Longest distance on Interstate highways without having to “exit”?

[RustyK]

I was driving through Butte, MT today on I-90, specifically at the point where I-90 and I-15 split, when a question popped in my head after thinking about how in order to stay on 15, you must take an exit to do so.

The question: what is the longest one could be on interstate highways without having to "exit" ? (Once you reach a point that has already been traveled, you're done, so the answer cannot be infinity by getting on a beltway and looping forever  )

For example, this one is a little over 1715 miles:
1. Start in Seattle on I-90, heading east
2. Near Billings, MT, get on to I-94 (90 East exit 456 is itself - approx 824 miles)
3. Near Minneapolis/St.Paul, stay on I-694 (94 East exit 35B is itself - also approx 824 miles(!))
4. East of St. Paul, I-694 becomes I-494 at interchange with I-94 (approx 25 miles)
5. I-494 ends at junction with I-94/I-694 (approx. 43 miles)


I am going to post this and look at I-15 - if it never exits itself until Montana, maybe that stretch from start to Butte is longer than 90's Seattle to Billings stretch.
I also tried searching here and on the web in general and came up empty - probably more to do with how I phrased it than anything...

[RustyK]

Replying to myself as I looked at I-15: assuming it does not "self exit"  at any junction that is not another interstate, it's ~1300 miles from its start point to that self-exit near Butte, MT.

I-15 and I-215 in CA: no clear "exit"  marked for either roadway
I-15 near Vegas: 215 and 515 get the exit numbers
I-15 and I-80: 80 gets the exit number
I-15 and I-84: 84 gets the exit number

So... revising my example, now about 2280 miles:
1. Start I-15 North at junction of I-15 and I-8
2. Stay on I-90 when I-15 self-exits east of Butte, MT (approx 1160 miles)
3. Stay on roadway to I-94 when I-90 self-exits near Billings, MT (approx 229 miles)
4-6 are the same as 3-5 above (approx 892 total)

[Rothman]

This had to have been a topic already.

[RustyK]

I agree but I am having a heck of a time finding it.  I found one from a few years ago referencing self-exits, but it wasn't exactly what I was looking for

[kphoger]

|corco| says I-25 in its entirety.

[kramie13]

In Massachusetts, no Interstate highway exits itself.  You have I-95 coming close to doing so in Canton and Peabody, but the exit number is assigned to the ramp exiting 95.

But you get some oddities where "going straight" is "taking the exit" on I-95 south and I-93 south in Canton, as well as I-95 north in Peabody.  Massachusetts had yellow "LEFT" exit tabs on the highway signs approaching these interchanges but removed them recently, probably because they were creating confusion among drivers.

[Occidental Tourist]

If I'm understanding this correctly, one is exiting an interstate highway only if they are taking something clearly marked as an exit on that highway.

So, under these rules one could travel from San Ysidro (San Diego), CA, to Oakland, CA, to Sacramento, CA, to Salt Lake City, UT, and back to San Diego, CA, and never take a marked exit off the interstate.

The path would be I-5 north to 580 west near Vernalia, CA, to 80 east near Emeryville, CA, to the 15 south in SLC, and back along the 15 to San Diego at I-8.  Total mileage: 1,979 miles.

A couple of details: for the 5, there are no exits marked at the 5/10/101 interchange in East LA. Presumably if these ever get signed with exit tabs, the 5 would still not exit itself, but the 101 would exit left as an unnumbered exit and the 10 would exit right numbered as 134A.  For 80, there are no exits marked at the 80/50 split in West Sacramento, but, again, once these get exit tabs and numbers, 80 would be the thru route and 50 would be a left exit numbered 82.

Finally, the 5/580 split near Vernalia does not have any signed exits, and 580 (which is the left side of the split) has an internally assigned proposed exit number of 446 from the 5.  Once 580 is signed as a left exit by Caltrans, then this route is no longer good under the rules of this exercise as you would have to stay right on the 5 at this point to avoid "exiting"  the freeway. 

Under that scenario, if you started from the 580/5 split instead of San Ysidro, followed 580 to the Bay, 80 east on to SLC, and again ended on the 15 south in San Diego, total mileage would drop to 1,333.