Ballpark Estimate: $114 billion (1956-1991 dollars); $500 billion (2008 dollars)
Holding the distinction of being the largest in the world, the Interstate Highway System is a coast to coast network of state-owned roads. It is a system of high-speed highways that serves every major city in the United States for the transportation of products and goods, personal travel, and for business.
Original Conception – 1956
Conceived during the Eisenhower administration in 1956, the concept was adopted through the strong efforts of the President to meet the challenges of a more mobile society. As an extra benefit to the country, the sprawling web of superhighways would not only provide a more effective method for commercial and private transportation, but also had the potential for providing more avenues of mobility for any military contingency, as well as the means for evacuating major cities in emergencies and national disasters.
There are two categories of Interstates, the primary Interstates and the auxiliary Interstates. Over the years we’ve become quite familiar with the numbered red, white, and blue shields that identify each of the Interstate Highways. The numbering system was adopted in 1957 and revised in 1973 by the American Association of State Highway and Transportation Officials (AASHTO). The association mandated that all Interstate Highways would be identified with either a two or a three-digit number. However, the two-digit number could only be used on Interstates designated as “primary” Interstate Highways. And to be more specific, the two-digit number had to be an even number if the Interstate was an east to west highway such as I-90, or an odd number if it was a North to South primary highway such as I-95.
Complex Naming Schemes
If that wasn’t enough, of all the primary Interstates that carry an odd or even two-digit number, if the Interstate was also classified as a major artery that carried vehicular traffic long distances, it had to be identified with a number divisible by five. Some states have used Interstate signs that also included the highway’s heading, for example I-00E and I-00W. Although AASHTO ruled against such markings, some of them still remain.
The three-digit number is allowed for used on auxiliary Interstates. These are the so-called circumferential highways and spur highways located primarily in urban areas.
These auxiliary Interstates always branch off from a “parent” Interstate Highway. Although there are exceptions, in most cases the three-digit number must consist of a single digit prefixed to the number of the primary Interstate nearby, such as I-495. However, if the auxiliary Interstate returns to its “parent”, it is called a circumferential Interstate and is given an even first digit. If the Interstate does not return to its parent, it is called a spur Interstate and given an odd first digit. Despite the ban imposed on primary Interstates signs, however, auxiliary Interstates are allowed to use north/south, east/west identifications.
The longest East-West Interstate Highway is I-90, which travels from Boston to Seattle, a distance of 3,100 miles. The longest in the North-South direction is I-95. That Interstate extends from the Canadian border southward to Miami, a total of 1,927 miles.
While most Interstate Highways have exit signs, the scheme for identifying the exits varies from state to state. For instance, in most states the exit number also identifies the number of miles traveled on that Interstate. In those states the exit number (which is also the mileage count) will increase as one travels from the West to the East but for Interstates aligned in a North-South direction (or odd numbered), the exit number will increase as one travels from the South to the North. In the Northeast, the states label the exit numbers sequentially without any reference to the number of miles traveled. These states include Connecticut, Massachusetts, Rhode Island, New Hampshire, New York, Vermont, New Hampshire, and Delaware.
The initial construction of the Interstate, as proposed in 1956, was completed in September of 1991 and at the time had a total length of approximately 40,000 miles.
Actual Cost to build the Interstate Highway System was $114 Billion over 35 years ago, and $500 billion in 2008 dollars.
Today, more than half of the costs for construction and maintenance of Interstate Highways comes primarily from gasoline taxes and tolls; the balance being paid by the federal government. However, as the cost of maintaining the present Interstates as well as constructing new ones has grown significantly, it is highly likely that many primary Interstate Highways will be converted into turnpikes (toll roads) to help defray this growing expense.
Whatever the costs, however, the Interstate Highway System has proven to be instrumental in transforming the country, its economy, and American society. It has grown in proportion to our dependency on being mobile by providing us all with the means to travel longer distances quickly and inexpensively. Also, to take advantage of this greater mobility the Interstate Highway System made it possible for a whole range of markets, carriers, and industries to emerge. And finally, as the number of industries grew so did the number of auxiliary Interstate Highways which in turn instigated the suburbanization of our major cities.