Interstate Highway

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View of Interstate 25

The Interstate Highways (or Interstates for short ) are a trunk road network in the USA and the counterpart to the European highways . They complement the highways that correspond to the German federal highways . The route network of the Interstate Highways was 77,556 kilometers (48,191 miles ) in 2016 . There are speed limits on all interstates that are set by the respective states.

The name of the entire road system is Dwight D. Eisenhower National System of Interstate and Defense Highways ( Interstate Highway System or Interstate System ). The first interstates were built in the 1950s on the initiative of then US President Eisenhower .


The I-5 in California
The Merritt Parkway in Connecticut - one of the oldest highways in the US

The first federal highway commissioned by the federal government was The National Road westbound from Maryland, established by law of March 1806. Construction began in Cumberland, Maryland in July 1811 and reached Vandalia, Illinois in 1839 .

The construction of the Bronx River Parkway in the state of New York began as early as 1907. In 1924 it was opened as the first pure motor road, which however did not carry highway status. The national highway system began in November 1921 with the Federal Aid Highway Act , which led to an intensive expansion of the system. In 1938 the Long Island Parkway was opened. Merritt Parkway in Connecticut opened that same year . The first section of the Pennsylvania Turnpike was opened to traffic in 1940. The New Jersey Turnpike opened in 1946.

At the same time, regional motorway networks emerged on the east coast, especially in the states of New York and Pennsylvania , which systematically opened up the area in the 1920s and 1930s.

After the Second World War, US President Dwight D. Eisenhower planned with the revised Highway Act of June 29, 1956, to create a motorway network based on the German model, essentially financed by the mineral oil tax , which could be used both civilly and militarily. The newly built interstate highways should complement the network of US highways, but not replace them.

Eisenhower and his planning team originally only wanted to build a network between cities and settlement centers. It was not intended that the highways would lead into or cut through the urban areas. Only the overland shares should be paid from the mineral oil tax. The cities themselves should then have connected this network to their roads. Because of the high land costs, the inner-city connecting roads would have been planned with significantly less capacity; they should have been financed according to usage in order to provide an incentive to avoid traffic. This concept was abandoned because the members of the Congress, who came mainly from urban areas, would probably not have approved the use of federal funds mainly in the countryside. In addition, 90% of the funding of the program developed from federal funds for politics into an instrument of church tower politics , English pork barrel . By routing the interstate highways in and through the city centers, not only could property interests be promoted, but large-scale urban renewal projects could also be motivated.

Since 1991, construction of the interstate system has been deemed complete, although new sections of the route are still being built. The original cost estimate of 25 billion US dollars within twelve years has been exceeded by far; $ 114 billion has been spent in 35 years.

Sign for Interstate 95


On maps and street signs, Interstate Highways are identified by a blue coat of arms with a white number and a red horizontal stripe above the number. In some states, the state is listed above the street number. Inner-city alternative routes to the freeways - so-called business routes - use a sign with a green background color, which is often confused with an interstate sign. Green signage is used on the highways.

Numbering system

The Interstate Highways numbering scheme is also administered by the American Association of State Highway and Transportation Officials ( AASHTO ). Major interstates are given one to two-digit numbers. Even numbers run in an east-west direction, odd numbers in a north-south direction. (In some cases, even and odd numbered interstates use the same stretch of route.) The north and east, the higher the street number. Interstates, the number of which can be easily divided by 5, are the most important routes that lead over particularly long distances.

Three-digit numbers indicate ring roads and feeders to more important one- and two-digit interstate highways. They are often awarded for different routes in several states at the same time. Motorway rings around larger cities often start with an even number, whereas feeder routes start with an odd number. The Interstate 238 in Oakland was for the California State Route named 238th It is the only interstate with a three-digit number that does not have a two-digit "parent route" (there is no Interstate 38).

I-355 near Chicago

Speed ​​limits

Originally, the interstate highways were supposed to allow a cruising speed of 70 to 80 mph (113 to 129 km / h) on flat stretches . In 1974 the speed limit was lowered to 55 mph (89 km / h) in order to save gasoline after the 1973 oil crisis . After the end of the oil crisis, the speed limit to promote road safety was maintained, which, however, met with little approval, especially in the sparsely populated states away from the big cities. It is true that the federal government had no legislative competence on this issue; Meanwhile, states that made different regulations threatened the suspension of federal funds for road construction , so that no federal state left.

In 1987, the speed limit on highways outside of urban areas was increased to 65 mph (105 km / h) if the states allowed it; 55 mph was maintained in urban areas.

Some states raised the speed limit to 70 or 75 mph (113 and 121 km / h), respectively. The state of Montana abolished the speed limit on interstate highways and encouraged motorists to drive “prudently and sensibly”. This regulation was declared unconstitutional because of its vague wording and a speed limit of 75 mph was introduced instead.

Since 1995, several states in the western United States introduced a maximum speed of 80 mph (129 km / h). Texas also reports 80 mph for a corridor west of the state along Interstate 10 . The road with the highest speed limit is a section of Texas State Highway 130 at 85 mph (137 km / h), so not an interstate highway (as of mid-2017).

Map of the Interstate Highways


Construction and maintenance are financed through tolls and mineral oil taxes. Many of the east coast highways built before 1956 still have toll booths. However, motorway routes built later are generally free of charge.

The federal government pays grants for the construction and maintenance of the roads, but links these payments with demands that the states must adapt their road traffic law to the ideas of the federal government in return.

As the suburbs grew, so too did the transport links, which were financed from funds for the construction of new interstates. Some interstate highways, such as I-35, are run by private companies in order to reduce the costs of the State Departments of Transportation. How the interstate will be financed in the future is not yet clear. It is possible that the number of toll roads will increase or there will be more HOV / HOT lanes , toll lanes in metropolitan areas such as the metropolitan areas of San Diego , Salt Lake City , Minneapolis / Twin Cities , Houston , Dallas , Atlanta and Washington, DC will give.

Not all interstate highways cross the borders of different states. Some run only within one state, e.g. B. Interstate 210 in California. The highways in Hawaii are also known as the Interstate Highway. The highways in Alaska and Puerto Rico are also financed from the same funds, but not called Interstate Highways.

Use in the event of a disaster

The Interstate Highways were designed for both civil and military use. For example, the interstate highways system enables the rapid evacuation of large cities in the event of an impending nuclear war or an impending natural disaster. In the event of a disaster, all lanes, including those in the opposite lane, are released for evacuation of the population. An example of this was New Orleans before Hurricane Katrina .

See also

Web links

Commons : Interstate Highway System  - collection of pictures, videos and audio files

Individual evidence

  1. ^ US Department of Transportation: Highway Statistics 2016
  2. Marlon G. Boarnet: National transportation planning: Lessons from the US interstate highways . In: Transport Policy , Volume 31, January 2014, Pages 73–82, doi: 10.1016 / j.tranpol.2013.11.003
  3. Atlantic Citiey: What the Interstate Highway System Should Have Looked Like , January 14, 2014
  4. ^ David Field: On 40th birthday, interstates face expensive midlife crisis. Insight on the News, Jul 29, 1996, 40-42.
  5. Atlanta Journal-Constitution: 1st toll project proposed for I-20 east Plan would add lanes outside I-285 ( memento of the original from October 25, 2007 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice. @1@ 2Template: Webachiv / IABot /
  6. HOV in Atlanta ( Memento of the original from July 28, 2012 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice.  @1@ 2Template: Webachiv / IABot /