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

[A.J. Bertin]

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

[Big John]

For the I-675, there is a I-475 that bypasses Macon, GA.  But there is no I-275 in Georgia.

I believe these are at higher mile markers so the lower numbers were bypassed in case of another 3DI was built/commissioned at a lower mile marker of the 2DI.

[corco]

Wasn't the idea in Texas that the loop numbers would increase as you move east across the state? So, Midland/Odessa, Abilene, and one other city would have those lower numbers if ever built. I'm not sure where I heard that so I could be full of baloney.

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.

[dfilpus]

In NC, the state has a plan for future Interstates all over the state, which had numbers assigned to proposed routes. Now some of those Interstates are being created, the original numbers are being used. That is why, when US-117 was converted to an Interstate, it got the number I-795. All of the lower odd numbers have been reserved for other future Interstate spurs off of I-95. I-195 was renumbered to I-295. If I recall correctly, I-395 and I-595 were reserved for US-64 and US-264, east of I-95. Greensboro has two future interstates that are now signed "Future" as I-840 and I-785. These numbers go back to the original plan.

[Takumi]

Virginia seems to just not want to disrupt its numbering system anymore. The last Virginia state route renumbered for a 3di was VA 195 (now 186) in the 1970s. Since then I-564 was created with VA 164 and 364 already extant. I-785 will just be an extension of NC's, and the proposed I-895 (now VA 895) was chosen over 695 because Chesterfield County didn't have an SR 895 but does 695.

[agentsteel53]

CA uses some numbers which are reminiscent of the former ones.  CA-11 become I-110, which happened to be the lowest available number.  but CA-7 became I-710 instead of I-310 just for easier driver recognition.

[Perfxion]

CT uses its only 3di on I-95, (395), just in case they renumber anything south of New Haven. Like US7, if that pipe dream ever is built.

[deathtopumpkins]

I'm willing to bet a fair number of these are due to canceled freeways too, like with CT I-691. 291 already exists, and 491 was planned: http://www.kurumi.com/roads/ct/i491.html

Same goes for NY/CT I-684. 284 (http://en.wikipedia.org/wiki/Interstate_284) and 484 (http://www.kurumi.com/roads/ct/i484.html) were planned, both in CT.

[TheStranger]

Another California thought:

Renumbering is something that CalTrans wants to avoid as much as possible - which isn't always a good thing, as it allows unbuilt routes to hog smaller-digit numbers, and prioritizes even the shortest existing corridors over newer (and possibly more important) routes.

Cases in point:

- The usage of future Interstate 905 for what was once state route 117 (and before that, an extension of route 75) in San Ysidro - 705 was and remains available, and 305 only exists as a FHWA paper designation and isn't in use as a signed route.

- The creation of Interstate 238 occurred while former Interstate 480 was already a short state route in SF that could have easily been renumbered to another designation.  Moving 3di designations within a metro area isn't unprecedented (it has happened in NYC in the past)

- The I-580 extension along former Route 17 specifically exists because CalTrans did not want to renumber the Central Valley state route 180 to accommodate the originally chosen designation of I-180.  (Going to the 1964 renumbering, state routes 5, 8, 15 all got nixed to accommodate interstates, and what had been state route 10 was renumbered in the late 1950s for that reason as well - yet 180 was retained then!)

- While the same thoughts behind today's I-110 and I-710 likely were in play for today's 580 and 505 (which were both originally part of the pre-1964 Interstate 5W), wouldn't assigning 105 and 180 have made sense then?  I-5 at the time had no odd 3dis, with unsigned 105 being given to the southernmost tip of US 101 briefly in 1964 (only to then be moved to today's Century Freeway in 1968)...and the only pre-1964 I-80 branch routes were the even-first-digit 280, 480, 680.

[sp_redelectric]

Washington State has just three 3dis - I-205 (whose southern end is in Oregon), I-405 around the east side of Seattle, and I-705 in Tacoma.  Why no I-105?

The argument that there's no 705 in Oregon would make sense, seeing there is I-105 in Eugene, and I-205 serves both states, but there are duplicative 405s so that Seattle's 405 should really be I-605...and Tacoma's I-705 could be I-305 or I-505.

In Oregon, I-305 was originally planned for Salem (cancelled, later became Oregon 72/Business Route 99E, Salem Parkway) and I-505 was originally planned for N.W. Portland (cancelled, stub ramp became off-ramp for U.S. 30 and Yeon Boulevard).  So that provides some logic to 705's numbering - but that logic is still defeated by the two 405s.  And Oregon/Washington don't agree with route numberings anyways - in the eastern part of the state, state route numbers always change at the state line (Oregon 3 and 11 become SR 129 and SR 125).

[roadman65]

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.

Although Florida for I-95 odd spurs are awkward, like I-195 north of I-395 and then I-595.

[Kacie Jane]

Washington State has just three 3dis - I-205 (whose southern end is in Oregon), I-405 around the east side of Seattle, and I-705 in Tacoma.  Why no I-105?

It's to not conflict with state routes.  SR 105, 305, and 505 all exist.  (Also, it serves as a continuation of SR 7 -- I think that's more of a coincidence, though, and the first thing I said is the actual reason.)

[agentsteel53]

It's to not conflict with state routes.  SR 105, 305, and 505 all exist.  (Also, it serves as a continuation of SR 7 -- I think that's more of a coincidence, though, and the first thing I said is the actual reason.)

the state routes were numbered that way in 1964, correct?  when did WA decide on its interstate numbers?

[NE2]

I-705 was legislatively created in 1979 (it wasn't an original Interstate).

[KEVIN_224]

Connecticut uses the following:

I-384 from I-84 Exit 59 in East Hartford to US Routes 6 and 44 in Bolton.
I-684 in Greenwich, mostly between exits 2 and 3 in Westchester County, NY.
I-291 from I-91 Exit 35A in Windsor to I-84 Exit 61 in Manchester.
I-691 from I-91 Exit 17 (NB) and 18 (SB) in Meriden to I-84 Exit 27 at the Cheshire/Southington town line.
I-395 from Exit 76A (NB) in East Lyme to the MA state line in Thompson.

[Alps]

How about I-481 in New York and I-587/I-787? Maybe it's worth trying to complete this list. I-393 NH is another.

[Kacie Jane]

187 and 387 both existed at one point, though, correct?

[Alps]

187 and 387 both existed at one point, though, correct?

"On Aug. 22, 1958, the New York Department of Public Works submitted "Interstate 387" for the New York State Thruway between Elmsford and Suffern. On Aug. 29, 1958, AASHO replied that this should be called I-287 and connect to a proposed I-287 in New Jersey."

I know nothing of I-187.

[Kacie Jane]

I've looked this up dozens of times, yet can never remember the answer when it inevitably comes up again.  187 and 387 were both proposed numbers for I-287 in New York (187 east of I-87 in Elmsford, 387 west of there -- 87 at the time still planned to stay east of the Hudson).  However, AASHO said no, and when the highway was finished, it was signed as 287 west of Elmsford, and 487 east of Elmsford, with 287 quickly usurping the whole route.

So according to Kurumi's site, I-187 and I-387 existed, but only on paper, and for only about a week.

[Kacie Jane]

"On Aug. 22, 1958, the New York Department of Public Works submitted "Interstate 387" for the New York State Thruway between Elmsford and Suffern. On Aug. 29, 1958, AASHO replied that this should be called I-287 and connect to a proposed I-287 in New Jersey."

I know nothing of I-187.

I'm curious where you got that quote from, Steve, as wherever it was should have had a nearly identical quote regarding 187.

[NE2]

http://www.kurumi.com/roads/3di/ix87.html
187, 387, and 587 (and probably 787) were all proposed in 1958. 187 and 387 became 487 and 287, but 587 remained.

[Kacie Jane]

If I-587 was proposed at the same time, that explains perfectly why they still skipped over 187 and 387 even though they were never signed.  No sense changing the number if AASHO doesn't make them.

[Mapmikey]

Virginia seems to just not want to disrupt its numbering system anymore. The last Virginia state route renumbered for a 3di was VA 195 (now 186) in the 1970s. Since then I-564 was created with VA 164 and 364 already extant. I-785 will just be an extension of NC's, and the proposed I-895 (now VA 895) was chosen over 695 because Chesterfield County didn't have an SR 895 but does 695.

I-364 was on the board early on but became I-464.  Additionally, I-564 was on the drawing board with that number before VA 364 was created in 1968.

Mapmikey

[Duke87]

With regards to the x81s, there is continuity across states and they increase from south to north. Virginia uses 381 and 581, skipping 181 because it already existed in Tennessee (until I-26 ate it). Likewise, New York is numbering its new spur 781 so as to continue the trend and not reuse any of the other numbers.

As for 481, Interstate Guide hypothesizes that 281 wasn't used because NY 281 was already nearby. Seems reasonable.


I-284 and I-484 were both planned in Hartford but never built, leaving 684 as an oddity. I-384 was numbered such no doubt because CT 184 already exists and Connecticut does not allow duplicate numbers. Ditto for I-395 - CT 195 already exists. Actually, CT 184 and CT 195 themselves were CT 84 and CT 95 before the interstate system invaded and took their numbers.

[Alps]

"On Aug. 22, 1958, the New York Department of Public Works submitted "Interstate 387" for the New York State Thruway between Elmsford and Suffern. On Aug. 29, 1958, AASHO replied that this should be called I-287 and connect to a proposed I-287 in New Jersey."

I know nothing of I-187.

I'm curious where you got that quote from, Steve, as wherever it was should have had a nearly identical quote regarding 187.

I'm curious why I didn't scroll up past 287 to see the 187 on top.