Interstate numbering explained: (or why there is no I-50 or I-60)

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Open Road

"Eliza, why is there no I-50/60, why?" someone once asked (though I suspect he knew the answer already).

In 7th grade I wrote a report about the design, history, and numbering of the Interstate system. In the spirit of recycling knowledge, here are the highlights as I recall them:

The Federal Highway Administration's Route Log and Finder List has more information.

An open question (as far as I know), in the spirit of The Traveling Salesman Problem, is: what route you would need to take on a road trip to drive at least one mile on each numbered Interstate (either with or without including beltroutes) in the 48 contiguous states to minimize distance traveled and/or time.

In Utah the quickest way I can think of to go at least a mile on each Interstate would be to begin at Cove Fort near the I-70/I-15 junction. Travel on I-70 and go north on I-15 at the junction. Continue until you get to the southern I-215 interchange in Salt Lake County and take it to I-80. Go up into the canyons until you reach the I-84 junction near Echo.

(Interstate 50 is also the name of an interesting artistic photo collection.)

—Michael A. Cleverly


John Cowan: [ mail | www | link ]

All those rules and a lot more (like, why is there an I-238 when there is no I-38, and what on Earth is it doing in California?) explained at .

The U.S. highway numbers are less systematic, but they do have the rules north-south odd and east-west even, though they are numbered from east to west and north to south respectively (U.S. 1 and U.S. 2 intersect in Bangor, Maine).

Tue, 19 Jul 2005, 11:36

Louis Zirkel: [ mail | www | link ]

Paula and I recently watched a History Channel program about this very subject and I remember part of the rational behind the number scheme, and more importantly the direction (west to east ascending, north to south descending) was to avoid as many clashes (i.e. the US50/US60 vs I-50/I60) as possible.

Tue, 19 Jul 2005, 13:12

Nadine Lagarde: [ mail | www | link ]

How many cities in the U.S. are there that have two interstates that cross each other?

How many cities in the U.S are there that have three interstates that cross each other?

Thank you

Fri, 22 May 2015, 17:59

Derek Mohr: [ mail | www | link ]

None all interstates turn into other interstates they don't intersect. They have bypasses that "bypass" large cities. 275 bypasses Tampa for example. So I don't believe that there are any cities where interstates intersect. If I'm wrong please let me know. I'd be interested to find out if my thesis is correct. Thank you.

Wed, 11 May 2016, 01:12

Isaac Levy: [ mail | www | link ]

Seriously Derek, there are plenty of Interstates that intersect inside of major cities in the US. For example, I-5 and I-10 intersect near Downtown Los Angeles. I-30 and I-35W interects in Downtown Fort Worth. The list goes on and on, but plenty of mainline Interstates intersect in major cities.

Fri, 17 Jun 2016, 20:34

Isaac Levy: [ mail | www | link ]

Derek, there are plenty of Interstates that intersect inside of major cities in the US. For example, I-5 and I-10 intersect near Downtown Los Angeles. I-30 and I-35W interects in Downtown Fort Worth. The list goes on and on, but plenty of mainline Interstates intersect in major cities. There are bypasses, such as I-610 in Houston and I-495 around the Washington DC Metropolitan area, among many others, but those are used to reach and connect the outskirts of major cities and sometimes to divert 18 Wheelers and other commercial vehicles away from the downtown area of cities to lessen traffic. Some cities and metropolitan areas are large enough to require multiple loops & secondary interstates to handle traffic, but that's another story...disregard my first comment, sorry for coming off harsh

Fri, 17 Jun 2016, 20:43

Ash: [ mail | www | link ]

Which interstate has the best lot lizards at the rest stops?

Sun, 27 Nov 2016, 20:47

PFunk: [ mail | www | link ]

I have a notebook somewhere where I answered that exact question. I scrolled google maps and found every interstate intersection in cities. I think it was something like 92, but at the time I didn't count auxiliary highways. I should recount that...

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