Types of 3dis

[empirestate]

Beyond the obvious loop vs. spur (even vs. odd), what categories of 3di (3-digit Interstate) can be said to exist? Start with odd and even as the two primary divisions, then subdivide. Some possible examples:

Bypass (I-481)
Beltway (I-285)
Loop from a parent into a nearby city (I-490 NY)
Loop within a city, alternate to the parent (I-405 CA)
Loop forming one side of a circumferential figure (I-444)

Spur towards a city (I-176)
Spur away from a city (I-990)
Double spur (I-540, at least formerly)
Downtown spur (I-375)
Long-distance branch route (I-135)
Wye (I-505)

And so on!

[adventurernumber1]

The "exit ramps" 

(I-189 in VT, I-175 & I-375 in FL, etc.)

[NE2]

orphan (I-278)
Jesus (I-238)

[admtrap]

orphan (I-278)
Jesus (I-238)

I disagree.  Jesus had Mary (which should be at least half of I-38, therefore... oh hell, it's I-19!)

[ajlynch91]

The "exit ramps" 

(I-189 in VT, I-175 & I-375 in FL, etc.)

I-381 fits very nicely into this category.

I-180 in Wyoming and I-587 in New York fit into the category "how the hell did they get interstate funding?"

[dfwmapper]

I-635 (KC), a bypass from one interstate to a different interstate.
I-635 (Dallas), a spur plus a bypass from one interstate to a different interstate and that bypass is also half of a 3/4 beltway.
I-345 (Dallas), a spur adjacent to downtown continuing as a non-Interstate freeway.

[jp the roadgeek]

In CT

I-291 and I-691: Connector routes between 2 2di's that could have been much more.
I-384: A remnant stub of a 2di killed by NIMBYs and environmentalists.
I-395: A long distance 3di through the middle of nowhere which changes numbers suddenly when it hits another 2di.
I-684:, A downgrading of a rerouted 2di.


Add I-395 in MD to the glorified exit ramp list. 

I-170 MD and I-895 NY: WTF? 3dis

[SteveG1988]

Incest 3DI: I-495/DC Beltway When a 3di and 2Di that were meant to be seperate ended up becoming one and the same.

[hotdogPi]

Are full beltways and half beltways considered different?

[ajlynch91]

Incest 3DI: I-495/DC Beltway When a 3di and 2Di that were meant to be seperate ended up becoming one and the same.

I can think of I-87/287 in New York, I-80/580 in San Francisco, and the aforementioned. Are there any other examples?

[froggie]

I don't think 87/287 were meant to be separate, so probably shouldn't count that.  I'd also use a more appropriate term than "incest".  Perhaps "conjoined"?

[Kacie Jane]

I don't think 87/287 were meant to be separate, so probably shouldn't count that.  I'd also use a more appropriate term than "incest".  Perhaps "conjoined"?

I'm too lazy to look up how long it lasted (or even if they were even signed as such) but I do know that New York submitted two different numbers to AASHO for each of the two independent portions.

[Pete from Boston]

I don't think 87/287 were meant to be separate, so probably shouldn't count that.  I'd also use a more appropriate term than "incest".  Perhaps "conjoined"?

Wasn't 87 originally supposed to cross over and come down on the east side of the Hudson?

[OCGuy81]

I-210 (CA)
I-110 (CA)

3-dis that continue as same numbered state routes.  I'd say 238, but I think that's better in the "orphan" category.

[ajlynch91]

I don't think 87/287 were meant to be separate, so probably shouldn't count that.  I'd also use a more appropriate term than "incest".  Perhaps "conjoined"?

I'm too lazy to look up how long it lasted (or even if they were even signed as such) but I do know that New York submitted two different numbers to AASHO for each of the two independent portions.

The Cross-Westchester Expressway was originally numbered I-487. New York for whatever reason wanted it to be a single route with the 287 in New Jersey, and it made sense to combine them over I-87 into one route.

[PHLBOS]

Wasn't 87 originally supposed to cross over and come down on the east side of the Hudson?

I-684 was originally planned to be I-87.

[froggie]

I'd heard this, that I-87 was intended on the east side of the Hudson farther north.  Curiously, though, this is not reflected in the Yellow Book.  It was afterwards that I-87 was routed along today's I-684, then eventually shifted back.

[Henry]

I can think of a few Chicagoland examples:

I-190: Spur into the main airport (O'Hare)
I-290: North/west bypass
I-294: Half-beltway around city
I-355: Two-way spur off I-55

[vdeane]

I don't think 87/287 were meant to be separate, so probably shouldn't count that.  I'd also use a more appropriate term than "incest".  Perhaps "conjoined"?

I'm too lazy to look up how long it lasted (or even if they were even signed as such) but I do know that New York submitted two different numbers to AASHO for each of the two independent portions.

The Cross-Westchester Expressway was originally numbered I-487. New York for whatever reason wanted it to be a single route with the 287 in New Jersey, and it made sense to combine them over I-87 into one route.

I think it's the reverse: NY wanted I-487 for the Cross-Westchester and I-287 for NJ, but the FHWA or AASHTO wanted them combined.  This is due to the thought difference in what I-287 is: to those of us from upstate NY, it is two separate entities not at all related, a bypass of the Cross-Bronx, and a bypass of the Turnpike.  To everyone else, however, it's a beltway around NYC.

[NE2]

Per Kurumi, AASHO approved separate 287 (west of Elmsford) and 487 (east of White Plains) in 1958. The two were combined in 1961.

[empirestate]

The "exit ramps" 

(I-189 in VT, I-175 & I-375 in FL, etc.)

I-381 fits very nicely into this category.

OK, what do we call this type? "Connector spur"? Is there any distinction between the downtown type (I-395 MD) and the outskirts type (I-115)?

I-635 (KC), a bypass from one interstate to a different interstate.
I-635 (Dallas), a spur plus a bypass from one interstate to a different interstate and that bypass is also half of a 3/4 beltway.
I-345 (Dallas), a spur adjacent to downtown continuing as a non-Interstate freeway.

I do think it's worth considering parentage in the classification. For example, a 3di off its parent is the default, a 3di off another 3di would be "second-order" or "sub-level", a 3di from a non-parent would be "unaffiliated", and so on. And of course there are hybrid cases.

In CT

I-291 and I-691: Connector routes between 2 2di's that could have been much more.
I-384: A remnant stub of a 2di killed by NIMBYs and environmentalists.
I-395: A long distance 3di through the middle of nowhere which changes numbers suddenly when it hits another 2di.
I-684:, A downgrading of a rerouted 2di.

Interesting histories aside, how can we categorize these according to their current state? I-691 seems a familiar type, a sort of branch/bypass; perhaps it's a "wye" like I-505?

I-291 is a bypass, but a certain kind that cuts a corner of a right-angle movement, rather than a half-loop that bypasses straight-thru traffic.

I-384 definitely looks like a "spur away from a city".

I-395 present an important case: a long-distance, intercity "spur", like I-380 IA, I-135, or I-476 PA (how do we reconcile the evenness of the latter?). I-395 does change numbers just shy of Worcester, but I think we can consider it as approaching that city.

I-684 is kind of another candidate for this category.

Are full beltways and half beltways considered different?

Yes, I think definitely so. What I also wonder is, are half-beltways and bypasses different? Can we find 3dis that are demonstrably one or the other, perhaps I-494/I-694, or I-481, or I-405 CA...?

I-210 (CA)
I-110 (CA)

3-dis that continue as same numbered state routes.  I'd say 238, but I think that's better in the "orphan" category.

I-210 seems like I-405, except that it's a right-angle bypass (albeit a very long one) instead of a straight-thru one (if I-405 is indeed a bypass at all). And both routes are definitely also "loops through a city", passing through interior areas of the city, but not the central city. I-278 is also this way (but of course, it's "unaffiliated").

I can think of a few Chicagoland examples:

I-190: Spur into the main airport (O'Hare)
I-290: North/west bypass
I-294: Half-beltway around city
I-355: Two-way spur off I-55

Airport spur is an important addition; there are definitely a few of those (I-380 CA, I-105 CA–but that's also a crosstown sort of route, more than simply an airport spur).

I-355 is interesting: it sure looks like a bypass, but the first digit tells us it's a spur, so...?

[PHLBOS]

I-395 present an important case: a long-distance, intercity "spur", like I-380 IA, I-135, or I-476 PA (how do we reconcile the evenness of the latter?). I-395 does change numbers just shy of Worcester, but I think we can consider it as approaching that city.

I-395 was originally CT/MA 52.  The redesignation to I-395 came about as a result of (mostly CT) trading in some unbuilt Interstate miles.  Since this was largely CT's doing; the option of extending I-290 south into CT and to I-95 was probably not considered an option.

Due to the highway going into MA; 395 was chosen because 195 was already being used in MA (& RI).

As previously mentioned, the reasoning behind PA 9 becoming an extension of I-476, as opposed to another I-x76 or even a I-x81, was rather obvious given that the Blue Route ended at the Turnpike (I-276)/NE Extension interchange.

[BrianP]

Loop from a parent into a nearby city (I-490 NY)

I would call that a business loop.  I-490 is similar to the I-95 business route for Fayetteville NC.  The difference being the latter is not a freeway for it's entire length.  But they serve the same purpose.  The main interstate does not directly serve the city.  So the business loop serves the city for the main route.

[Bickendan]

Oregon and Washington:
I-105 - Spur into a city
I-205 - Loop within a city/alternate to parent (and formally planned to be half of a circumferential)
I-305 (canceled) - Spur into a city
I-405 (both) - Loop within a city/alternate to parent
I-505 (canceled) - Spur away from a city
"I-605" - Loop around a city
I-705 - Spur into a city

[TheHighwayMan3561]

I-535: Spur into a city
I-394: Spur into a city
I-694: Bypass/alternate to parent

I-494 is hard for me to peg because it doesn't really neatly fit into any of the categories. It goes out of the way too much to be either a bypass or alternate to I-94, and also serves a number of major MSP suburbs on its own accord. It's basically its own animal with an x94 attached to it.