Interstate designations that maintain the through movement

[briantroutman]

I was wondering are there any other such US designations that do not make any turns like US 192 in its entire run?

This other thread got me thinking–what Interstate designations maintain the through movement for their entire length? In other words, the grading and markings are such that, if you went "straight" at every possibly interchange, you would stay on the same Interstate. And better yet, what are the longest of these?

Many long-distance designations–like I-90 exiting the Berkshire Connector near Albany and I-70 exiting the PA Turnpike at New Stanton–obviously wouldn't qualify. There's definitely some gray area involving 50/50 splits and left exits. I'd argue that I-81 near Lebanon, PA is graded as if I-78 was the through movement and therefore wouldn't qualify. And at Alexandria, I'd say I-395 looks  and feels more like the through movement–although I-95 is out of the running for other obvious reasons.

[agentsteel53]

does the western I-84 manage it?  I forget what it looks like offhand in Portland, but I believe it survives both ends of the 15/84 multiplex.

I-27, probably.

I-29, maybe.

[Kacie Jane]

does the western I-84 manage it?  I forget what it looks like offhand in Portland, but I believe it survives both ends of the 15/84 multiplex.

Nope. Going straight puts you on the oft-maligned I-86.

[agentsteel53]

it's not a 50/50 split?  or does that not count?

[Kacie Jane]

Both lanes eastbound go "through" to I-86.  To stay on I-84, it's a single-lane exit.

ETA: Also, the northern I-15 split, yes, but not the southern one.  It's not a 50/50 split, and you definitely have to exit right as opposed to going straight to stay on I-84.

[hbelkins]

I-99?

[agentsteel53]

damn ... I-15 makes it all the way to I-90 from San Diego with only a few 50/50 splits (215 north end in SoCal, 84/15 north split in Utah) before 90 mercilessly eats it and spits it out again.

[briantroutman]

it's not a 50/50 split?  or does that not count?

Like I said, it's a gray area. 50/50 splits are probably OK because either motion (or neither of them) could be argued to be the through movement. But it does make for less of a "clean" answer.

[corco]

What about I-25? I think that one does.

[Molandfreak]

What about I-25? I think that one does.

Correct!



I-81 only has two 50/50 splits northbound. Four southbound. Pretty amazing for a route that long.

I-878

[SteveG1988]

I-195 in NJ, I-276 in PA, I476 as well

[NE2]

possibly i-76 (east)

Hell no. It turns off at Youngstown and Valley Forge.

[corco]

I-76 west does though, as does I-82, I-86, I-17, I-8, and I-19

[Thing 342]

I-16, I think.

[hotdogPi]

I-495 in Massachusetts (one of the long 3dis)

I-91 going south (going north, I-391 in MA goes straight)

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I-16, I think.

Yes, I-16.

I-88 in New York, but that's just because it doesn't have any interstates in the middle.

I-89.

I-2. 

The junction with MA 3 on I-93 messes it up.

[Revive 755]

I-29, maybe.

I'm going to lean towards no for southbound, given the left exit for IA 192 on the north side of Council Bluffs:
https://maps.google.com/maps?q=council+bluffs,+ia&hl=en&ll=41.287854,-95.867414&spn=0.004828,0.008256&sll=41.287461,-95.866243&sspn=0.003414,0.008256&hnear=Council+Bluffs,+Pottawattamie,+Iowa&t=k&z=18&layer=c&cbll=41.287854,-95.867414&panoid=SUpKbVuxMTY6WbiIpbogVg&cbp=12,186.67,,0,-1.75

Northbound appears to meet the criteria, but this may change with the rebuild of joint section with I-80.

[Duke87]

Going down the list, everything longer than I-25 is a no. So, that's the winner.

So, counter question: what's the shortest interstate that doesn't maintain the through movement?

Depending on how we interpret traffic circles the answer might be I-587. If we don't count that, then it's I-790.

[Alps]

I-99?

No, US 322 is the through movement at State College.

[Mr_Northside]

I-99?

No, US 322 is the through movement at State College.

I'd have to disagree... having driving thru it a couple of times, the interchange was set up to make I-99 clearly the thru movement. (even though, historically, US-322 was the through movement.)

I'd argue that I-81 near Lebanon, PA is graded as if I-78 was the through movement and therefore wouldn't qualify.

I suppose it could be an arguable point... though I'd firmly side with I-81 being the through movement.  Mostly cause of the striping & signage.

[TEG24601]

does the western I-84 manage it?  I forget what it looks like offhand in Portland, but I believe it survives both ends of the 15/84 multiplex.

Nope. Going straight puts you on the oft-maligned I-86.

Also, technically when heading West, if you don't exit at I-205, you end up on 205.


I-90 actually looses it at Billings, MT, as I-94 is the mainline.


I believe that I-96 in Michigan qualifies, as the mainline around Lansing, in both directions is I-96, and at I-275, the primary/majority of the lanes exiting are I-96, whereas I-275 veers off, and is the smaller of the two exits.


It might be easier to think of non-3di routes within a particular state.

[kj3400]

I-97*. 


*though at the beltway interchange, it's not clear which way is the mainline.

[froggie]

I-91 going south (going north, I-391 in MA goes straight)

I-91 is the through movement here...just because I-391 in this case "goes straight" doesn't mean it's the through movement, as the I-91 mainline itself is in the middle of a curve.  Plus, 391 is signed as an exit.

So I-91 counts.  And since it hasn't been mentioned yet, I believe I-79 does as well, depending on how one defines the 79/279 split in Franklin Park (I'd call it a 50/50).

[CNGL-Leudimin]

I-4

I-238

However, CA I-580 apparently doesn't qualify, as going westbound and missing the "exit" in Castro Valley puts you on 238.

[empirestate]

So, counter question: what's the shortest interstate that doesn't maintain the through movement?

Depending on how we interpret traffic circles the answer might be I-587. If we don't count that, then it's I-790.

I am not convinced I-587 even goes through the traffic circle. NYSDOT says it doesn't exist anywhere NY 28 isn't overlapping.

[hbelkins]

And since it hasn't been mentioned yet, I believe I-79 does as well, depending on how one defines the 79/279 split in Franklin Park (I'd call it a 50/50).

Wouldn't the two I-70 intersections disqualify it?

But I-68 would certainly count.