Decoding the American Interstate System

I have realized that a lot of people are confused about the way that highways work in the United States. Many people seem to think that interstates are given numbers at random, but this is actually not the case. Understanding the way that interstate numbers work can actually be extremely helpful. For example, if you are lost on a long road-trip, knowing what number interstate you are on can give you great hints about where you might be! I will give some basic guidelines to help understand the way that interstates are numbered.

Trans-National Interstates Have Two Digits: The longest interstates in the country have two numbers, i.e. I-90, I-15, I-80. Numbers increase from south to north and from west to east. In the Northeast, you are likely to be travelling on I-90 or I-95 while in the Southwest you are probably going to use I-10 or I-15.

North-South Highways End in Odd Numbers: If you are travelling on an interstate that ends in an even number, you know that you are moving north or south. Interstates that are divisible by 5 are major arterites; this means that you are most likely heading for a major city.

East-West Highways End in Even Numbers: If your interstate ends in an even number, you know that you are travelling east or west.

Three Digit Interstates Pass Through Cities: If an interstate has three digits, it is short and serves a specific metropolitan area. The second two digits are the same as the two digit interstate that the route separates from. For example, I-495 would be connected to I-95. If the first digit is even, the route is a beltway, meaning that it separates from the original highway and later rejoins it. If the first digit is odd, it is a spur route which leaves separates form the original highway and does not reconnect to it.

Exit Numbers Increase From The South or West: If you are travelling on an East-West interstate, the lowest exit number will be found at the western border of a state while when traveling North-South, the lowest exit number is at the souther border of a state.

Now for a question to test your understanding. If you are at the interchange of I-10 and I-95, where are you most likely to be?

A. Denver, Colorado
B. Jacksonville, Florida
C. Los Angeles, California
D. Boston, Massachusetts

If you chose Jacksonville you are correct! Having an understanding of these rules can help to increase your sense of direction when driving in unfamiliar areas and also have a better idea of which routes to take over long-distances.