Interstate highways are something we take for granted and give little thought to, but if you want some Interstate Trivia read the following.

Officially named the Dwight D. Eisenhower National System of Interstate and Defense Highways and commonly called the Interstate Highway System, it had its beginning in the late 1930's. The Federal-Aid Highway Act of 1938 called on the Bureau of Public Roads (BPR), the predecessor of the Federal Highway Administration (FHWA), to study the feasibility of a toll-financed system of three east-west and three north-south superhighways. The BPR's report, Toll Roads and Free Roads, demonstrated that a toll network would not be self-supporting. Instead, the BPR's report advocated a 26,700 mile inter-regional highway network.

In 1941 President Franklin D. Roosevelt appointed a National Interregional Highway Committee to evaluate the need for a national expressway system. The committee's 1044 report, Interregional Highways, supported a system of 33,900 miles plus an additional 5,000 miles of urban routes.

The Federal-Aid Highway Act of 1944 was enacted by Congress. The act called for designation of a National System of Interstate Highways to include up to 40,000 miles - "...so located, as to connect by routes, direct as practical, the principle metropolitan areas, cities, and industrial centers, to serve the National Defense, and to connect at suitable points, routes to continental importance in the Dominion of Canada and the Republic of Mexico."

The first 37,700 miles were announced in 1947, routes that had been proposed by state highway agencies and reviewed by the Department of Defense. However, neither the Act of 1944 nor later legislation in the 1940's authorized funds so construction was extremely slow. The Federal-Aid Highway Act of 1952 authorized the first funding for highway construction, but it was only a token amount of $25 million a year for 1954 and 1955. Legislation in 1954 authorized an additional $175 annually for 1956 and 1957.

Under the leadership of President Eisenhower the question of how to fund the Interstate System was resolved with enactment of the Federal-Aid Highway Act of 1956. It served as a catalyst for the System's development and ultimately its completion. The 1956 Act increased the System's proposed length to 41,000 miles. It also called for nationwide standards for design, authorized an accelerated program, established a new method for apportioning funds among the states, changed the name to the National System of Interstate and Defense Highways and set the Federal Government's share of the project at 90% with states paying 10%.

Revenue from the Federal gas and other motor-vehicle user taxes was credited to the Highway Trust Fund to pay the Federal share. This way the Act guaranteed construction of all segments on a "pay-as-you-go" basis, thus not adding to the Federal budget deficit.

Interstate Route Numbering

The Interstate route marker is a red, white and blue shield, carrying the word "Interstate", the State name and the route number. Major interstate routes are designated by one- or two-digit numbers. Routes with odd numbers run north and south while even numbers run east and west. For north-south routes the lowest numbers begin in the west while the lowest numbered east-west routes are in the south. By this method Interstate Route 5 (I-5) runs north-south along the west coast while I-10 lies east-west along the southern border. 

Connecting Interstate routes and full or partial circumferential beltways around or within urban areas carry a three-digit number. These routes are designated with the number of the main route and an even-numbered prefix. Supplemental radial or spur routes connecting with the main route at one end also carry a three-digit number, using the main route with an odd-number prefix. To prevent duplication within a state a progression of prefixes is used for the three-digit numbers. For example, if I-80 runs through three cities in a state, circumferential routes around these cities would be numbered I-280, I-480 and I-680. The same system would be used for spur routes into three cities with routes being numbered I-180, I-380 and I-580. This system is not carried across state lines. As a result several cities in different states along I-80 may each have circumferential beltways numbered as I-280 or spur routes numbered as I-180.

Interstate Interchange (Exit) Numbers

The states typically use one of two methods of numbering Interstate interchanges. The Federal Highway Administration has mandated all states use the Milepost numbering system, but some states have been slow to switch.
 

Interstate System Facts

The Interstate Highway System contains 46,726 miles and below are some trivial facts.

OK, just a few more facts and figures:

The oldest segment of the Interstate system is a portion of the Grand Central Parkway in Queens, New York. It was opened to traffic in 1936 and was later incorporated into the Interstate system as I-278. The Pennsylvania Turnpike between Irwin and Carlisle was opened in 1940 and is now designated as I-70 and I-76. Other early freeways and tool roads were incorporated into the Interstate system rather than building new competing routes.

There are approximately 1,214 rest areas along the Interstate System and there are approximately 15,000 Interchanges (Exits).