Interstate Highway

The Dwight D. Eisenhower National System of Interstate and Defense Highways, commonly called the Interstate Highway System, is a network of highways in the United States. The Interstate Highway System is a separate system within the larger National Highway System. With very few exceptions, Interstate highways are controlled-access freeways, allowing for safe high-speed driving when traffic permits. They are assigned a special level of funding at the federal level. Despite this federal funding, these highways are owned, designed, built and maintained by the state in which they are located, with the only exception being the federally-owned Woodrow Wilson Bridge on the Capital Beltway (I-95/I-495).

Signage

Interstate Highways are signed by a number on a red, white and blue sign as shown to the right. In the original design, the state was formerly listed above the highway number, but in many states, this area is now left blank. The sign itself measures 36 inches high, and is 36 inches wide for two-digit interstates, or 45 inches for three-digit interstates.

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Business Loop and Business Spur Interstates use a special shield where the red and blue are replaced with green; the word BUSINESS appears instead of INTERSTATE, and the word SPUR or LOOP usually appears above the number.

Related Topics:
Business Loop - Business Spur

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The majority of Interstates have exit numbers. All traffic signs and lane markings on the Interstates are supposed to be designed in compliance with the Manual on Uniform Traffic Control Devices (MUTCD). However, there are many local and regional variations in signage. The state of California is now adapting to an exit numbering system after many years as being the only state in the country that did not use such system.

Related Topics:
Exit number - Traffic sign - Lane - Manual on Uniform Traffic Control Devices - California

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In most states, the exit numbers correspond to the mileage markers on the Interstates (with an exception being I-19 in Arizona, whose length is measured in kilometers instead of miles). Many northeastern states label exit numbers sequentially, regardless of how many miles have passed between exits. On even-numbered Interstates, mileage increases to the east and decreases to the west; and on odd-numbered Interstates, mileage increases to the north and decreases to the south. In both cases, the exit numbers increase and decrease accordingly.

Related Topics:
Mile - I-19 - Arizona - Kilometer

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