Speed limit

For a discussion of the maximum speed possible in the universe, see speed of light and special relativity.

A road speed limit is the maximum speed as allowed by law for road vehicles. Speed limits are commonly set and enforced by the legislative bodies of nations or provincial governments, such as countries within the world.

In addition to setting an explicit maximum speed limit, most governments also enforce speed limits that are related to driving conditions; for example, requiring drivers to adjust their speed when driving in fog or heavy rain. California Civil Code 22350 is typical; it states that "No person shall drive a vehicle upon a highway at a speed greater than is reasonable... and in no event at a speed which endangers the safety of persons or property." This "basic rule", or similar legal language, applies even where no maximum speed limit is in place (such as formerly in the U.S. 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 10mph (16.1km/h) 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 (6 km/h) in the country and 2 mph (3 km/h) in towns. The 1865 Act required a man with a red flag or lantern to walk 60 yards (50 m) 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 (23 km/h) has been commemorated each year since 1927 by the London to Brighton Veteran Car Run.

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. In Germany, 57% of the autobahn motorway system remain free from speed limits. The highest posted speed limit in the world is 160 km/h (99 mph), which was experimentally applied during 2007 on selected test stretches in Austria and the United Arab Emirates.

Factors in setting speed limits

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.

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).

Fuel efficiency also affects the choice of speed limits. The United States at one time had attempted a maximum speed limit of 55 mph (89 km/h) to reduce fuel consumption (See National Maximum Speed Law).

It is also estimated that speed limits can be used to reduce emissions and pollution, and some areas have reduced speed limits for improving the air quality (See Environmental Speed Limits).

Design speed

Main article: Design speed

Definition

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."

Limitations

Safe operating speeds can exceed the design speed. Example reasons include:

1. A design speed is not a representative speed of an entire roadway. Rather, the road's design speed is limited by its most restrictive feature, such as a curve, bottleneck, or hill.
2. Actual roadway design may exceed the design specifications.
3. Current parameters for determining the design speed assumes the capacity of outdated automotive technology.
4. The stated design speed for a given road is usually not changed. Therefore, the design speed on older roads, which were calculated with older methodologies, may not factor in improved automotive technology which can maintain designed safety at higher travel speeds.

In commonly accepted engineering practice, design speed is considered a "first guess" at an appropriate speed limit.

85th percentile rule

In the United States, traffic engineers may rely on the 85th percentile rule 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:

• Political or bureaucratic resistance to higher limits.
• Statutes that restrict jurisdictions from posting limits higher than an arbitrary number.

Signage

For more information about traffic signs in general, see Traffic sign.

Speed limit sign common to much of Europe, showing a 60 km/h (60 mph in the UK) restriction

File:Natspeedlimit.jpg

An Example of a UK National speed limit roadsign.

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 immediately 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 U.S. has shown no intention to convert to SI units, and reverted to imperial units in states that had both imperial and SI systems such as California and Arizona. However, Ohio, South Dakota, Maine, and Vermont (especially near the Canadian border) still have some SI distances and speeds on their exit distance and speed limit signs (such as 70 mph (110 km/h) / 110 km/h, or 3 miles / 5 km to next exit). When entering Canada, signs are posted reminding drivers that metric signage is in use. Conversely upon entering the US from Canada (at least in Vermont), drivers are shown a 100 km/h speed limit sign. All exit distance signs on Interstates in New Hampshire are marked with the distance in miles followed by the distance in kilometres shown in parentheses. Houston, Texas has some signs in both imperial and SI units near its airports and downtown. Delaware Route 1 and Interstate 19 have exits numbered by kilometer - I-19 also has kilometer posts.

Design of speed limit signage varies between countries. In much of Europe the red circle is most common, while in North America, and in Australia, signs are usually rectangular. 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.

• 
  Informational sign at German border crossings.
• 
  Informational sign at Polish border crossings.
• 
  Zonal restriction, common in residential areas
• 
  End of restricted zone
• 
  Two contradictory United States speed limit signs

Speed limits in specific countries

The following table shows the default speed limits that apply in various countries (excepting the local 30 km/h or lower limits in many countries) in km/h (except mph which is posted in the United Kingdom and the United States with those numbers in parentheses):

Country	Within Towns	Automobiles & Motorcycles		Trucks or Automobiles with Trailer
		Outside built-up areas/Expressways	Motorways	Outside built-up areas/Expressways	Motorways
Åland (Finland)	50	70-90
Argentina	40-60	80-110	100-130	80	80
Australia 15	50-60	100-130 (Previously Unlimited) 15	100-110	90-100	90-100
Austria	50	100	13014	1004	1005
Belgium	50	90	120	60-90	90
Brazil	40-70	80-110	No Speed Limit	80 (90 for buses)	80-100
Bulgaria	50	90 ( 80)	130 ( 100)	90	100
Canada	40-60	70-110	100-11016	80-100	100-110
China	40-60	60-80	100-120	N/A	N/A
Croatia	50	90-110	130	80	80
Cyprus	50	80	100	80	100
Czech Republic	50	90-130	130	80	80
Denmark	50	80	110-130	70 (80 for buses)	70
Estonia	50	90-110		90	90
Faroe Islands	50	80
Finland	40-50	80-1006	1206	80	80
France	50	90-110	130	90-110	130
Germany	50	100	no speed limit1	60(trucks)80	80-1007
Gibraltar	30-50
Greece	50	90 ( 70)	130 ( 90)	80 (School buses 60)	80 (School buses 60)
Greenland	50	80
Hong Kong	50	50-70	70-110	50	70
Hungary	50	90-110	130	70	80
India	50	100	80	65	40
Indonesia	30-60	60-80	80-140	60-80	80-100
Iceland12	50	90	90	80	80
Ireland	30-50	80-10011	120	80-100	80
Israel	50	80-90	110	80	90
Italy	50	90-110²	130 ³	70	80
Japan	40-60	50-60	60-100	50-60	80
Korea, South	30-80	60-80	80-120	40-60	80
Latvia	50	90	90	80	80
Liechtenstein	50	80		80
Lithuania	50	70-90	110-130	70-80-90	90
Luxembourg	50	90	130	90	90
Malaysia	40-60	70-9018	110	70-80	80-90
Malta	35-50	70-80		60
Mexico	30-70	80-11017	100-110	95
Netherlands	50	80-100	80-120	80	80
New Zealand	50	100	100	90	90
Norway	50	80-90	90-1009	80	80
Peru	50	60-100	No Speed Limit	70-80	No Speed Limit
Philippines	80	80-120		80-120
Poland	50/6013	90-11013	130	70	80
Portugal	50	90-100	120	70-80	100
Romania	60	90-100	130	80	100
Russia	60	90-110	110	70-90	90
Serbia	60	80-100	120
Singapore	50	80-90	90	60	60
Slovakia	60	90-130	130	80	80
Slovenia	50	90-100	130	80	80
South Africa	60	80-100	120	80-100	80-100
Spain	50	90-100	120	70-80	80
Sweden	30-50	70-110	110-120	80	80
Switzerland	50	80-100	120	80	80
Taiwan	40-60	50-80	100-110	60-80	80-90
Turkey	50	90 ( 70)	120 ( 80)	80	90
United Kingdom10	48 (30 mph)	97-113 (60-70 mph)	113 (70 mph)	64-97 (40-60 mph)21	97 (60 mph)21
Venezuela	50	80-120	No Speed Limit	40-60	60-120
United States10	24-72 (15-45 mph)	89-121 (55-75 mph)	89-129 (55-80 mph)19	Restrictions only in some states, typically 5-15 mph lower.20

|-

^*Motor routes: roads with two or more lanes (dual carriageway), a median, and a minimum speed of 60 km/h.

Remarks:

¹ 130 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.
² On expressway where is indicated.
³ Two and three-lane expressways: 130 km/h; since 2003 on some three-lane expressway a 150 km/h limit was introduced, but is not operative).
⁴ Cars with heavy trailer: 80 km/h; lorries with heavy trailer: 70 km/h.
⁵ Cars with heavy trailer: 100 km/h; lorries with heavy trailer: 80 km/h.
⁶ During winter, when conditions are often bad, all Finnish motorways have a speed limit of 100 km/h or less. Also most roads with 100 km/h speed limit in summer have 80 km/h limit during winter.
⁷ Additional trailer checkup (TÜV) and special speed plaque required on vehicle.
⁹ A provisional increase of the speed limit on motorways from 90 to 100 km/h was made permanent when the number of accidents decreased.
¹⁰ Signs are posted in mph, a situation unlikely to change in the near future.
¹¹ 100 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.
¹² Iceland does not have expressways/motorways in the traditional sense. There is 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.
¹³ 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.
¹⁴ A provisional increase to 160 km/h was in place on a 12 km stretch on the A10 in May and June 2006.
¹⁵ 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 Speed limits in Australia for details.
¹⁶ Speed limit is 110 km/h in several provinces, 100 km/h in others.
¹⁷ Some 2 lane Federal highways are posted at 110 km/h provided they have a paved shoulder.
¹⁸ 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.
¹⁹ The state of Hawaii posts a 55 mph (89 km/h) speed limit on many Interstate highways.
²⁰ Some states require vehicles towing trailers to follow the posted truck speed limit.
²¹ Generally in the UK, lorries over a laden weight of 7500kg are speed-limited to 56 mph (90 km/h). Some lorries or trucks between a laden weight of 3500kg and 7500kg are also speed-limited to 56 mph (90km/h)

Europe

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.

France

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 and the Gendarmerie. The French authorities have credited this increase in traffic enforcement with a 50% drop in road fatalities from 2002 to 2006 (except on Motorways, where the fatalities rose by 15% between 2002 and 2006).

Germany

German autobahns are famous for having no universal motorway speed limit, although about 30% of them have posted speed limits and about 10% are equipped with motorway control systems that can show variable speed limits. There is no national speed limit, either, for cars on marked "Schnellstraßen" (Express-roads) with a central reservation or a minimum of two marked lanes per direction. On such roads, as well as motorways, a recommended speed limit (Richtgeschwindigkeit) of 130 km/h (80 mph) applies. While driving at higher speeds is not punishable, the increased risk induced by higher speeds (erhöhte Betriebsgefahr) may result in partial liability for damages. Moreover, the law forbids to travel at speeds that would prolong the vehicle's minimum halting distance beyond the driver's line of sight. On all German roads, there are speed limits for trucks, buses, cars towing trailers, and small motorised vehicles (Mopeds, etc.).

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.

In 1973, in the wake of the oil crisis, a federal speed limit of 100 km/h on Autobahns was imposed to help conserve fuel for fear of impending future shortages (not for environmental or safety reasons). The measure only lasted from December 1973 to March 1974; while the administration and the Bundestag were in favor of keeping the speed limit, the Bundesrat pushed to repeal the law. As a compromise, a recommended speed was introduced on Autobahns as well as "highways outside of built-up areas with a center divide or without a center divide and a continuous lane for overtaking in both directions". This law is basically still in effect today. Unrestricted non-Autobahn highways, however, have since become virtually non-existent or replaced by Schnellstraßen, Autobahn-like expressways with a limit of up to 120 km/h and normally only covering a few kilometers.

The Umweltbundesamt (Federal Environmental Agency) repeated its recommendation of such regulation in early 2007, but the current Merkel administration sees no need for it. Even after a 2007 party congress held by the SPD, one of Germany's governing parties, where a proposal to impose a blanket speed limit was approved, there was outspoken opposition within the administration. At present, it is generally thought that a blanket speed limit would not be significantly beneficial, regarding both environmental and climate concerns and road safety. Current estimates conclude that a speed limit would reduce Germany's overall CO2 emission by a mere fraction of a percent, and in terms of highway safety, German Autobahns are among the world's safest.

Legally, however, state and even local authorities have the power to enact speed limits. A statewide binding speed limit of 130 km/h, for example, was established in Rhineland-Palatinate over a decade ago, whereas the district of Cologne has posted a speed limit on the heavily frequented Cologne Beltway. Effective April 9, 2008, Bremen (Germany's northernmost city-state) began enforcing a general 120 kilometers per hour speed limit, citing environmental concerns. However, Bremen's new limit only impacted an additional 11 kilometers of Bremen's 60 kilometers of highway ; most Bremen autobahn already had some speed restriction due to congestion and noise.

On rural roads that are neither motorways nor 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, which are marked by distinctive rectangular yellow signs showing the name of the city, 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). Motorways crossing cities count as normal Autobahns and can be used for travel within larger cities in many cases.

Minimum speeds are very rarely marked in Germany. Vehicles which cannot sustain speeds of 60 km/h are not allowed on the Autobahn, however.

In 2006, 57% of the German motorways had no speed limit at all. Roughly one third of regulated roads have computer-controlled traffic guiding systems with variable electronic signs along carriageways showing the set speed limit, or, current road conditions and traffic density allowing, indicating that no speed limit is set at the moment.

Ireland

Main article: Road speed limits in the Republic of Ireland

In the Republic of Ireland, since 2005, the speed limit of motorways has been 120 km/h. 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. Other National primary and national secondary roads have a speed limit of 100 km/h, while regional roads have a limit of 80 km/h. Again, this 80 km/h can be increased due to local by-laws. The limit on built-up areas is generally 50 km/h, but may be increased to 60 km/h or, rarely, reduced to 30 km/h. The conversion of limits to km/h from mph was effected by the 2004 Road Traffic Act. The conversion of speed limit signposts to km/h occurred on 19 January 2005.

Italy

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.

Netherlands

The default speed limit for Dutch motorways (snelwegen) is 120 km/h (75 mph), although many have limits of 100 km/h (62 mph). Regional roads have a limit of 80 km/h (50 mph) and 100 km/h (62 mph) on expressways (autowegen). The limit in built-up areas is 50 km/h (31 mph), but also 70 km/h (44 mph) and 30 km/h (19 mph).

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.

Denmark

Denmark has three general speed limits:

• 50 km/h within towns
• 80 km/h outside towns
• 130 km/h on motorways

The general speed limits for driving with trailers are:

• 50 km/h within towns
• 70 km/h outside towns
• 80 km/h on motorways

Some areas may have lower or higher speed limits. Also the general speed limits apply only for vehicles below 3,5 metric tons. Lower speed limits apply for larger vehicles.

Norway

Norway has two general speed limits, 50 km/h in dense populated areas, and 80 km/h in sparsely populated areas. On some roads the speed limit is 90 km/h. On some of the best motorways around the capital, Oslo, the limit is 100 km/h. They are now working with testroads to raise the maximum speedlimit to 110 km/h.

Sweden

Sweden has the official limits 50 km/h in built-up areas, 70 km/h outside and 110 km/h on motorways. There is also a test road in the south of Sweden with a speed limit of 120 km/h. 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. Outside schools and hospitals the limit is often 30 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.

Finland

• Motorways 120 km/h (in winter or bad weather, as well as on motorways close to urban areas, 100 km/h).
• Main provincial roads (paved) 100 km/h or 80 km/h (on locations or on winter lower).
• Rural roads 80 km/h (paved or gravel) unless otherwise indicated.
• Within a built-up area 50 km/h unless otherwise indicated.

Switzerland

Swiss motorways Autobahnen are limited to 120 km/h (75 mph) and semi-motorways Autostrassen are limited to 100 km/h. Other highways are limited to 80 km/h. The limit in built-up areas is 50 km/h (31 mph).

United Kingdom

UK speed limit upon entry to village, Fivemiletown in Northern Ireland (30 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, and made permanent in 1967 for motorways and dual carriageways with a central reservation (with the limit dropped to 60 mph (100 km/h) 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 The Automobile Association have called for the limit to be increased.

The Road Traffic Act 1930 imposed a speed limit of 20 mph on all heavy goods vehicles on all roads. This was raised to 30 mph in the 1950s.

North America

Speed Limit 80 mph (130 km/h) sign on a rural stretch of Interstate highway in western Texas. It is the highest posted speed limit in the U.S.

United States

Further information: Speed limits in the United States

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:

• 15–30 mph (24–48 km/h) on residential streets
• 35–45 mph (56–72 km/h) on urban arterial roads
• 50–65 mph (80–105 km/h) on major highways inside cities
• 45–65 mph (72–105 km/h) on rural two-lane roads
• 55–70 mph (88–112 km/h) on rural expressways
• 65–80 mph (105–129 km/h) on rural Interstate highways

Speed policy is determined by each state.

Canada

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:

• 30–50 km/h (20–30 mph) within school and playground zones
• 40–50 km/h (25–30 mph) on residential streets within cities and towns
• 60–70 km/h (35–45 mph) on major arterial roads in urban and suburban areas
• 70–90 km/h (50–55 mph) on highways outside cities and towns and urban expressways
• 90–110 km/h (55–70mph) on freeways and rural expressways

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 Prince Edward Island and 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. 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.

In Ontario speeding fines double in areas identified as "Community Safety Zones" as well as "school zones".

Asia

China

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 take some time.

Semi-expressways and city express routes (called kuàisù gōnglù (Chinese: 快速公路) 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 some localities, speed limits may drop to 40 km/h (25 mph).

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" (Chinese: 超速摄像).

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 thwart it).

Hong Kong

Many expressways in Hong Kong are limited to 80 km/h. Some expressways with heavy traffic are limited to 70 km/h, such as Island Eastern Corridor and East Kowloon Corridor. Tolo Highway and West Kowloon Highway have a 100 km/h limit, and North Lantau Highway limited at 110 km/h, the highest speed limit in Hong Kong.

It is important to note that a speeding offence of anything under 10 km/h over the speed limit is not usually enforced - many drivers in Hong Kong travel within this range.

India

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.

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. 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 design speed of 180 km/h.

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.

however the issue over speed limits remains under dispute usually due to political factors.

Indonesia

Indonesia employs 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 guidelines.

Japan

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:

• having no separate urban limit, with urban limits being set by zoning rather than statute.
• emergency vehicles are not exempt but have a higher speed limit,80km.
• there are many lower limits set for vehicle classes other than ordinary cars and motorcycles.
• power output of Japanese domestic cars was governed by a gentlemen's agreement stating that the maximum power output would be 280 PS (276 bhp / 206 kW). This is no longer in place and cars with stated power outputs of more than 280 PS are available.

Korea, South

The speed limit on most city streets and rural two-lane roads is 60-80 km/h, while the limit on expressways managed by the Korea Expressway Corporation ranges between 100 km/h and 120 km/h. Four-lane roads between cities generally have an 80 km/h limit.

Speed limits are strictly enforced by Highway Patrols and by way of various radar devices such as speed guns, safety cameras, speed cameras and other vehicle-monitoring devices.

Malaysia

Malaysian National Speed Limit signboard.

Further information: National Speed Limits

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.

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.

Pakistan

In Pakistan, on newly constructed motorways, M2 and M1, speed limit is 120 km/h. Most residential areas of big cities, the speed limit is 40 km/h. Major roads of cities have 80 km/h of speed limit.

Philippines

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.

Singapore

The speed limit of Singapore highways/expressways is 90 km/h.

Taiwan

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:

• 15 km/h when approaching a railroad crossing
• 40 km/h on roads without lane markings or on slow lanes (Chinese: 慢車道) separated by single solid white lines from nearby fast lanes (Chinese: 快車道)
• 50 km/h on other roads and lanes

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.

Oceania

Australia

Australian speed limit sign

Further information: Speed limits in Australia

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:

• within built-up areas, 50 km/h. (60 km/h in the Northern Territory)
• outside built-up areas, 100 km/h. Western Australia and South Australia has a limit of 110 km/h, and the Northern Territory is limited to 110 km/h or 130 km/h on selected roads.

New Zealand

Speed limits in New Zealand range up to and including 100 km/h. The most commonly seen are:

• 100 km/h, the current open road limit. Used in rural areas, and on motorways, expressways and highways, as well as areas where there is little development on the roadside.
• 80 km/h is used where it would not be safe to use the 100 km/h open road limit, such as urban arterial routes or areas requiring extra care (such as Auckland City's Central Motorway Junction, due to its complexity.). Before 1986, 80 km/h was the open road limit.
• 70 km/h in small country towns, urban fringes (often preceding a change from the open limit to urban limit), or where development is only on one side of the road
• 50 km/h in most urban or built-up areas; LSZ (see below) under adverse conditions
• 30 km/h through most roadworks.
• 20 km/h traffic traveling both ways past school buses that have stopped to unload or pick up passengers; and through accident sites

Some vehicles are restricted to lower overall speed limits such as trucks and vehicles with trailers (90km/h), and school buses displaying signs (80 km/h)

Signage tends to follow the European model of a number inside a red circle. Sometimes the 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 is progressively being replaced.

There is no minimum speed limit but vehicles traveling less than the maximum must keep to the side of the road and pull over to allow others to pass as soon as is safe.

Africa

Namibia

The general speed limits in Namibia are (according to Road Authority of Namibia):

• 60 km/h on a public road within an urban area (may be lifted to 80 km/h on some major urban roads)
• 120 km/h on every tarmac freeway.
• 80-120 km/h on non-tarmac freeway ("gravel" road)

South Africa

The general speed limits in terms of the South African National Road Traffic Act, 1989 and its regulations are:

• 60 km/h on a public road within an urban area
• 100 km/h on public road outside an urban area which is not a freeway; and
• 120 km/h on freeways.

Tunisia

The general speed limits in Tunisia are:

• 50 km/h on public roads within an urban area
• 90 km/h on public roads outside an urban area which is not a freeway; and
• 110 km/h on freeways.

Enforcement

Further information: [[:Road safety camera]]

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, aircraft, 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.

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. 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[.]"

Enforcement tolerance

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 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.

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 (20 km/h) over a speed limit of less than 55 mph (89 km/h) or for traveling less than 6 mph (10 km/h) over a speed limit of 55 mph (89 km/h) or greater.

In Taiwan, even though the Regulations on Establishing Traffic Signs and Indicating Lines (zh:道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, effective 00:00 (UTC+8) on September 16, 2006, a tolerance of 10 km/h has been allowed as on other Taiwanese roads.

In Hong Kong, there is a tolerance of 10 km/h over the posted speed limit.

In the United Kingdom ACPO guidelines recommend a tolerance level of the speed limit "+10% +2 mph" (e.g. a tolerance level in a 30 mph (50 km/h) zone of 35 mph). However, each police force or safety camera partnership has the ability to use its discretion when setting the levels at which drivers will be prosecuted.

In the Netherlands drivers can get a fine for driving 4 km/h over the speed limit, after applying a 3 or 4 km/h correction factor to compensate for measuring errors. Police officers are usually not allowed to use their discretion when setting the speeding threshold during enforcement activities by photo radar.

Road safety improvements in the Australian state of Victoria are largely attributed 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 which cites:

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.

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 only stipulate that a car's speedometer must be accurate within a 10% tolerance.

In Germany, traveling at any speed above the posted speed limit constitutes a speeding offense. A 3 km/h tolerance in favor of the offender, however, is always deducted. Fines for speeding depend on how high above the speed limit the measured speed is, and on where the offense occurred. Speeding in built-up areas invariably carries higher fines than outside city limits. While fines for minor offenses tend to be moderate, speeds in excess of 20 km/h above the limit in built-up areas and 30 km/h on other roads not only result in distinctly higher fines, but also points on the driver's license, and, again depending on the speed at which the offender was clocked, may lead to a driving ban of at least one month.

Evading Enforcement

Methods for evading enforcement of speed limits have entered popular culture. Among the most familiar techniques is to purchase a radar detector to seek out police radar signals before one enters an enforcement zone. Observers have pointed out a small-scale arms race ensues, as speeders buy radar detectors of greater technology and police purchase equipment that is harder to detect. Such detectors are illegal in certain jurisdictions. Speeders can also alter their traffic behavior according to known police stake-out positions.

Database of Speed Limits

Databases are available containing the GPS location of speed limit signs. One is the Open-Speedlimit-Database. This information can be used to build advance cruise controls, eventually leading to the driverless car.

Safety and efficacy

Essential physics

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, 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.

Speed limits, actual speeds, and aggregate safety

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." 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."

A 1994 study by Jeremy Jackson and Roger Blackman showed, consistent with the risk homeostasis theory, that although increased speed limits and reduced speeding fines significantly increased driving speed, there was no effect on accident frequency, with the 24 participants maintaining the same level of risk and risky behaviour. It also showed that an increased accident cost caused large and significant reductions in accident frequency but no change in speed choice. The abstract states that the results suggest that regulation of specific risky behaviors such as speed choice may have little influence on accident rates.

Speed and crash factors

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 (50 km/h); for example, truck rollovers on exit ramps.

Variable speed limits

Example variable speed limit sign in the United States.

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 indicated savings in journey times, smoother-flowing traffic, and a fall in the number of accidents, so the implementation was made permanent in 1997. Further trials on the M25 have been thus far proved inconclusive.

In Germany, the first experiments with variable signs took place in 1965 on A8 Munich-Salzburg with signs that were operated manually. 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.

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. The electronic signage is commonly posted every 500 metres. The system keeps track of all traffic movement and lowers the speed limit if it detects the start of traffic congestion. When activated the speed limit 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. Variable speed limit signs, in combination with variable message signs, have been in use since the 1960s on the New Jersey Turnpike, where officials can adjust the speed limit according to weather, traffic conditions, and construction. Other roadways with variable speed limits include the Pulaski Skyway in New Jersey and I-495 in Delaware.

Opposition

Speed limits and their enforcement have been opposed by some motorists since their inception. Britain's first motoring organisation, 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:

• Inconclusive results from most speed limit studies. For example, a 1972 OECD Road Research Group report entitled 'Speed Limits Outside Built-Up Areas' reviewed most international studies to that date. They concluded that "because of the weaknesses in the research designs of many investigations, scientifically well-established conclusions cannot be drawn." "Indeed, some of the speed limit changes were more in the nature of administrative exercises than scientifically designed experiments and the methods of analysis in these cases were deficient from the statistical point of view." The Group stated that "speed limit policies should be based on reliable research work and generally accepted scientific evidence." They proposed an international co-operative experiment to overcome weaknesses in prior studies. However, the 1973-1974 oil price crisis intervened, and widespread blanket speed limits became more common without exacting study. More recently, a review of the effect of speed on vehicle crash rates noted that the studies and evidence are "ample, but not unequivocal."
• Misleading definition of 'speeding' or 'speed-related' to combine the concepts of:
  • crashes that occur often at relatively low speeds, but excessive for adverse conditions, such as low visibility
  • citations that are issued for travel in excess of the posted speed limit

In Australia for instance, Government & Police attribute speed as the main cause in 30% of crashes, even though speeding is a cause in only 20% of those cases (or 6% of total cases). This is due to an extremely wide-ranging definition of speed, in order to explain fixed speed cameras and zero-discretion traffic policing.

• Surprisingly broad range for 'speed-related' fatalities as a percentage of total traffic fatalties, suggesting that categorizing accidents as 'speed-related' is highly subjective. Among the U.S. States, the range is from 10% in New Jersey to over 60% in Rhode Island.
• "Evidence that suggests the net effect of [higher motorway] speed limits may be positive on a system wide basis [by shifting more traffic to these safer roads]." This statement from 1998 U.S. Federal Synthesis is based on the published, peer-reviewed work of Charles A. Lave et al., e.g. "Did the 65 mph Speed Limit Save Lives?"
• Motorists generally pick reasonable speeds for conditions, even on motorways. For example, the 75 mph (120 km/h) speed limit in the U.S. State of South Dakota has good compliance: the average speed is less than or equal to the posted limit almost a decade after it was increased.

• "When speed limits are set artificially low, tailgating, weaving and speed variance (the problem of some cars traveling significantly faster than others) make roads less safe"

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 62 mph (100 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.

Finally, opposition to speed limits exists purely on the philosophical level. Some question the institution of enforcing speed limits (among other motor vehicle offenses) are criminalizing a hitherto unknown percentage of the population. Prior to the enforcement of speed limits, perhaps only a small percentage of individuals would find themselves outside the law. After the creation of motor vehicle legislation, the average individual is quite likely to break the law at some point in their driving career.

Roads without speed limits

In some jurisdictions some public roads have no speed limits:

• The German intercity Autobahn, two-thirds of which have only advisory limits (Richtgeschwindigkeit).

• The Isle of Man has no speed limit on many rural roads. A 2004 proposal for 70 and 60 mph (112 and 96 km/h) speed limits was very unpopular., although measured travel speeds are often low.
• Nepal has average traffic speeds of 40-50 km/h and has no statutory speed limits set on most of its roads.
• The state of Uttar Pradesh in India has no default speed limit for cars. (see India Speed Limit)

Montana has had a speed limit since June 1999 (see Montana Speed Limit). Australia's Northern Territory had no blanket speed limits outside major towns until January 2007, when rural speed limits were reduced to 110 km/h or 130 km/h [3].

See also

• Road-traffic safety
• Speed trap
• Road-rule enforcement camera
• Traffic Violations Reciprocity
• Operating speed
• Design speed

External links

• Governments
  • Transport, Local Government and the Regions - Ninth Report A comprehensive UK report into the effects of speeding.
  • The Speeding Driver: Who, How and Why? A major research report into the psychology of the speeding driver.
• Motorists' and other groups
  • National Motorists Association A U.S. organization arguing for 85th percentile limits.
  • Slower Speeds Initiative A UK road safety organisation which campaigns for lower speed limits.
  • Higher/Flexible Speeds Initiative An Austrian project that aim at more flexible speed limits and also higher speed limits for a better traffic control and safer driving.
• Other links
  • Alert and Find Speed Traps In Your Area pigradar.com
  • John F. Carr's State Traffic and Speed Laws
  • R.A. Krammes, K. Fitzpatrick, J.D. Blaschke, D.B. Fambro. Speed: Understanding Design, Operating, and Posted Speed, Research Report 1465-1. Project No. 1465. Texas Transportation Institute, College Station, TX. March 1996.
  • The United States' Transportation Research Board (TRB) National Cooperative Highway Research Program (NCHRP): Report 504: Design Speed, Operating Speed, and Posted Speed Practices 2003.
  • C. Lave and P. Elias, "Did The 65 MPH speed Limit Save Lives?" Accident Analysis and Prevention, Vol. 26, No. 1, 1994.
  • Effects of Raising and Lowering Speed Limits on Selected Roadway Sections, United States Publication No. FHWA-RD-97-084, January 1997.
  • Actual Speeds on the Roads Compared to the Posted Limits, Final Report 551, Arizona Dept of Transportation, October 2004.
  • Special Report 254: Managing Speed, Transportation Research Board, 1998.
  • The Flicker Fusion Factor Why we can't drive safely at high speed
  • Speed control devices for vehicles Technology is being developed to assist drivers keep to the speed limits.