page_title: Controlled-access highway
section_title: Environmental effects
hierarchical_section_title: Controlled-access highway / Environmental effects
caption_attribution_description: English: A1 Motorway tunnel near Agios Konstantinos
context_page_description: A controlled-access highway is a type of highway that has been designed for high-speed vehicular traffic, with all traffic flow—ingress and egress—regulated. Common English terms are freeway, motorway and expressway. Other similar terms include Interstate and throughway and parkway. Some of these may be limited-access highways, although this term can also refer to a class of highway with somewhat less isolation from other traffic.
  In countries following the Vienna convention, the motorway qualification implies that walking and parking are forbidden, and they are reserved for the use of motorized vehicles only.
  A controlled-access highway provides an unhindered flow of traffic, with no traffic signals, intersections or property access. They are free of any at-grade crossings with other roads, railways, or pedestrian paths, which are instead carried by overpasses and underpasses. Entrances and exits to the highway are provided at interchanges by slip roads, which allow for speed changes between the highway and arterials and collector roads.
context_section_description: Controlled-access highways have been constructed both between major cities as well as within them, leading to the sprawling suburban development found near most modern cities. Highways have been heavily criticized by environmentalists, urbanists, and preservationists for the noise,
  pollution, and economic shifts they bring.
  Additionally, they have been criticized by the driving public for the inefficiency with which they handle peak hour traffic.
  Often, rural highways open up vast areas to economic development and municipal services, generally raising property values. In contrast to this, above-grade highways in urban areas are often a source of lowered property values, contributing to urban decay. Even with overpasses and underpasses, neighbourhoods are divided—especially impoverished ones where residents are less likely to own a car, or to have the political and economic influence to resist construction efforts. Beginning in the early 1970s, the US Congress identified freeways and other urban highways as responsible for most of the noise exposure of the US population. Subsequently, computer models were developed to analyze freeway noise and aid in their design to help minimize noise exposure.
  Some cities have implemented freeway removal policies, under which freeways have been demolished and reclaimed as boulevards or parks, notably in Seoul (Cheonggyecheon), Portland (Harbor Drive), New York City (West Side Elevator Highway), Boston (Central Artery), San Francisco (Embarcadero Freeway) and Milwaukee (Park East Freeway).
  An alternative to surface or above ground freeway construction has been the construction of underground urban freeways using tunnelling technologies. This has been particularly employed in the Australian cities of Sydney (which has five such freeways), Brisbane (which has three), and Melbourne (which has two). This has had the benefit of not creating heavily trafficked surface roads and, in the case of Melbourne's Eastlink Motorway, prevented the destruction of an ecologically sensitive area.
  Other Australian cities face similar problems (lack of available land, cost of home acquisition, aesthetic problems and community opposition). Brisbane, which also has to contend with physical boundaries (the Brisbane River) and rapid population increases, has embraced underground freeways. There are currently three open to traffic (Clem Jones Tunnel (Clem7), Airport Link and Legacy Way) and one (East-West Link) is currently in planning. All of the tunnels are designed to act as an inner-city ring road or bypass system and include provision for public transport, whether underground or in reclaimed space on the surface. However, freeways are not beneficial for road-based public transport services, because the restricted access to the roadway means that it is awkward for passengers to get to the limited number of boarding points unless they drive to them, largely defeating the purpose.
  In Canada, the extension of Highway 401 into Detroit, known as the Herb Gray Parkway, has been designed with numerous tunnels and underpasses that provide land for parks and recreational uses.
  Freeway opponents have found that freeway expansion is often self-defeating: expansion simply generates more traffic. That is, even if traffic congestion is initially shifted from local streets to a new or widened freeway, people will begin to use their cars more and commute from more remote locations. Over time, the freeway and its environs become congested again as both the average number and distance of trips increases. This phenomenon is known as induced demand.
  Urban planning experts such as Drusilla Van Hengel, Joseph DiMento and Sherry Ryan argue that although properly designed and maintained freeways may be convenient and safe, at least in comparison to uncontrolled roads, they may not expand recreation, employment and education opportunities equally for different ethnic groups, or for people located in certain neighborhoods of any given city. Still, they may open new markets to some small businesses.
  Construction of urban freeways for t
caption: Tunnel on the A1 Motorway in Greece.
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