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5 Facts About the Interstate Highway System

The Interstate Highway system has become a big part of our every day lives, our travel plans.  We take it to work and to play.

It’s the fastest way to travel between point A and point B.  This, of course, does depend on how much of your route is interstate and how much consists of secondary or “surface level” roads.

The interstate highway is considered a limited access highway.  Accessibility comes from ramps linking to secondary roads.  Very few commercial services are available, aside from rest areas with vending machines.

Some other limited access highways, such as the Florida Turnpike, have more services like gas stations, gift shops, and even restaurants.

MUTCD M1-10a

1.) “Interstate Highway” is actually an abbreviation of the official name.

The “Dwight D. Eisenhower National System of Interstate and Defense Highways” is the official name of this system of highways.

President Dwight Eisenhower championed the interstate highway system, and signed the Federal Aid Highway Act of 1956 into law.  The President’s fondness for system came from his time in Germany as General in the U.S. Army during World War II.  He witnessed the functionality of the German Autobahn system first hand as war operations were wrapping up.

2.) The first Canada-to-Mexico Interstate was Interstate 5

interstate highway system
Image courtesy of Noppawat Charoensinphon on Flickr.

Interstate 5 was one of the originally funded highway projects, beginning in 1956.  However, it was not a Canada-to-Mexico interstate until a it’s final route segment near Stockton, California was completed in 1979.

Interstate 5’s southern terminus is in San Ysidro, California, opposite the Mexican border from the popular tourist destination of Tijuana.

Interstate 5’s northern terminus is in Blaine, Washington, opposite the Canadian border from Surrey, British Columbia.

Its total length is 1,381 miles.

3.) The first coast-to-coast Interstate was Interstate 80.

interstate highway system
Interstate 80 in the mountains. Image courtesy of Benjamin Miller on Flickr.

Like Interstate 5, Interstate 80 was an original 1956 highway.

On the west coast, Interstate 5 begins in San Francisco, California; and ends on the east coast in Teaneck, New Jersey, near New York City.

The final segment of Interstate 80 was finished in 1986 in Utah.

Its total length is 2,909 miles.

4.) Interstate Design Standards

The American Association of State Highway and Transportation Officials created a published group of guidelines called A Policy on Design Standards: Interstate System.

Within, certain design standards must be followed in the construction and operation of interstate highways.  In certain situations, some exceptions can be made with a waiver from the Federal Highway Administration.

      • Controlled access using on- and off-ramps, spaced a minimum distance apart.
1.) Mostly, this is seen in extremely rural parts of the western United States where interstates follow formerly secondary roads.  
2.) Another exception was Interstate 275 in near Florida’s Sunway Skyway Bridge where there was a break in the highway to access rest areas until the mid 1990s.


  • Minimum Design Speed: Pertaining to flat, rural areas, the minimum speed should be 70 miles per hour.  50 to 60 miles per hour is generally a minimum in rolling or mountain terrain.  Urban areas are given more careful, case-by-case consideration.
  • Number of lanes shall be a minimum of two in each direction.
EXCEPTION: There is no standard requiring interstates to have a mile-long straightaways every five miles to allow for aircraft landings.


  • Travel lanes must be a minimum of 12 feet in width.
  • Median width shall be a minimum of 36 feet.
  • Minimum overhead clearance to overpasses, signs, and other structures shall be a minimum of 16 feet.
  • Tunnel horizontal clearance is recommended to be a minimum of 44 feet wide, but shall be 30 feet wide.

Click for 10 Signs You’re Approaching a Speed Trap

5.) Numbering System

Even numbered interstates run generally in an east-west fashion, and odd numbered ones run generally in a north-south fashion.

Do some stretches of even numbered interstates run north-south, and vice-versa?  Yes.  Much of even-numbered Interstate 4 in the Orlando area runs north-south.  However, Interstate 4 ultimately covers more ground east-west.

Primary interstate highways have one- and two-digit numbers.

Auxiliary or secondary interstate highways have three-digit numbers.

Examples of auxiliary highways are loops around large metropolitan areas (usually beginning with an even number), or spurs linking primary highways with business districts (usually beginning with an odd number).

There are exceptions to the primary and auxiliary interstates.

Interstate 75 is considered a primary interstate, but bypasses the Florida cities of Tampa and St. Petersburg.  Inner-city Tampa and St. Petersburg are accessed by Interstate 275.  Additionally, St. Petersburg’s downtown area is accessed by two spurs: Interstates 175 and 375.

Any additional facts you’d like to contribute?  Favorite interstate highways?  Least favorites?  Please feel free to comment in the box below.

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