is significantly greater for motorists traveling at speed slower and faster than the mean speed of traffic'</ref> 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".<ref group="n">{{harvtxt|Federal Highway Administration|1998|p=2}} 'When the consequences of crashes are taken into account, the risk of being involved in an injury crash is lowest for vehicles that travel near the median speed or slower and increases exponentially for motorists traveling much faster'</ref>

[[File:One-lane chicane 1.jpg|thumb|[[Traffic calming]] can be effective on lower speed roads.]]
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|motor vehicle collision]] is proportional to the square of the speed at [[collision|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,<ref name="tfhrc_1998">{{cite report|url=https://safety.fhwa.dot.gov/speedmgt/ref_mats/fhwasa09028/resources/Synthesis%20of%20Safety%20Researc...pdf|title=Synthesis of Safety Research Related to Speed and Speed Limits|publisher=[[Federal Highway Administration]]|access-date=2009-09-17|year=1998}}</ref> rising much faster than kinetic energy.{{Citation needed|date=June 2019}}

'''Kinetic energy:'''<br />

<math>E_\mathrm{kin} = \frac{1}{2} m v^2</math>

'''Braking distance during danger'''<br />

<math>s_\mathrm{GefahrBrems} \approx \frac{1}{2} \cdot \left( \frac{v^2}{10^2} \right) </math>

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|x=-5,-4,-3,-2,-1,0,1,2,3,4,5
|y1Title=30 mph
|y1=.22,.36,.51,.66,.83,1,1.18,1.38,1.59,1.81,2.04
|y2Title=50 mph
|y2=.48,.58,.68,.79,.89,1,1.11,1.22,1.34,1.46,1.58
|y3Title=80 mph
|y3=.75,.8,.85,.9,.95,1,1.05,1.1,1.16,1.21,1.27
|legend=Expected fatal crash changes by modification in average operated speed
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}}<ref>Source: Reproduced from AASHTO (2010)</ref><ref>{{cite web|url=http://www.onisr.securite-routiere.gouv.fr/sites/default/files/2020-02/Countermeasures%20That%20Work%209%C3%A8me%20%C3%A9dition%202017%20Guide%20Complet%20NHTSA.pdf|title=Countermeasures guide|website=www.onisr.securite-routiere.gouv.fr|access-date=2020-12-29}}{{Dead link|date=January 2021|bot=InternetArchiveBot|fix-attempted=yes}}</ref>

Typically [[motorways]] have higher speed limits than conventional roads because motorways have features which decrease the likelihood of collisions and the severity of impacts. For example, motorways separate opposing traffic and crossing traffic, employ [[traffic barrier]]s, and prohibit the most vulnerable users such as pedestrians and bicyclists. Germany's crash experience illustrates the relative effectiveness of these strategies on crash severity: on autobahns 22 people died per 1,000 injury crashes, a lower rate than the 29 deaths per 1,000 injury accidents on conventional rural roads. However, the rural risk is five times higher than on urban roads; speeds are higher on rural roads and autobahns than urban roads, increasing the severity potential of a crash.<ref name="www.destatis.de 2012"/> The net effect of speed, crash probability, and impact mitigation strategies may be measured by the rate of deaths per billion-travel-kilometres: the autobahn fatality rate is 2 deaths per billion-travel-kilometres, lower than either the 8.7 rates on rural roads or the 5.3 rate in urban areas. The overall national fatality rate was 5.6, slightly higher than urban rate and more than twice that of autobahns.<ref name="http://www.bast.de 2011">{{cite web|title=Traffic and Accident Data: Summary Statistics - Germany|date=December 2012|url=http://www.bast.de/nn_76784/DE/Publikationen/Broschueren/Dokumente/infokarten-national-englisch,templateId=raw,property=publicationFile.pdf/infokarten-national-englisch.pdf|publisher=Bundesanstalt für Straßenwesen [Federal Highway Research Institute]|access-date=2013-09-10|archive-url=https://web.archive.org/web/20130626165800/http://www.bast.de/nn_76784/DE/Publikationen/Broschueren/Dokumente/infokarten-national-englisch,templateId=raw,property=publicationFile.pdf/infokarten-national-englisch.pdf|archive-date=2013-06-26|url-status=dead}}</ref>

The 2009 technical report ''An Analysis of Speeding-Related Crashes:Definitions and the Effects of Road Environments'' by the [[National Highway Traffic Safety Administration]] showed that about 55% of all speeding-related crashes when fatal listed "exceeding posted speed limits" among their crash factors, and 45% had "driving too fast for conditions" among their crash factors. However, the authors of the report did not attempt to determine whether the factors were a crash cause, contributor, or an unrelated factor.<ref>{{cite report|url=http://www-nrd.nhtsa.dot.gov/Pubs/811090.PDF|title=An Analysis of Speeding-Related Crashes:Definitions and the Effects of Road Environments|last1=Liu|first1=Cejun|last2=Chen|first2=Chou-Lin|year=2009|publisher=National Highway Traffic Safety Administration}}</ref> Furthermore, separate research finds that only 1.6% of crashes are ''caused'' by drivers that exceed the posted speed limit.<ref>{{cite web|url=https://www.thenewspaper.com/news/38/3801.asp|title=State Reports Show Speeding Not a Significant Cause of Accidents|website=www.thenewspaper.com}}</ref> Finally, exceeding the posted limit may not be a remarkable factor in the crash analysis as there are roadways where virtually all motorists are in technical violation of the law.<ref>{{cite web|first=Scott|last=Friedman|url=http://www.nbcdfw.com/investigations/Dallas-Freeways-Where-Almost-Everyone-Speeds-138851784.html|title=Nearly Everyone Speeds on Dallas Co. Freeways|website=NBC 5 Dallas-Fort Worth|date=2012-02-07}}</ref>

The speed limit will also take note of the speed at which the road was designed to be driven (the [[design speed]]), which is defined in the US as "a selected speed used to determine the various geometric design features of the roadway".<ref>{{cite report|title=Design Speed, Operating Speed, and Posted Speed Practices|url=http://onlinepubs.trb.org/onlinepubs/nchrp/nchrp_rpt_504.pdf|id=Report 504|publisher=National Cooperative Highway Research Program}}</ref> However, traffic engineers recognize that "operating speeds and even posted speed limits can be higher than design speeds without necessarily compromising safety"<ref>{{cite report|url=http://onlinepubs.trb.org/onlinepubs/nchrp/nchrp_rpt_504.pdf|title=Design Speed, Operating Speed, and Posted Speed Practices|id=Report 504|publisher=National Cooperative Highway Research Program|quote=A significant concern with the 1954 design speed concept was the language of the definition and its relationship with operational speed measures. The term "maximum safe speed" is used in the definition, and it was recognized that operating speeds and even posted speed limits can be higher than design speeds without necessarily compromising safety. In 1997, Fambro et al. (15) recommended a revised definition of design speed for the Green Book while maintaining the five provisions noted above. The definition recommended was, "The design speed is a selected speed used to determine the various geometric design features of the roadway." The term "safe" was removed to avoid the perception that speeds greater than the design speed were "unsafe." The AASHTO Task Force on Geometric Design voted in November 1998 to adopt this definition, and it was included in the 2001 Green Book (17).}}</ref> since design speed is "based on conservative assumptions about driver, vehicle and roadway characteristics".<ref name="tti.tamu.edu" />

[[Vision Zero]], which envision reducing road fatalities and serious injuries to zero by 2020, suggests the following "possible long term maximum travel speeds related to the infrastructure, given best practice in vehicle design and 100% restraint use":<ref>{{cite web|url=http://www.monash.edu.au/muarc/reports/papers/visionzero.html|quote=Table 1. Possible long term maximum travel speeds related to the infrastructure, given best practice in vehicle design and 100% restraint use...|title=Vision Zero - An ethical approach to safety and mobility|author1=Claes Tingvall|author2=Narelle Haworth|name-list-style=amp}}</ref>
{| class="wikitable"
|+Possible maximum travel speeds:
|-
! Type of infrastructure and traffic
! Possible travel speed (km/h)
|-
|Locations with possible conflicts between pedestrians and cars||{{cvt|30|kph}}
|-
|Intersections with possible side impacts between cars||{{cvt|50|kph}}
|-
|Roads with possible frontal impacts between cars, including rural roads<ref>{{cite news|url=http://www.independent.ie/national-news/eu-wants-to-slash-rural-speed-limit-2376195.html|title=EU wants to slash rural speed limit|quote="Europe's top road safety agency warned yesterday that the speed limit on our killer rural roads is too high and should be slashed by a third...The general speed limit of 100 km/h on main rural roads which do not have dividing crash barriers should be cut to 70 km/h or less, an official report recommended yesterday."|access-date=2010-11-10|date=2010-10-13|newspaper=[[Irish Independent]]
}}</ref>||{{cvt|70|kph}}
|-
|Roads with no possibility of a side impact or frontal impact (only impact with the infrastructure)||{{cvt|100|kph}}+
|-
|}"Roads with no possibility of a side impact or frontal impact" are sometimes designated as Type 1 ([[motorways]]/[[freeways]]/[[Autobahns]]), Type 2 ("[[2+2 road]]s"), or Type 3 ("[[2+1 road]]s").<ref>{{cite web|url=http://www.nra.ie/Publications/DownloadableDocumentation/RoadDesignConstruction/file,11236,en.pdf|title=NRA New Divided Road Types: Type 2 and Type 3 Dual-carriageways|publisher=(Ireland) National Road Authority|quote=Type 2 Dual Carriageway: A divided all-purpose road with two lanes in each direction Type 3 Dual Carriageway: A divided all purpose road with two lanes in one direction of travel and one lane in the other direction. the two-lane section, which provides the overtaking opportunity, alternates with a one-lane section at intervals|access-date=2010-11-22|url-status=dead|archive-url=https://web.archive.org/web/20110103164737/http://nra.ie/Publications/DownloadableDocumentation/RoadDesignConstruction/file,11236,en.pdf|archive-date=2011-01-03}}</ref> These roadways have [[Traffic barrier|crash barriers]] separating opposing traffic, [[limited access road|limited access]], [[grade separation]] and prohibitions on slower and more vulnerable road users. Undivided rural roads can be quite dangerous even with speed limits that appear low by comparison. For example, in 2011, Germany's {{cvt|100|kph}}-limited rural roads had a fatality rate of 8.7 deaths per billion travel-km, over four times higher than the autobahn rate of 2 deaths.<ref name="http://www.bast.de 2011" /> Autobahns accounted for 31% of German road travel in 2011,<ref name="http://www.bast.de 2011" /> but just 11% (453 of 4,009) of traffic deaths.

In 2018, an IRTAD WG published a document which recommended maximum speed limits, taking into account forces the human body can tolerate and survive.<ref name="ReferenceA"/>

{| class="wikitable"
|+Towards a safe system, reasonable speed limits (IRTAD WG approach, 2018):
|-
! Type of infrastructure and traffic
! Possible travel speed (km/h)
|-
|Locations (built up areas) with possible conflicts between pedestrians and cars||{{cvt|30|kph}} or {{cvt|40|kph}}
|-
|Intersections with possible side impacts between cars||{{cvt|50|kph}}
|-
|rural roads without median barrier, with risk of head-on collisions||{{cvt|70|kph}} or {{cvt|80|kph}}
|-
| colspan="2" | Source IRTAD, 2018
|-
|}

===Fuel efficiency===
Fuel efficiency sometimes affects speed limit selection. The United States instituted a [[National Maximum Speed Law]] of {{cvt|55|mph}}, as part of the [[Emergency Highway Energy Conservation Act]], in response to the [[1973 oil crisis]] to reduce fuel consumption.<ref name="usdoj1">{{cite web|url=http://www.usdoj.gov/osg/briefs/1989/sg890328.txt|title=Nevada brief in ''Nevada v. Skinner''|url-status=dead|archive-url=https://web.archive.org/web/20101128193331/http://www.justice.gov/osg/briefs/1989/sg890328.txt|archive-date=2010-11-28}}</ref> According to a report published in 1986 by [[The Heritage Foundation]], a [[Conservatism in the United States|Conservative]] advocacy group, the law was widely disregarded by motorists and hardly reduced consumption at all.<ref name="heritage1">{{cite web|title=The High Cost of the 55 MPH Speed Limit|access-date=2007-04-19|last=Copulos|first=Milton R.|url=http://www.heritage.org/Research/SmartGrowth/bg532.cfm|publisher=[[The Heritage Foundation]]|date=1986-09-09|url-status=unfit|archive-url=https://web.archive.org/web/20070510160215/http://www.heritage.org/Research/SmartGrowth/bg532.cfm|archive-date=2007-05-10}}</ref> In 2009, the [[American Trucking Associations]] called for a {{cvt|65|mph}} speed limit, and also national fuel economy standards, claiming that the lower speed limit was not effective at saving fuel.<ref>{{cite web|url=http://www.ens-newswire.com/ens/jan2009/2009-01-27-093.asp|title=Trucking Industry Asks Congress for National 65 mph Speed Limit|date=2009-01-27|publisher=Environment News Service|access-date=2009-02-08|archive-date=2009-01-31|archive-url=https://web.archive.org/web/20090131051033/http://ens-newswire.com/ens/jan2009/2009-01-27-093.asp|url-status=dead}}</ref>

===Environmental considerations===
Speed limits can also be used to improve local air quality issues or other factors affecting [[environmental quality]]<ref name="Int Panis">{{cite journal|vauthors=Int Panis L, etal|year=2011|title=PM, NOX and CO2 emission reductions from speed management policies in Europe|journal=Transport Policy|volume=18|issue=1|pages=32–37|doi=10.1016/j.tranpol.2010.05.005}}</ref> (e.g. the "[[Speed limits in the United States#Environmental speed limits|environmental speed limits]]" in an area of [[Texas]]).<ref>{{cite web|url=http://www.tceq.state.tx.us/implementation/air/sip/speedlimit.html|title=Vehicular Speed-Limit Reduction|work=Texas Commission on Environmental Quality|year=2002|access-date=2010-04-13|url-status=dead|archive-url=https://web.archive.org/web/20100126004805/http://www.tceq.state.tx.us/implementation/air/sip/speedlimit.html|archive-date=2010-01-26}}</ref> The [[European Union]] is also increasingly using speed limits as in response to environmental concerns.<ref name="ec_speed" />
European studies have stated that, whereas the effects of specific speed reduction schemes on particulate emissions from trucks are ambiguous, lower maximums speed for trucks consistently result in lower emissions of [[Carbon dioxide|CO<sub>2</sub>]] and better [[fuel efficiency]].<ref name="Int Panis" />