Controlled-access highway
Environmental effects

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 Elevated Highway), Boston (Central Artery), San Francisco (Embarcadero Freeway), Seattle (Alaskan Way Viaduct), 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 employed in Madrid and Prague, as well as 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 freeway, 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 toward 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 the US Interstate Highway System, which began in the late 1950s, led to the demolition of thousands of city blocks and the dislocation of many more thousands of people. The citizens of many inner city areas responded with the freeway and expressway revolts. Through the study of Washington's response, it can be shown that the most effective changes came not from executive or legislative action, but instead from policy implementation. One of the foremost rationales for the creation of the United States Department of Transportation (USDOT) was that an agency was needed to mediate between the conflicting interests of interstates and cities. Initially, these policies came as regulation of the state highway departments. Over time, USDOT officials re-focused highway building from a national level to the local scale. With this shift of perspective came an encouragement for alternative transportation, and locally based planning agencies.

At present, freeway expansion has largely stalled in the United States, due to a multitude of factors that converged in the 1970s: higher due process requirements prior to taking of private property, increasing land values, increasing costs for construction materials, local opposition to new freeways in urban cores, the passage of the National Environmental Policy Act (which imposed the requirement that each new federally funded project must have an environmental impact statement or report) and falling gas tax revenues as a result of the nature of the flat-cent tax (it is not automatically adjusted for inflation), the tax revolt movement, and growing popular support for high-speed mass transit in lieu of new freeways.
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