Variable-message signA variable- (also changeable-, electronic-, or dynamic-) 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.
Assured clear distance aheadIn 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.
Traffic congestionTraffic congestion is a condition in transport that is characterized by slower speeds, longer trip times, and increased vehicular queueing. Traffic congestion on urban road networks has increased substantially since the 1950s. When traffic demand is great enough that the interaction between vehicles slows the traffic stream, this results in congestion. While congestion is a possibility for any mode of transportation, this article will focus on automobile congestion on public roads.
Interstate Highway SystemThe Dwight D. Eisenhower National System of Interstate and Defense Highways, commonly known as the Interstate Highway System or the Eisenhower Interstate System, is a network of controlled-access highways that forms part of the National Highway System in the United States. The system extends throughout the contiguous United States and has routes in Hawaii, Alaska, and Puerto Rico. The United States Congress first funded roadways through the Federal Aid Road Act of 1916, and began an effort to construct a national road grid with the passage of the Federal Aid Highway Act of 1921.
AutobahnThe Autobahn (ˈaʊtoˌbaːn; German plural Autobahnen) is the federal controlled-access highway system in Germany. The official German term is Bundesautobahn (abbreviated BAB), which translates as 'federal motorway'. The literal meaning of the word Bundesautobahn is 'Federal Auto(mobile) Track'. Much of the system has no speed limit for some classes of vehicles. However, limits are posted and enforced in areas that are urbanised, substandard, accident-prone, or under construction.
RoadA road is a thoroughfare for the conveyance of traffic that mostly has an improved surface for use by vehicles (motorized and non-motorized) and pedestrians. Unlike streets, whose primary function is to serve as public spaces, the main function of roads is transportation. There are many types of roads, including parkways, avenues, controlled-access highways (freeways, motorways, and expressways), tollways, interstates, highways, thoroughfares, and local roads.
ParkwayA parkway is a landscaped thoroughfare. The term is particularly used for a roadway in a park or connecting to a park from which trucks and other heavy vehicles are excluded. Over the years, many different types of roads have been labeled parkways. The term may be used to describe city streets as narrow as two lanes with a landscaped median, wide landscaped setbacks, or both. The term has also been applied to scenic highways and to limited-access roads more generally.
Solomon curveThe Solomon curve is a graphical representation of the collision rate of automobiles as a function of their speed compared to the average vehicle speed on the same road. The curve was based on research conducted by David Solomon in the late 1950s and published in 1964. Subsequent research suggests significant biases in the Solomon study, which may cast doubt on its findings. In 1964, Solomon researched the relationship between average speed and the collision rates of automobiles and plotted the results.
Geometric design of roadsThe geometric design of roads is the branch of highway engineering concerned with the positioning of the physical elements of the roadway according to standards and constraints. The basic objectives in geometric design are to optimize efficiency and safety while minimizing cost and environmental damage. Geometric design also affects an emerging fifth objective called "livability," which is defined as designing roads to foster broader community goals, including providing access to employment, schools, businesses and residences, accommodate a range of travel modes such as walking, bicycling, transit, and automobiles, and minimizing fuel use, emissions and environmental damage.
Risk compensationRisk compensation is a theory which suggests that people typically adjust their behavior in response to perceived levels of risk, becoming more careful where they sense greater risk and less careful if they feel more protected. Although usually small in comparison to the fundamental benefits of safety interventions, it may result in a lower net benefit than expected or even higher risks. By way of example, it has been observed that motorists drove closer to the vehicle in front when the vehicles were fitted with anti-lock brakes.
