In the south, U. In the east, U. In the west, U. The interstate highway numbering system is similar to the U. Main interstates get one- or two-digit numbers, while loops and spurs get three-digit numbers that reflect their parent roads.
To prevent confusion, one important difference distinguishes interstates from U. Fleming announced selection of the first 37, miles. The routes had been proposed by the State highway agencies and reviewed by the Department of Defense. However, neither the act nor later legislation in the 's authorized funds specifically for the Interstate System.
As a result, progress on construction was slow. 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 It served as a catalyst for the System's development and, ultimately, its completion. Title I of the Act increased the System's proposed length to 41, miles.
It also called for nationwide standards for design of the System, 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 project cost at 90 percent. Revenue from the Federal gas and other motor-vehicle user taxes was credited to the Highway Trust Fund to pay the Federal share of Interstate and all other Federal-aid highway projects.
In this way, the Act guaranteed construction of all segments on a "pay-as-you-go" basis, thus satisfying one of President Eisenhower's primary requirements, namely that the program be self-financing without contributing to the Federal budget deficit. The Federal-Aid Highway Act of called for uniform geometric and construction standards for the Interstate System.
Examples of design standards for the Interstate System include full control of access, design speeds of 50 to 70 miles per hour depending on type of terrain , a minimum of two travel lanes in each direction, foot lane widths, foot right paved shoulder, and 4-foot left paved shoulder. Initially, the design had to be adequate to meet the traffic volumes expected in Later, the requirement was changed to a more general year design period to allow for evolution of the System.
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 numbered run east and west.
The number of digits tells you whether an interstate connects multiple metro areas, or exists solely within a single metro area. One and two-digit interstates span multiple regions, while three-digit interstates are more local. The rest of the system flows from this most basic starting point.
Thus, for example, the name I was reserved for the farthest east major national cross-country interstate that traverses a north-south route. Likewise, the name I was reserved for the farthest south major interstate traversing an east-west route. Image by the author. The short and inglorious I, shown in red. Public domain image. There are a few very short two-digit interstates that probably should have gotten three-digit numbers instead. Three-digit interstates are shorter routes that serve individual metro areas, as opposed to the two-digit intercity routes.
They connect to longer two-digit routes, and act as beltways, spurs, or connectors.
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