On the Road Again:
Interstates Explained
SATURDAY, MAY 27, 2023 -- When I was living in Honolulu a generation or so ago, locals were breathlessly awaiting the completion of the Interstate Highway System in Hawaii.

Everyone but me. As a haole from the mainland, I couldn't even figure out why Hawaii had Interstate Highways. I kept looking out at the Pacific, searching for the bridge to California or the causeway to Oregon. I kept wondering why I was the only one in Honolulu who seemed to notice that Interstate Highways in Hawaii were, by definition, an oxymoron. I went to parties and asked the same question: How can Hawaii have Interstate Highways when they won't connect us to any other state?

I moved away before I got the answer to that poser. But the experience made an impression on me. I became something of an Interstate Highway buff.

Now I know the Interstate Highway system doesn't sound like much of a topic of conversation. I mean, we're not talking about the speed-limit-free German Autobahn here. We're not even discussing the Italian Autostrada, where chic, spotless roadside Autogrill cafes have marble countertops and baristi serve espresso and cappuccino in designer cups.

Sexy the Interstates aren't. But functional is something else. As we head out for our Great American Summer Road Trips, nearly 25% percent of our driving will be on the Interstates. That's astonishing since the approximately 47,000 miles of Interstate highways account for only about 1% of America's roads.

Given the frequency with which Americans use Interstates, it's also astonishing how little we know about them. Few of us, for example, know the history of the system. (For an entertaining backgrounder and map, check in with Matt Rosenberg at ThoughtCo.com.)

Even fewer of us know how to use the Interstate Highways. What's to know, you ask? Well, how about that there's a reason and rhyme to why each Interstate is numbered the way it is? And did you know that, if you understand how the Interstates are numbered, you'll almost never get lost even without GPS?

So give me just a moment to explain how Interstate Highways work. You'll thank me for it next time you're on an Interstate just outside of Palookaville and you don't know which way to turn. Besides, have you seen the price of flying just now? You might have to swap out a flight or two for some road trips in the weeks ahead ...

Even numbers are assigned to roads that travel in an east-west direction. That rule actually applies both to Interstate Highways identified by one or two digits--I-80 in the northern part of the country and I-40 in the south, for example--and U.S. Routes, which are identified by black-and-white signs.

Odd numbers represent roads that travel in a north-south direction. This rule encompasses both the Interstate Highways identified by one or two digits--I-5 along the nation's West Coast and I-95 along the East Coast, for instance--and roads that are part of the U.S. Route system.

There are very few exceptions to this even/odd numbering system. And it shouldn't surprise you to learn that there's a Web page devoted to explaining every exception.

If an Interstate Highway has three digits, look carefully at the first number. If a three-digit Interstate starts with an even number, then it means the road goes through or around a major metropolitan area. The much-discussed "inside the Beltway" political mentality is actually a reference to Interstate 495, a portion of I-95 that encircles the District of Columbia.

A three-digit Interstate Highway that begins with an odd number indicates that the road is a spur that leads directly to a city and does not rejoin the main interstate. Interstate Highways 380, 580 and 980, for example, are spurs off I-80 that lead to cities in the San Francisco Bay area. Once again, don't be surprised by the fact that there's a site devoted to discussing the quirks and characters of three-digit Interstate Highways. In fact, there's even a site devoted to Interstate 238, the only one that breaks the three-digit numbering conventions. To wit: There is no I-38 from which I-238 originates.

There's one more thing you should know about Interstate Highways. Those little, rectangular, roadside green-and-white mile markers also give directional clues. They are numbered consecutively, beginning at the south (on north-south Interstates) or the west (on east-west routes). Ascending mile markers on an east-west Interstate mean you are traveling east. Ascending mile markers on a north-south Interstate mean you're traveling north.

See, wasn't all that useful? I guarantee these tidbits will come in handy at least once this summer. And, as the folks at Esso used to say, Happy Motoring. At around $3.60 a gallon, the average nationwide price of gasoline is about a buck cheaper than it was last year. You can't say that about airfares ...