Speed Limits

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. Speed limits are generally indicated on a traffic sign reflecting the maximum permitted speed - expressed as kilometres per hour (km/h) and/or miles per hour (mph). 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.

The first numeric speed limit for automobiles was the limit introduced in the United Kingdom in 1861.

the highest posted speed limit in the world is , applied on two motorways in the UAE. 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. Additionally, "drivers often drive at high speeds ndunsafe driving practices are common, especially on inter-city highways. On highways, unmarked speed bumps and drifting sand create additional hazards", according to an American-government travel-advisory.

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. As of 2021, the WHO estimates that approximately 1.3 million people die of road traffic crashes each year.

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. Some cities have reduced limits to as little as for both safety and efficiency reasons. However, some research indicates that changes in the speed limit may not always alter average vehicle speed.
Lower speed-limits could reduce the use of over-engineered vehicles.

History

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. 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).

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 on open roads in town, which was reduced to in towns and in rural areas by the 1865 "Red Flag Act." The Locomotives on Highways Act 1896, which raised the speed limit to is celebrated by the annual London to Brighton Veteran Car Run.

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 .

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 in cities and 15 mph on rural roads. Speed limits then propagated across the United States; by 1930 all but 12 states had established numerical limits.

In 1903, in the UK, the national speed limit was raised to ; 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 was imposed in urban centers, and in July 1967, a national speed limit was introduced.

In Australia, during the early 20th century, there were people reported for "furious driving" offenses. One conviction in 1905 cited a vehicle furiously driving when passing a tram traveling at half that speed.

In May 1934, the Nazi-era "Road Traffic Act" imposed the first nationwide speed limit in Germany.

In the 1960s, in continental Europe, some speed limits were established based on the V85 speed, (so that 85% of drivers respect this speed).

In 1974, Australian speed limits underwent metrication: the urban speed limit of was converted to 60 km/h; the rural speed limits of and were changed to and respectively.

In 2010, Sweden defined the '' Vision Zero'' program, a multi-national road traffic safety project that aims to achieve a highway system with no fatalities or serious injuries involving road traffic.

Regulations

Most countries use the metric speed unit of kilometers per hour, while others, including the United States, United Kingdom, and Liberia, use speed limits given in miles per hour. Although there have been discussions about a switch to using metric units in countries' other systems (see Metrication in the United Kingdom and Metrication in the United States), there are currently no proposals to change these laws.

Basic rule

Vienna Convention on Road Traffic

In countries bound by the Vienna Conventions on Road Traffic (1968 & 1977), Article 13 defines a basic rule for speed and distance between vehicles:

Reasonable speed

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.

The German Highway Code (''Straßenverkehrs-Ordnung'') section on speed begins with the statement (translated to English):

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; when the road descends rapidly; when road sections are small, busy, or residential in nature; when approaching the top of a hill; when nearing a crossing where visibility is uncertain; when specific lights are used; or when overtaking animals. If drivers do not master 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, or when drivers encounter sharp corners, a blinding glare, darkness, crossing traffic, 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).

In the United States, this requirement is referred to as the basic rule, as outlined by US federal government law (49 CFR 392.14), which applies in all states as permitted under the commerce clause and due process clause. 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". 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. Citations for violations of the basic speed law without a crash have sometimes been ruled unfairly vague or arbitrary, hence a violation of the due process of law, at least in the State of Montana. Even within states, differing jurisdictions (counties and cities) choose to prosecute similar cases with differing approaches.

Excessive speed

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. 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. 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 or "white out" snow), uneven roads, construction zones, curves, intersections, gravel roads, and heavy traffic. Per distance traveled, consequences of inappropriate speed are more frequent on lower speed, lower quality roads; in the United States, for example, the "speeding fatality rate for local roads is three times that for Interstates".

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.

Maximum speed limits

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 operating speed (being the speed which no more than 15% of traffic exceeds), and in the US is frequently set below that speed. 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"). 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. 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. 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.

The maximum speed permitted by statute, as posted, is normally based on ideal driving conditions and the basic speed rule always applies. Violation of the statute generally raises a rebuttable presumption of negligence.

On international European roads, speed should be taken into account during the design stage.

Minimum speed limits

Some roads also have minimum speed limits, usually where slow speeds can impede traffic flow or be dangerous. 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. 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''.

Middle speed limits

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 and between 40–70 km/h (25–43 mph).

Variable speed limits

In Germany, the first known experiments with variable speed limit signs took place in 1965 on a 30 kilometer 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. 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 kilometers (810 miles) of German motorways were equipped with such systems.

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. More typically, variable speed limits are used on remote stretches of highway in the United States in areas with extreme changes in driving conditions. For example, variable limits were introduced in October 2010 on a stretch of Interstate 80 in Wyoming, replacing the winter season speed reduction from that had been in place since 2008. This Variable Speed Limit system has been proven effective in terms of reducing crash frequency and road closures. 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. As a response to fog-induced chain-reaction collisions involving 99 vehicles in 1990, a variable speed limit system covering of Interstate 75 in Tennessee was implemented in fog-prone areas around the Hiwassee River. 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 but are generally set to . In 2016, the Oregon Department of Transportation installed a variable speed zone on a 30-mile 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. Ohio established variable speed limits on three highways in 2017, then in 2019 granted the authority to the Ohio Department of Transportation