A freeway is a road designed for high speeds which has limited access and no surface crossings with other roads or railways. Traffic traveling in opposite directions is usually separated by a barrier or a strip of unpaved land. Vehicles must use an overpass or underpass to cross a freeway and they can only enter via special ramps. Freeways almost always have at least two lanes in each direction and often have several more, particularly in urban areas. Unlike most other roads, bicycles and pedestrians are prohibited from entry. Freeways are sometimes elevated in order to cross over other roads, railroad tracks and waterways, and occasionally they run in trenches and through tunnels.
In the U.S. the word interstate refers to the nation-wide network of freeways but does include many local freeways mainly in urban areas. Terms for freeways in other countries include Autobahn in Germany, snelweg in the Netherlands, autostrada in Italy and autopista in Spain.
One of the most common reasons given for constructing freeways is to increase traffic speeds by eliminating surface crossings with other roads and rail lines. Closely related to this is the goal to reduce traffic congestion, both through this increase in speed and by diverting traffic from other roads. It has also been frequently claimed that this reduction in crossings increases traffic safety. Another claimed benefit is reduced fuel consumption and reduced air pollution by allowing vehicles to operate at roughly steady speeds rather than repeated cycles of stopping and starting. Still another reason for constructing freeways, which was often given in the U.S. in the past, was "slum clearance."
On the surface, these appear to be very powerful arguments for the construction of new freeways and the maintenance of existing ones. However, the reality is far more complicated. In fact, freeways have generally failed in each of their stated goals. That is, they often did not reduce congestion and increase speeds, but often actually increased congestion and reduced speeds. This is because they encouraged more automobile trips, resulting in "induced demand". They also contributed to growing air pollution.
Freeways have also had adverse effects on neighborhoods in cities. One reason is because they often require the use of large swaths of land, thereby necessitating the demolition of many homes and businesses. This has particularly affected low income and minority neighborhoods because planners tend to route freeways through such areas rather than wealthier neighborhoods as the latter have greater political power to resist them. In addition, the remaining living areas near freeways are severely affected by the noise and air pollution.
This damage became increasingly apparent as more and more freeways were built, and it led to numerous freeway revolts in the U.S. from the 1960s. More recently there has been a trend towards the removal of freeways, with numerous such projects completed or planned.