How are Highways Numbered?

Do you ever wonder how the state and interstate highways are numbered? As I was driving into work today I got to thinking, why the 95 in I-95 or the 295 in I-295? I remember learning about a national system of highways in school but couldn’t remember the specifics about how the numbers were chosen. Are they chronological? Are they random? Do the numbers actually mean anything? These questions inspired today’s post.

Brief History

What we know today as the interstate system in North America actually dates back to 1930’s. Before then, there were no federal funded transcontinental roads. Instead of the Federal Highway Administration (FHWA), there was an organization known as the Bureau of Public Roads (BPR). In the late 1930’s the BPR conducted a study which showed that using toll networks for national highways would not be feasible and recommended that a toll-free network be constructed. There were several legislative acts after this that called for the construction of national highways but none of them provided funding. The funding problem was solved when President Dwight D. Eisenhower enacted Federal-Aid Highway Act of 1956. The interstate system was originally called The National System of Interstate and Defense Highways. It has since been changed to the Dwight D. Eisenhower System of Interstate and Defense Highways.

What do the Numbers Mean?

When The Federal-Aid Highway Act of 1956 was enacted, construction and spending standards were developed. Part of what Congress had to figure out was how to actually name and keep track of each of the highways. Basically the numbers break down like this:

For Interstates:

Odd numbered interstates run north to south
-Lower numbered interstates are in the west (ex. I-15 running from CA to MT)
-Higher numbered interstates are in the east (ex. I-95 running from ME to FL)

Even numbered interstates run east to west
-Lower numbered interstates are in the south (ex. I-10 running from CA to FL)
-Higher numbered interstates are in the north (ex. I-90 running from WA to MA)

For Routes/U.S. Highways:

Odd numbered routes run north to south
-Lower numbered routes are in the east (ex. Route 9 running from CA to WA)
-Higher numbered routes are in the west (ex. Route 99 running from DE to Canada)

Even numbered routes run east to west
-Lower numbered routes are in the north (ex. Route 22 running from OH to NJ)
-Higher numbered routes are in the south (ex. Route 66 running from CA to IL)

Local Numbers

If you live in the tri-state area (PA, NJ, and DE) you are probably familiar with I-95, I-295 and Route 322. I-95 is a main interstate and it is also the longest north and south running route. I-295 is considered to be an “auxiliary route”. This is also known as a bypass because it branches off of I-95 but eventually connects back to it. 322 is actually a spur of Route 22. What this means is that Route 322 acts as a branch onto another road but does not usually reconnect with the major interstate. Majority of the time you can tell the difference between a spur and a bypass because of what the first digit is in a three digit highway; spurs are usually odd and bypasses are usually even.

There is actually much more information available about the highway systems in general. Hopefully this post made sense of some of the numbers you see every day while on the road. If you would like to learn more, please check out some of the resources below that I used while writing this article.

Federal Highway Administration

How Stuff Works

This blog post was written by Kelly Woods for Murphy Ford