Freeway
Freeways have high speed limits, multiple lanes for travel in each direction, and a large separation (either through distance or high crash barriers) between the lanes travelling in opposite directions. Crossroads are bypassed by grade (height) separation using underpasses and overpasses, with freeway entrances and exits being limited in number and designed so as to ensure that vehicles do not disrupt the main flow of traffic as they enter or leave the freeway. Freeways do not usually have traffic lights, but expressways do, in places where this distinction is made.
The United States definition, as accepted by civil engineers, is that an expressway is any highway to which adjoining property owners do not have a legal right of access. A freeway is an expressway which is free-flowing; that is to say, there are no traffic conflicts on the main line of the highway which must be mediated by a traffic signal, stop signs, or related traffic controls. Another way to look at it is that an expressway is limited-access, and a freeway is controlled-access, but this distinction is not universally accepted. Many non-engineers misapprehend the "free" in "freeway" to mean that such a highway must be free of charge to use.
Because abutters do not have the right of access that they would on an ordinary public way, the authority undertaking construction of a freeway is frequently required to provide alternate means of access to those landowners. This is frequently accomplished, in areas lacking a dense surface street network, by construction of two uncontrolled roads parallel to and on either side of the freeway, known as frontage roads. In Texas, where this pattern is perhaps at its zenith, such roads are frequently constructed in anticipation of a future freeway corridor, as many as ten years in advance, in order to influence development patterns on the adjoining land. Frontage roads are also often constructed in more densely-developed areas as a means to provide convenient direct access to and from the parallel freeway while minimizing the need for interchanges at every major cross street.
The concept of limited-access automobile highways dates back to the New York City area Parkway system, which began to be constructed in 1907–1908. Designers elsewhere also researched these ideas, especially in Germany, where the Autobahn became the first national freeway system. On December 30, 1940 California opened its first freeway, the Arroyo Seco Parkway, now called the Pasadena Freeway, which connected Pasadena with Los Angeles. Today, many freeways in the United States belong to the extensive Interstate highway system. Almost all interstates are freeways, but the earlier United States highway system and the highway systems of U.S. states also have many sections that are limited-access (though these systems are mostly composed of uncontrolled roads). Only a handful of sections of the Interstate system are not freeways, such as I-81 as it crosses the American span of the 2-lane Thousand Islands Bridge.
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Nomenclature
In the US, the terms expressway and freeway are legally defined by federal regulation and under the laws of most states according to civil engineering usage described above. However, the distinction between these two terms is not universal, and in several states which built freeways very early on (including Connecticut, Illinois, Massachusetts, New Jersey, New York, and Pennsylvania), the terms expressway and freeway have the same meaning, and usually expressway, an older usage, is preferred. (In New Jersey and Pennsylvania, newer roads are often officially styled freeways, where older roads retain the title "expressway".) In the rest of the country, freeway is the usual term; however, the distinction between freeways and expressways is not always as clear or well-understood as it is in California, which has many of both kinds of highway.
Freeways have been constructed both between urban centres and within them, making common the style of suburban development found near most modern cities. As well as reducing travel times, the ease of driving on them reduces accident rates, though the speeds involved also tend to increase the severity and death rate of the crashes that do still happen.
Freeways come under heavy criticism from environmentalists, who argue that freeway expansion is self-defeating, in that expansion will just generate more traffic. This is the debated induced demand hypothesis.
Progress has been made in making U.S. freeways and expressways more efficient however, adding high-occupancy vehicle lanes (HOV lanes) to discourage the typical no-passengers driving patterns, even building new roads with train tracks down the median (or overhead) instead of extra lanes. Intelligent transportation systems (ITS) are also increasingly used, with cameras to monitor and direct traffic, so that police, fire, ambulance, tow, or other assistance vehicles can be dispatched as soon as there is a problem, and to warn drivers via variable message signs, radio, television. and the web to avoid problem areas. Research has been underway for many years on how to partly automate cars by making smart roads with such things as buried magnets to guide sensor-equipped vehicles, with on-board GPS to determine location, direction, and destination. While these systems may eventually be used on surface streets as well, they are most practical in a freeway setting.
In the United States, a very few short privatized toll freeways have also been built by private companies with mixed success.
See also
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