Facts from the Federal Highway Administration

18 April 2008

• The interstate system carries 40.3% of single and combination-unit truck travel on all public roads in the United States.

• The interstate system carries about 721,381,000,000 vehicle miles traveled (VMT) a year. About 91,296,000,000 VMT are by heavy single-unit and combination trucks.

• Out of nearly four million miles of public roads in the United States, a total of about 96,712 miles is eligible for Federal-aid highway funds. The interstate system totals 4.8% of mileage eligible for federal aid.

• Only two interstates end at international borders at both termini (Canada and Mexico): I-5 and I-35.

• Texas has more interstate miles than any state - 3,233 miles.

• The average daily traffic on all interstate bridges is 1.9 billion vehicles a day. This total includes 244.8 million trucks.

• The biggest interstate year was 1967, when the states opened 3,354.20 miles. Counting turnpikes (2,303.30 miles) incorporated into the interstate system, a total of 25,641.90 miles had been opened by the end of the year.

• How you refer to interstates says something about you. If you refer to an interstate as, for example, “the 5” or “the 10,” you are from, or lived many years, in the west. If you refer to I-95 or “95,” you probably have spent some time in the east.

• The average age of all interstate bridges is 36 years.

• From 1957 through 2004, vehicles on the interstate system traveled 15.8 trillion miles.

• It is not true that one-in- five miles of the interstate system must be straight so airplanes can land. This widespread myth has no basis in law, regulation, design manual, or fact. Airplanes occasionally land on interstates, not because the interstates are designed for that purpose, but because no alternative is available in an emergency.

• The longest interstate highway is I-90, stretching 3,085 miles from Boston, Massachusetts, to Seattle, Washington.

• If an interstate highway has a one- or two-digit even number, such as I-40, a motorist can tell it is predominantly an east-west highway. One- and two-digit odd numbers, such as I-15, are reserved for north-south routes. Parts of long-distance multi-State roads may have a different cardinal orientation, but the number is based on the termini (i.e., end points). For example, I-94 between Chicago and Milwaukee, is a north-south route, but this segment is part of an east-west route between Port Huron, Michigan, and Billings, Montana. As a result, the route carries an even number.


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