Numbering of 3di interstates ... why not use the lowest digit available?

[3467]

I think I-255was numbered like a bypass and then extended and for some crazy reason it hasnt been given an interstate degination all the way even though it is more like a spur.
Illinois did want to use x74 numbers for the Quad Cities . The numbering fight with Iowa is old(my current idea is to extend 88 to Iowa and 188 to Monmouth) This  brings me to 174, IDOT did try to get that for US 34 Galesburg-Monmouth

[TheStranger]

Like IL-255, I guess.

Like VA-381

More examples:

NY 890, NY 690, NY 590, NY 390, NY 787, NY 481

Route 110 in California

PA 283

[The High Plains Traveler]

BY 1960, Minnesota renumbered its existing state highways that duplicated the interstate numbers: 35, 90, 94, in each case by appending "1". It did not use existing three-digit state route numbers, though for 3di interstates; I-494 was established instead of 294, which was an already existing very minor route serving a state facility in Willmar. And, a proposed route north of downtown Minneapolis that was ultimately shelved was designated I-335 instead of 135, even though that route was itself created in place of old state route 35. That is why the lowest odd prefix I-x35 is 535.

[empirestate]

This would explain a lot.  I never thought of it, but there is a pattern of the way the first numbers are selected as I can see in New York for I-90 spurs going from 1 to 8 from West to East, and then I-990 was added later so its out of the grid.

Then for I-78 (if it had gone through Manhattan, Brooklyn, and Queens) had I-278 to the west, then I-478, I- 678, and finally I-878 all from West to east just like the mileage and exit numbering.

I seem to recall a related thread about which states number their 3dis in geographical sequence, and NY is obviously one of them. Although it's most apparent with the x90s, I think the same practice is seen applied with x87s: I-587 and I-787 are where you'd expect them to be, allowing for 187 and 387 farther downstate (regardless of whether either of those were actually proposed). I-481 was originally to be numbered 281, but it was changed perhaps not so much because of nearby NY 281 (as state routes have a tendency to be renumbered in favor of duplicate Interstate numbers) but to allow for a possible I-281 in Binghamton.

[A.J. Bertin]

I seem to recall a related thread about which states number their 3dis in geographical sequence, and NY is obviously one of them.

Michigan kinda does this with the x96's... from west to east, you have I-196, then the hidden I-296, then I-496, then I-696.

[Ace10]

Not sure if Louisiana has been mentioned yet, but I-x10s in Louisiana seem to be in order from west to east:

I-210 in Lake Charles
I-110 in Baton Rouge
I-310 west of New Orleans
I-610 in New Orleans
I-510 east of New Orleans

It works if you think of the spurs and loops as two separate lists. This could provide an I-410 in Baton Rouge, and even an I-810 in New Orleans or Slidell.

This also doesn't take into account the hidden I-910 on the Crescent City Connection/Pontchartrain Expressway/Westbank Expressway, but perhaps the number "910" was picked because it was intended to be hidden and wouldn't create a numbering gap somewhere if this is what Louisiana was going for?

[DandyDan]

As for Nebraska, the only reason there is not an I-280 is because what is now I-680 was supposed to go into Iowa, where there already was an I-280.  That leaves unexplained why what is now the North Freeway (currently US 75) in Omaha was going to be I-580.  They must have thought the North Freeway would go into Iowa as well, negating the ability to name it I-380.  (FWIW, I think that would be a reasonable freeway construction, not that it's going to happen anytime soon.)

In Iowa, the mystery Interstate designation is I-380.  Obviously, at least to me, it should be I-180, although Illinois and Nebraska have those as well.  But the thing about Iowa is, at least by looking at Jason Hancock's Iowa highway website, IA 129, IA 235, and IA 280 all existed (as did IA 380) before the numbers were reassigned to the current interstates (presumably, so did 29, 35, 74 and 80, but I didn't look those up).  So why they didn't change it to 180 is presumably to avoid confusion with its neighboring states, although I'm not sure how one can be confused.

[mjb2002]

It seems like there are many occasions where 3-digit interstates are numbered a bit strangely. The DOTs (or whatever agency is responsible for selecting highway numbers) have made some strange choices. For the 3-digit interstate highways, either four digits (2, 4, 6, or 8 - in the case of loops) or five digits (1, 3, 5, 7, or 9 - in the case of spurs) are available. There are many occasions where I higher digit was selected when lower digits are available.

Here are a few examples I've noticed:

I-375 in Detroit, MI - why not I-175?
I-516 in Savannah, GA - why not I-116?
I-675 outside Atlanta, GA - why not I-475?
I-794 in Milwaukee, WI - why not I-594?
I-459 in Birmingham, AL - why not I-259?
I-520 in Augusta, GA - why not I-120?
I-820 in Fort Worth, TX - why not I-620?
I-530 in Arkansas - why not I-130?
I-684 in New York and Connecticut - why not I-284?
I-691 in Connecticut - why not I-491?

These are just some examples of what I'm talking about. I don't know why this bothers me, but it just does. LOL

I can answer the I-520 question. The reason why there is no I-120 is because the BOBBY JONES EXPWY now extends into North Augusta, SC - and there is an SC 120 in the state in Sumter County. Either GDOT or SCDOT, or both, want to avoid using the same route numbers for Interstate and State Routes as much as possible. Hence, why there are only a handful of highways that have the same number for Interstate and State Routes in SC. I-126 in Columbia and BELVEDERE-CLEARWATER RD (SC 126) in Aiken County, as well as I-20 and SC 20, are rarities.

[NE2]

I can answer the I-520 question. The reason why there is no I-120 is because the BOBBY JONES EXPWY now extends into North Augusta, SC - and there is an SC 120 in the state in Sumter County.

??? I-520 was only in Georgia for a long time.

[Mapmikey]

I can answer the I-520 question. The reason why there is no I-120 is because the BOBBY JONES EXPWY now extends into North Augusta, SC - and there is an SC 120 in the state in Sumter County. Either GDOT or SCDOT, or both, want to avoid using the same route numbers for Interstate and State Routes as much as possible. Hence, why there are only a handful of highways that have the same number for Interstate and State Routes in SC. I-126 in Columbia and BELVEDERE-CLEARWATER RD (SC 126) in Aiken County, as well as I-20 and SC 20, are rarities.

South Carolina does not care about interstate routes having numbers already in the state highway system. They only changed SC 77 and SC 85 because North Carolina had this policy.

South Carolina retains SC 20, SC 126, SC 185, SC 385

SC 26, SC 95 and SC 526 were renumbered/retired before the interstate era.  SC 73 appears to also have been recently decommissioned (not renumbered).

Additionally, Georgia has coincidental state route designations for all of its 2di numbers and I-185 and has a prominent GA 520 which came years after I-520 was in place.

It seems to me that the 516 and 520 designations fit the geography dynamic where 1xx and 3xx are reserved for potential use further west on those interstates.



Mapmikey

[apeman33]

I've always wondered why the beltway around Topeka was numbered I-470 instead of I-270. I always thought it odd especially considering there's an I-470 in the Kansas City area. But Topeka's I-470 meets its parent at both ends while Kansas City's only meets it at its farthest east point, so maybe confusion isn't likely.

Richie, you ever heard anything about why Kansas' I-470 is numbered as it is?

[national highway 1]

But that's why San Antonio is I-410 and Houston is I-610, I think, so that El Paso could have I-210 if ever necessary.

I-210 would be a potential number for Loop 375 in El Paso if it were upgraded to interstate standards.

This also doesn't take into account the hidden I-910 on the Crescent City Connection/Pontchartrain Expressway/Westbank Expressway, but perhaps the number "910" was picked because it was intended to be hidden and wouldn't create a numbering gap somewhere if this is what Louisiana was going for?

It's plausible whether I-910 was picked to align with US 90 BUS.

[Alex]

Another example... why is I-474 in Illinois (around Peoria) not I-274?

Peoria has 474 because 274 was reserved for the Quad Cities. On paper Interstate 274 was intended for the current stretch of I-80 from I-74's west end to the I-74/280 junction to the southeast of Quad Cities. In this plan I-74 and 80 shared pavement through the heart of the QC. AASHO replaced I-274 with a realigned I-80 on November 10, 1958.

[OCGuy81]

Wisconsin comes to mind with this thread.  Why jump to 894 and 794 in the Milwaukee area, when 1-6 were available as prefixes for 94 statewide.

[Henry]

Here's another subject to ponder: I-30.

I-430, I-530 and I-630 exist (as will I-130 in a few years), but I-230 and I-330 do not. One has to wonder why this is so.

[bassoon1986]

Here's another subject to ponder: I-30.

I-430, I-530 and I-630 exist (as will I-130 in a few years), but I-230 and I-330 do not. One has to wonder why this is so.

I'm pretty sure 130 was in the books as a potential spur for Texarkana on AR 245 before more was completed on I-49. Then they realized that 49 would use most of that roadway. I think Kurumi's site may attest to this.

[triplemultiplex]

Wisconsin comes to mind with this thread.  Why jump to 894 and 794 in the Milwaukee area, when 1-6 were available as prefixes for 94 statewide.

My theory from upthread:

The I-94 spurs in Milwaukee seem to have been chosen from the high end to distinguish them from sorta nearby Chicago and it's I-294 and then-proposed I-494.

With 794, I have noticed that if there was a spur from I-94 into Kenosha, another into Racine and interstate status for MKE's airport spur, one would have sequential odd spurs increasing south to north.  At some point, there were east-west freeways proposed between I-94 and the once-proposed Lake Freeway in both Racine and Kenosha.

Or if one was numbering spurs of I-94 west to east, Milwaukee would be near the west end and given higher x94's.

[pianocello]

As for Nebraska, the only reason there is not an I-280 is because what is now I-680 was supposed to go into Iowa, where there already was an I-280.

That, and that the only 3dis in Omaha would cross into Iowa.

That leaves unexplained why what is now the North Freeway (currently US 75) in Omaha was going to be I-580.  They must have thought the North Freeway would go into Iowa as well, negating the ability to name it I-380.  (FWIW, I think that would be a reasonable freeway construction, not that it's going to happen anytime soon.)

I think (and I have no legitimate basis for saying this) that maybe 5 was used because it was close to the other two 3di numbers in Omaha.

[Henry]

As for Nebraska, the only reason there is not an I-280 is because what is now I-680 was supposed to go into Iowa, where there already was an I-280.

That, and that the only 3dis in Omaha would cross into Iowa.

That leaves unexplained why what is now the North Freeway (currently US 75) in Omaha was going to be I-580.  They must have thought the North Freeway would go into Iowa as well, negating the ability to name it I-380.  (FWIW, I think that would be a reasonable freeway construction, not that it's going to happen anytime soon.)

I think (and I have no legitimate basis for saying this) that maybe 5 was used because it was close to the other two 3di numbers in Omaha.

That, and also because I-180 in Lincoln and I-380 in Cedar Rapids already existed at the time.

[Urban Prairie Schooner]

Not sure if Louisiana has been mentioned yet, but I-x10s in Louisiana seem to be in order from west to east:

I-210 in Lake Charles
I-110 in Baton Rouge
I-310 west of New Orleans
I-610 in New Orleans
I-510 east of New Orleans

It works if you think of the spurs and loops as two separate lists. This could provide an I-410 in Baton Rouge, and even an I-810 in New Orleans or Slidell.

This also doesn't take into account the hidden I-910 on the Crescent City Connection/Pontchartrain Expressway/Westbank Expressway, but perhaps the number "910" was picked because it was intended to be hidden and wouldn't create a numbering gap somewhere if this is what Louisiana was going for?

I-410 was originally planned for Baton Rouge; late 1950s state highway maps show current I-110 as 410.

[empirestate]

I suppose the other way to ask the question is, why would you use the lowest number available? Besides satisfying a rather abstract desire to start from the beginning, it has the effect of numbering them chronologically by their construction date, which seems less useful than having a geographic sequence or some other rationale. Imagine if exits were given the next available number at the time they're opened; you'd have a pretty meaningless system! (And indeed, that's one of the complaints I most often hear about sequential exit numbering: that it leaves no room in the sequence for added interchanges.)

[Roadsguy]

Do what most states (or at least the NJTA) do:

Exit 8, (drive, drive, drive...) newer, unrelated Exit 8A, (drive, drive, drive...) Exit 9...

[Scott5114]

Most people don't even realize that I-240 and I-40 are "related". I doubt it would even cross their mind that the numbers went in a particular order (the 2dis being in order never seems to occur to non-roadgeeks unless I point it out).

[hbelkins]

It's not silly.  Duplicating route numbers creates confusion giving directions, reporting location when calling 911, discussing highways among officials and legislators, creating reports like statistics for every route in a state, etc., etc.

When you duplicate route numbers across systems, you get silliness like this:

[kkt]

I suppose the other way to ask the question is, why would you use the lowest number available? Besides satisfying a rather abstract desire to start from the beginning, it has the effect of numbering them chronologically by their construction date, which seems less useful than having a geographic sequence or some other rationale. Imagine if exits were given the next available number at the time they're opened; you'd have a pretty meaningless system! (And indeed, that's one of the complaints I most often hear about sequential exit numbering: that it leaves no room in the sequence for added interchanges.)

Exactly.

Though growing up in California we were lucky when any 3di number was available for a spur or loop off its 2di, let alone having them be in a pattern of any sort.