Interstate highway
The Dwight D. Eisenhower System of Interstates and National Defense Highway System, commonly called the interstate highway system, is a network in the United States of interstate highways or simply interstates.
Nearly every interstate highway is a controlled-access superhighway or freeway. The interstate system and National Defense Highway System was modeled after the German autobahn system and started under President Dwight D. Eisenhower in 1956.
While the name implies highways that cross U.S. state lines, many interstates don't. Rather, it is the system of interstates that connects states. There are interstate highways in Hawaii, funded in the same way as in the other states, but entirely within the islands of Hawaii. Similarly, both Alaska and Puerto Rico have public roads that receive funding from the interstate program, though these routes are not signed as interstate highways.
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2 Speed limits 3 Dual Purpose Design 4 Signage 5 Naming of the highways 6 See also 7 External links |
Financing
Often, depending on the part of the country, these roads are called freeways. The term is also used to describe toll-free superhighways, but can sometimes also be used to describe such roads whether there is a toll or not, because they are free-flowing. Almost all of the construction and maintenance cost is funded through user fees, primarily gasoline taxes, collected by states and the federal government, and tolls collected on toll roads and bridges. In the eastern United States, sections of some Interstate highways planned or built prior to 1956 are operated as toll roads, and are often called turnpikes.
The heavy role of the federal government in road financing has allowed it to pass laws in areas outside of the direct power of the government. By threatening to withhold highway funds, the federal government has been able to force state legislatures to pass laws which increase the drinking age to 21 and for a number of years, reduce the maximum speed limit to 55 miles per hour.
Speed limits
Speed limits vary according to location. By initial planning, the Interstate system was designed to be able to move traffic at speeds of 75 to 80 miles per hour (121 to 129 km/h) except in limited stretches (such as steep mountain passes) where many vehicles cannot maintain such speeds. In 1974, the maximum speed limit allowed on interstate highways (along with all others in the country) was reduced to 55 mph (89 km/h) as a gasoline conservation measure in response to the 1973 energy crisis. After the end of the embargo this restriction was continued, being justified as a safety measure, but it was very unpopular, especially in western states; it was relaxed in 1987 to allow 65 mph (105 km/h) speeds in most areas if the states so chose, and eliminated in 1995, fully returning speed limits to state control.
Traffic lights are limited to toll booths (and toll booths are limited to grandfathereded roads and bridges), draw bridges, and ramp meters (metered flow control) for lane merging during rush hours.
Dual Purpose Design
In addition to being designed to support automobile and heavy truck traffic, interstate highways are also designed for use in military and civil defense operations within the United States, particularly troop movements.
One potential civil defense use of the Interstate highway system is for the emergency evacuation of cities in the event of a potential nuclear war. Although this use has never happened, the Interstate highway system has been used to facilitate evacuations in the face of hurricanes and other natural disasters. An option for maximizing throughput is to reverse the flow of traffic on one side so that all lanes become outbound lanes.
A widespread but false urban legend states that one out of every five miles of the Interstate highway system must be built straight and flat, so as to be usable by aircraft during times of war.[1]
On maps and the road, the highway is indicated by a number on a red, white and blue sign in a shape of a shield. On signs on the side of the road, the current state was formerly listed above the highway number, but in some states this area is now left blank. The Interstate shield is not to be confused with the similar-shaped green shield for a business route or loop, which gives access to and from a business district without meeting the specifications for Interstate highways.
Three-digit route numbers, consisting of a single digit prefixed to the number of a primary Interstate highway, are used to designate highway extensions, spurs (odd prefixes), and bypasses (even prefixes) that connect to the main highway within an urban area. For example, there are many extensions to I-80 in the San Francisco Bay Area: I-280 connects San Francisco and San Jose; I-380, I-580, I-680, I-780, I-880, I-980 are also major highways. (I-480 was also an extension before it was demolished following local popular opposition). Three-digit route numbers may be repeated in different states for different roads.
Interstate 238 near Oakland, California is one of two exceptions to the numbering scheme, as no Interstate 38 exists (this number exists because Interstate 238 replaced a segment of California Highway 238 and changing the number would have split the California Highway in two segments. The original number was retained to keep the California Highway contiguously numbered). The other exception is I-99 in Pennsylvania which was written into law as I-99 by Pennsylvania Congressman Bud Shuster, as it is west of several Interstates that are numerically less than 99.
Some old local highways may be renamed when included in the federal system. For example, part of California highway 17 connecting Oakland and San Jose was renamed as I-880 in the mid 1980s. Part of the original California Highway 17 still connects San Jose and Santa Cruz.Signage
Naming of the highways
The numbering scheme for the Interstate highway system is administered by the American Association of State Highway and Transportation Officials (AASHTO). Primary Interstate highways (or main line interstates) are given one- or two-digit route numbers. Within this category, even-numbered highways go generally east-west, and odd-numbered highways go generally north-south. (However, in some places two or more Interstate highways run along the same physical road, and such a road may be "east" for one route and "north" for the other.) Odd numbered routes increase from west to east; and even numbered routes increase from south to north. Numbers divisible by 5 are roads which go all the way (or nearly all the way) from one border of the U.S. to another. For example, I-5 runs from Canada to Mexico along the west coast while I-95 runs along the east coast. In addition, I-10 runs from Los Angeles, California to Jacksonville, Florida while I-80 runs from San Francisco to Fort Lee, New Jersey. There is also an I-90 that runs from Seattle to Boston, and shares a portion of its routing with I-80.