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) or miles per hour (mph) or both. Speed limits are commonly set by the legislative bodies of national or provincial governments and enforced by national or regional police and judicial authorities. Speed limits may also be variable, or in some places nonexistent, such as on most of the Autobahnen in Germany.
Traffic calming uses physical design and other measures to improve safety for motorists, car drivers, pedestrians and cyclists. It has become a tool to combat speeding and other unsafe behaviours of drivers. It aims to encourage safer, more responsible driving and potentially reduce traffic flow. Urban planners and traffic engineers have many strategies for traffic calming, including narrowed roads and speed humps. Such measures are common in Australia and Europe, but less so in North America. Traffic calming is a calque of the German word Verkehrsberuhigung – the term's first published use in English was in 1985 by Carmen Hass-Klau.
Level of service (LOS) is a qualitative measure used to relate the quality of motor vehicle traffic service. LOS is used to analyze roadways and intersections by categorizing traffic flow and assigning quality levels of traffic based on performance measure like vehicle speed, density, congestion, etc. In a more general sense, levels of service can apply to all services in asset management domain.
Traffic signs or road signs are signs erected at the side of or above roads to give instructions or provide information to road users. The earliest signs were simple wooden or stone milestones. Later, signs with directional arms were introduced, for example the fingerposts in the United Kingdom and their wooden counterparts in Saxony.
Road traffic safety refers to the methods and measures, such as traffic calming, to prevent road users from being killed or seriously injured. Typical road users include pedestrians, cyclists, motorists, passengers of vehicles, and passengers of on-road public transport, mainly buses and trams.
A variable-message sign or message board, often abbreviated VMS, VMB, CMS, or DMS, and in the UK known as a matrix sign, is an electronic traffic sign often used on roadways to give travelers information about special events. Such signs warn of traffic congestion, accidents, incidents such as terrorist attacks, AMBER/Silver/Blue Alerts, roadwork zones, or speed limits on a specific highway segment. In urban areas, VMS are used within parking guidance and information systems to guide drivers to available car parking spaces. They may also ask vehicles to take alternative routes, limit travel speed, warn of duration and location of the incidents, inform of the traffic conditions, or display general public safety messages.
Speed bumps are a class of traffic calming devices that use vertical deflection to slow motor-vehicle traffic in order to improve safety conditions. Variations include the speed hump, speed cushion, and speed table.
A dual carriageway (BrE) or a divided highway (AmE) is a class of highway with carriageways for traffic travelling in opposite directions separated by a central reservation (BrE) or median (AmE). Roads with two or more carriageways which are designed to higher standards with controlled access are generally classed as motorways, freeways, etc., rather than dual carriageways.
The Manual on Uniform Traffic Control Devices for Streets and Highways is a document issued by the Federal Highway Administration (FHWA) of the United States Department of Transportation (USDOT) to specify the standards by which traffic signs, road surface markings, and signals are designed, installed, and used. Federal law requires compliance by all traffic control signs and surface markings on roads "open to public travel", including state, local, and privately owned roads. While some state agencies have developed their own sets of standards, including their own MUTCDs, these must substantially conform to the federal MUTCD.
Road signs in the United Kingdom and in its associated Crown dependencies and overseas territories conform broadly to European design norms, though a number of signs are unique: direction signs omit European route numbers, and road signs generally use the imperial system of units, unlike the rest of Europe. Signs in Wales (Welsh) and parts of Scotland are bilingual.
In the United States, speed limits are set by each state or territory. States have also allowed counties and municipalities to enact typically lower limits. Highway speed limits can range from an urban low of 25 mph (40 km/h) to a rural high of 85 mph (137 km/h). Speed limits are typically posted in increments of five miles per hour (8 km/h). Some states have lower limits for trucks, some also have night and/or minimum speed limits.
Road traffic control involves directing vehicular and pedestrian traffic around a construction zone, accident or other road disruption, thus ensuring the safety of emergency response teams, construction workers and the general public.
The National Maximum Speed Limit (NMSL) was a provision of the federal government of the United States 1974 Emergency Highway Energy Conservation Act that effectively prohibited speed limits higher than 55 miles per hour (89 km/h). The limit was increased to 65 miles per hour (105 km/h) in 1987. It was drafted in response to oil price spikes and supply disruptions during the 1973 oil crisis. Even after fuel costs began to decrease over time the law would remain in place until 1995 as proponents claimed it reduced traffic fatalities.
Driving in the United Kingdom is governed by various legal powers and in some cases is subject to the passing of a driving test. The government produces a Highway Code that details the requirements for all road users, including drivers. Unlike most other countries in the world, UK traffic drives on the left.
A radar speed sign or speed feedback sign is an interactive sign comprising a speed-measuring device and a message sign generally constructed of a series of LEDs, which displays vehicle speed of approaching motorists. The purpose of radar speed signs is to slow cars down by making drivers aware when they are driving at speeds above the posted limits. They are used as a traffic calming device in addition to or instead of physical devices such as speed bumps and rumble strips.
Road speed limit enforcement in the United Kingdom is the action taken by appropriately empowered authorities to attempt to persuade road vehicle users to comply with the speed limits in force on the UK's roads. Methods used include those for detection and prosecution of contraventions such as roadside fixed speed cameras, average speed cameras, and police-operated LIDAR speed guns or older radar speed guns. Vehicle activated signs and Community Speed Watch schemes are used to encourage compliance. Some classes of vehicles are fitted with speed limiters and intelligent speed adaptation is being trialled in some places on a voluntary basis.
In legal terminology, the assured clear distance ahead (ACDA) is the distance ahead of any terrestrial locomotive device such as a land vehicle, typically an automobile, or watercraft, within which they should be able to bring the device to a halt. It is one of the most fundamental principles governing ordinary care and the duty of care for all methods of conveyance, and is frequently used to determine if a driver is in proper control and is a nearly universally implicit consideration in vehicular accident liability. The rule is a precautionary trivial burden required to avert the great probable gravity of precious life loss and momentous damage. Satisfying the ACDA rule is necessary but not sufficient to comply with the more generalized basic speed law, and accordingly, it may be used as both a layman's criterion and judicial test for courts to use in determining if a particular speed is negligent, but not to prove it is safe. As a spatial standard of care, it also serves as required explicit and fair notice of prohibited conduct so unsafe speed laws are not void for vagueness. The concept has transcended into accident reconstruction and engineering.
Road signs in Canada may conform to the Manual of Uniform Traffic Control Devices for Canada (MUTCDC) by the Transportation Association of Canada (TAC) for use by Canadian jurisdictions. Although it serves a similar role to the MUTCD from the US Federal Highway Administration, it has been independently developed and has a number of key differences with its American counterpart, most notably the inclusion of bilingual (English/French) signage for jurisdictions such as New Brunswick with significant anglophone and francophone population, and a heavier reliance on symbols rather than text legends.
Speed limits in the United States vary depending on jurisdiction. Rural freeway speed limits of 70 to 80 mph are common in the Western United States, while such highways are typically posted at 65 or 70 mph in the Eastern United States. States may also set separate speed limits for trucks and night travel along with minimum speed limits. The highest speed limit in the country is 85 mph (137 km/h), which is posted on a single stretch of tollway in exurban areas outside Austin, Texas. The lowest maximum speed limit in the country is 30 miles per hour (48 km/h) in American Samoa.
Road signs in Armenia are similar to the signs of other post-Soviet states and most European road sign systems. Armenia is a signatory of the Vienna Convention on Road Traffic and the Vienna Convention on Road Signs and Signals. The Ministry of Transport regulates these icons, while the police enforces them. Road signs ensure transport vehicles move safely and orderly, as well as, to inform both pedestrians and motorists of traffic rules.
