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The Interstate


Here is another post from my Dad! Thank you, Dad!

I really enjoyed reading all of the comments on my last post! Thank you! Yes, we do go through Columbus Ohio. On Thursday morning around 7:00AM and then again Friday afternoon around 4:00PM. I will be happy to answer any other questions you have. For now I thought I would write about the Interstate.

Most people have driven the Interstate system at one time or another, but I wonder how many people really understand the Interstate system? To be a successful truck driver, understanding the Interstate system is a requirement.

When I worked for a year at our Fontana (California) Terminal, I was privileged to conduct a Map class as part of the two-day Orientation program. Even though I had driven a truck for more than ten years before that, I found I didn’t fully understand the Interstate system. There were several things I learned when I taught the Map class for the first time.

The Interstate as we know it today was built during the 1960’s, but the planning started with the Eisenhower administration during the 1950’s. However, the need for a nationwide road system was realized as far back as World War I, when then-Lieutenant Dwight D. Eisenhower was assigned to lead a convoy of war machinery and supplies from New York to San Francisco in 1919.

Eisenhower was embarrassed to find that the powerful United States of America had no road system in place to move military equipment from one side of our country to the other. Sure, there were roads linking one city to another but that was the extent of the planning! No one had considered the need to build a single road from one side of the country to the other.

Can you imagine the frustration Eisenhower felt when he looked at the zigzag route he would have to take just to get from one city to another? In 1919 there was probably little in the way of road signs, or even printed maps showing where roads would lead. The cross-country trip took over a month! Eisenhower saw this as a serious national security issue and vowed if he was ever in a position of influence, he would do something about it.

winter 2007 and blowing snow 034

When President Eisenhower took office in 1953, the railroad system was well-established. Moving military equipment around by train had been fine when the only alternative was travel by horse, but Eisenhower recognized that modern trucks and cars would allow much faster movement of men and equipment than the railroads if only there were a better system of highways. One of Eisenhower’s first tasks as President was to create the committees that would oversee the creation of a national road system capable of moving men and equipment quickly and efficiently around the country.

It was a monumental task, designing a road system that would not only lead from a major city to another major city but would be able to convey a vehicle from New York to San Francisco or San Antonio to Minneapolis. Nobody envisioned the Interstate would become the backbone of our economy, moving goods from factories to local stores. The number of trucks on the Interstate today is almost mind-boggling.

One of Eisenhower’s problems as he made his way across America with that military convoy was that there was no consistent highway numbering system. When a motorist today drives on, say, I-80 they know that they could go all the way from San Francisco to New York, and all they have to do is stay on I-80. In 1919, that was not the case.

Which is why one of the most important features of our Interstates is the numbering system. It was recognized early on that a numbering system must be well-designed in order to have consistency throughout the country. I am amazed at the insight the planners had when they planned it out. If you know the system, it will help you travel around this country.

All cross-country Interstates are numbered with a single digit (I-5) or two digits (I-80). If the Interstate has three digits the highway is always associated with a metropolitan area, like I-270 around Columbus, Ohio; I-635 around Dallas; or the I-695 around Baltimore. (More about that later.)

All East/West Interstates are even numbers: I-40, I-70, I-80, etc. All North/South interstates are odd numbers: I-15, I-35, I-95. There are a few diagonal Interstates like I-74 from Walcott, Iowa, to Cincinnati. The planners judged, I guess, that these highways were more East/West than North/South so they gave them even numbers.

The East/West (even-numbered) Interstates start with the lowest number in the south and get higher as you go North: I-10 from Jacksonville, Florida, to Los Angeles; I-20 through Texas; I-40 through Oklahoma City; I-70 through Denver and Kansas City; and I-80, which starts at San Francisco and ends in New York, passing through Chicago, Omaha, and Salt Lake City. North of that we have I-90 from Seattle to Boston, and I-94 from just east of Billings, Montana, to Detroit, Michigan. North/South (odd-numbered) Interstates start with the lowest number in the west (I-5 from San Diego to Blaine, Washington, on the U.S.-Canada border) and get higher as you go east (I-95 from Maine to Florida).

Now let’s talk a little about the three-digit Interstates. As I mentioned earlier, a three-digit Interstate will always be associated with a major city. When an Interstate arrives at a major city, almost always there will be a loop around the city. All loops start with an even number. When there is a section of Interstate that connects a suburb with the city center, that is called a spur. Spurs always start with an odd number. The last two digits of the three-digit Interstate number are determined by the cross-country Interstate the loop or spur intersects with. I-70 runs though Columbus, Ohio, so the loop around Columbus is called I-270.

Atlanta is an interesting city. There are three major Interstates intersecting Atlanta: I-20 runs East/West through the city; I-75 runs Northwest/Southeast; and I-85 runs Southwest/Northeast. The planners arbitrarily called the loop I-285.

Mile markers are another interesting feature of the Interstate. Did you know that federal regulations require Interstate exit numbers match the nearest mile marker? Until a few years ago, Pennsylvania and Georgia and maybe a few other states numbered their exits in order. The first exit was Exit 1, the second exit was Exit 2, etc. California is the last state to comply with federal regulations requiring exits to have an exit number that reflects the mile marker. Except that California doesn’t have mile markers! Oh, we have Mickey-Mouse county mile markers that number from one county to the next county, but that is totally confusing for even a seasoned truck driver. All the other states have mile-marker exit numbers. We all wonder if California will ever have actual mile markers.

Interstste through Virgin River Gorge Arizona

Next time you drive on an Interstate, you might know a little bit more about it. I hope this has been informative and not boring!


  • Pictou

    A word puzzle: Leaving work, I get on I-64 east at exit 33, take I-95 north to I-295, connecting again with I-64 east. Continue 1-64 east to exit 234 to go home. Where do I live?

  • Sonja

    That was absolutely fascinating! I learned about the even/East-West and odd/North-South connection in high school in Germany (in my English classes), but the loop & spur thing was news to me. Thanks!

  • Nat

    Completely fascinating.

    I’m Canadian, we were driving from Boston to Ottawa. And The Man told me about Eisenhower and I totally did not believe him. Turns out he was not talking out of his ass… what do you know.

  • The Chatty Housewife

    That is so interesting! Thanks for sharing. My husband always clues people into the whole mile marker/exit name idea. It allows you to see how close you are to a certain exit by watching for mile markers. I had no clue there aren’t true mile markers in California.

    You mentioned my home- Blaine, WA!

  • LIRP

    This is in no way boring. It has always been an interesting subject of the secret lives of a truck driver. How you stay alert and not bored. What you do for food, if you have any good places to stop or stop at the same places each time? Stories that IM sure we would be super surprised to hear. Also, the tips in which you would recommend to avoid problems on the highway or in bad weather when near a truck. What would make it easier for the truck driver… signals you can give… all that stuff. You should write a book. Thanks for the guest post :)

  • Lady S

    Thanks for the information, “Dad”. I knew the N-S/E-W numbers thing, but most of the rest of it was new to me. I just have one question. You say that CA was the last state to comply with the mile marker rule, but I drive I-91 all the time and Vermont, Massachusetts and Connecticut are numbered in order, not by miles (the southern most exit in Vermont is 1 and is at mile 7, exit 2 is at mile 9). I think this is also the case on I-93 in NH and I-89 in VT.

  • bethany

    cool, thanks for that! I found the PA exits annoying when i lived there, so much nicer to know how far you had to go w/out looking it up! Happy driving :).

  • karen

    California isn’t last to comply with that milepost/exit number system. I-90 in New York (“the 90” to Buffalo natives) still has numerical exits!

  • Sara

    This is great! Hey, what do you know about the interstate system in CT? Our friend who lives there says the road system was designed around the old cow paths. When we went to visit, we found the exit systems (as well as the driving) to be quite crazy. Often there would be an entrance on the left and then an immediate interchange on the right! We live in Oregon where where the interstate basically makes sense, so we were thrown for a (literal) loop a few times out there. All the best for your travels!

  • gretchen w

    I’m so glad you wrote another post- and it all made more sense to me because you used some Columbus references. Thanks! Unfortunately I am usually on 70 and 670 (another part of the loop) closer to rush hours- I’m sure you guys try to avoid those. But I bet I will see you some day- I will keep an eye out! Drive safely–

  • cynthea

    And now I’m looking forward to your expose on state hwys and rtes. Those must have a method to the madness, too.

  • nancy

    loved this info. I am glad that I now know about California and the no mile markers (or often exit numbers at all much less corresponding to mile). It has been something that has been making me crazy since I moved here two years ago.

  • K

    I knew a lot of this from my Dad but I find it interesting that different areas have similar interstate areas. I live right off I-270 but nowhere near colmbus. Also, 270 in md has a spur to 495 and it starts with an even number. 495 is the loop around dc.

  • BeachMama

    Thanks Tom! Although I have always known of your Interstate system, I didn’t know how or why it was started. Very, very cool. Our Canadian system is so simple in comparison, but really we have so few people and Provinces compared to the US. Great job explaining, now if only I could take one Interstate from Ottawa to Delaware and not have to loop around Philidelphia, we always seem to take a wrong turn, either on the way there or the way back. Phili is a lovely city though..

  • Victoria

    That was so cool! (Even for me, as a Canadian!) I loved knowing about the East/West, North/South thing so that if I’m in the States and want to get back “home” I’ll know what name of a highway to take :)

  • Annabanana

    That snow blowing photo is way to familiar to me, yeck!
    My father in law is a truck driver and he did norther hauls for years over ice bridges and snow highways. (From Edmonton to The Northwest Territories)
    Very interesting post! Thank you! I truthfully knew nothing about the history of the interstates. I would say it is because I am Canadian but that is no excuse!

  • Barb

    Boring? Are you kidding? I find it really interesting. Hey, I bet you know the answer to this question: Why do people from California (and maybe other states) put the word “the” in front of the numbers of the highway, i.e. “the 5”? We don’t do that in the Midwest. We call it I-75 or I-96, but never “the 75” or “the 96”. Any ideas on that?

  • Chrystal

    This is so cool and so very true….My husband is an OTR truck driver and we used to travel the States until we found that we were expecting our first child…The Interstate system is very interesting and more complex than most people realize…And yes poor ol California is slacking with the mile markers and if you are in a truck that sucks! Thanks for sharing your knoledge!!!

  • Erin

    What a great lesson! Thanks for sharing your Interstate knowledge with us! You helped me put the final piece of the New York highway system numbers into place.

    Y’see, we have consecutively numbered highways in NY, starting with 190, 290 & 990 in Buffalo, 390, 490 & 590 in Rochester, 690 & 790 in Syracuse and 890 in Albany.

    Anyone wanna guess what the New York State Thruway’s number is? 90!

  • Mrs. Wilson

    Not boring at all, actually quite interesting. I am a Canadian, but I find the US intriguing. Now, when my husband and I visit EVERY SINGLE FOOTBALL FIELD THE US HAS TO OFFER, I will be able to know where we’re going just a bit easier. Thanks!!

  • cc


    I lived in Illinois for four years, we always said take I-whatever to whatever. We moved back to California and now I say take the 10 to the 210 to the 215 to the 15. I don’t know why we do it, we just do.

  • Jamie W.

    That is very cool to know. I had always wondered why Atlanta changed their exit numbers since I was in high school, and now I know!

    Is it true that the Interstate system was designed with a requirement for every few miles to be straight enough to land airplanes? I’ve heard that before but didn’t know if it was an urban legend…