3 Digit Interstates

[AZDude]

I know the general rule of the first digit.  Even goes around or through city and returns to its parent route.  Odd spurs into a city never returning to its parent.  Is there a standard which determines what the first digit will be?

Example,

Lets say we want an interstate to branch off I-40 and spur into a city and not return to I-40.  Naturally the number will be either 140, 340, 540, 740, or 940.  How is the first digit chosen? 

[Voyager]

I think it's fairly random.

[AZDude]

That's what I was thinking.  Although I've noticed that 2, and 5, are used a lot.

[Alex]

In the early days of the Interstate system, the numbers were chosen from 1xx or 2xx upwards. But as the planners grew to understand how they wanted to use odds and even numbers, they had to make changes. In New York for instance, the reason why there is a I-587 and I-787 and no I-387 or I-187, is because they used I-187 and I-387 for NYC area routes before renumbering them into even routes. They didn't renumber the others for whatever reason, so you have the I-5xx and 7xx.

Stephen Summers did quite a bit of research on this in the early 2000s for his former homestead website. Included were scans of the original planning maps that were used to come up with the original 3dis for many states. That is where I saw the x87 situation and also the x90's for NY too.

[Scott5114]

Depends on what's available. There's a 240 in Oklahoma already, so if ODOT wanted to establish a new x40 Interstate, they couldn't use 240 again. Similarly if they wanted to do a spur off of I-40 around Sallisaw and call it I-540, they'd probably get shot down by AASHTO because of the possibility of confusion with I-540 in Arkansas. Other than that, AASHTO would probably accept whatever the DOT submitted in their application for an interstate route number. Texas got an I-820 even though there are no other x20s in the state.

[ssummers72]

Generaly when the state applies for a 3di designation they first have to get the route itself. i.e. point a to point b approved by the FHWA using the number the state would like to use. Then, after the route addition has been approved, AASHTO would either approve it or advise a new number to use. Usually from all the instances i've seen AASHTO approves the state requested number.

So, lets use an example:

On the 11-10-1958 AASHO approved the Phoenix spur of I-510 into Phoenix starting at I-10 & 7th Street North via 7th Street ending at Van Buren Street.

Then, on the 6-24-1969 Arizona extended I-510 Northward and Westward to the present intersection of I-10/I-17 on the West side of Phoenix and change its designation to I-410. AASHO approved this change.

Then, the BPR requested that I-410 should be changed to I-10 and extend I-17 South and East to the relocated I-10 on the South side of Phoenix. AASHO, BPR and AZ concured on the 11-17-1969.

This is kind of a rudementary example of what I think you are looking for.

Take Care,

Stephen Summers

[74/171FAN]

Even though VA 895 is not an interstate(it definitely should be) they chose 895 over 695 as there was already an SR 695 even though neither Chesterfield nor Henrico Counties(which doesn't have SRs) use 895.  I'm assuming that could be part of the reason for future I-785 in the Danville area.

[Revive 755]

I thin it is mostly random or there are state highways with the same number already present.  Arkansas seems to have an AR 340, AR 355, so that could partially explain why they went/are going with I-540 and I-555 over I-340 and I-355.  But there's no AR 330, so I don't see why it's I-530 instead of I-330.  I it is this general reason why Topeka has I-470 over I-270 since US 270 barely enters the state (are there any other places where a state could have a 3-digit interstate with the same number as  a 3-digit US Route?).

I've been told that some states don't like to use I-1xx since "1" is sometimes confused with "I-".

[WillWeaverRVA]

Even though VA 895 is not an interstate(it definitely should be) they chose 895 over 695 as there was already an SR 695 even though neither Chesterfield nor Henrico Counties(which doesn't have SRs) use 895.  I'm assuming that could be part of the reason for future I-785 in the Danville area.

Well, there's I-664 in Suffolk, though Suffolk doesn't have a SR 664 (662 and 666, but no 664).

VA 785 (future I-785, which is on US 29 in Danville) enters Pittsylvania County, which has a SR 785. If VA 785 becomes I-785, then 785 would indeed duplicate in that area.

[Greybear]

I thin it is mostly random or there are state highways with the same number already present.  Arkansas seems to have an AR 340, AR 355, so that could partially explain why they went/are going with I-540 and I-555 over I-340 and I-355.  But there's no AR 330, so I don't see why it's I-530 instead of I-330.

Revive, I must humbly beg to differ with you. There IS an AR 330, in Van Buren County, according the Arkansas State Highway and Transportation Department. There are two sections of it, actually.

Also, in the near future, there will be an I-130 in Arkansas, which will replace AR 245 on the east side of Texarkana. I-130 will be a predecessor to I-49, if and when it reaches southwest Arkansas from Louisiana.

[timhomer2009]

My guess is that numbers will increase from west to east, or north to south, much like the parent routes (the obvious exception being I-238 in California).  Note:  the rule would apply to 3-digits from the same parent route.

For example, (hidden) I-110 in El Paso is west of I-410 in San Antonio, which is west of I-610 in Houston.

[Revive 755]

My guess is that numbers will increase from west to east, or north to south, much like the parent routes (the obvious exception being I-238 in California).  Note:  the rule would apply to 3-digits from the same parent route.

For example, (hidden) I-110 in El Paso is west of I-410 in San Antonio, which is west of I-610 in Houston.

Theory works, including dead routes or numbers, but excluding future routes:
* AL:  this state may be the best example of leaving space for future spurs in this number scheme.
- I-59
- I-65

* CO (with I-425 once considered for I-270)

* IL
- I-55
- I-74, since the preliminary numbering around Quad Cites had an I-274

* IN
- I-65

* KS
- Both I-35 and I-70

* MI
- I-75
- I-96

* MO
- I-55 (assuming MO 755 was going to eventually be promoted from state route to interstate)

* MT
- I-15

* LA
- I-10

* OH
- I-80

* SC
- I-26
- I-85

* TN
- I-40 (if I-840 came that much later than I-640)

* TX
- I-10
- I-35? I-635 at Dallas allows for future routes in San Antonio and Austin

* VA
- I-81

Theory doesn't work
* IL
- I-70 (I-870 once considered for I-270 between I-255 and I-55/I-70)

* MO
- I-70 (I-670 would be I-270, I-270 would be I-670)

* NE
- I-80 (swap I-480 and I-680; given the attempts at spurs to Grand Island and Hastings, I-180 should have a higher first digit)

* OH
- I-70 (I-470 should be in Columbus, I-670 at Wheeling)
- I-71 (swap I-271 and I-471)
- I-75 (I-475 at Dayton, I-675 at Toledo

I'm probably missing a few on both sides, plus the added complications of multi-state routes

[mightyace]

In the not category:
PA

- I-76 (I-176 east, I-276, Philly, I-376 Pittsburgh, I-476 Philly to Scranton, future I-576 Pittsburgh, I-676 Philly)
- I-79 (has I-279 and I-579 and nothing else)
- I-80 (seems to fit but 180 was designated after 380)

As for TN:
Well 840 is still a state route for now.  And the evens are OK (240 Memphis, 440 Nashville, 640 Knoxville), but you have I-140 near Knoxville.

[AZDude]

timhomer2009 wrote:

My guess is that numbers will increase from west to east, or north to south, much like the parent routes (the obvious exception being I-238 in California).  Note:  the rule would apply to 3-digits from the same parent route.

For example, (hidden) I-110 in El Paso is west of I-410 in San Antonio, which is west of I-610 in Houston.

I never thought of it that way (though I probably should have, doh!).  But that makes the most sense.  Yes there are exceptions but that will always happen.

Former I-510 in Phoenix which is west of once proposed I-710 in Tucson.  That rule applies here.

Thanks for the examples too Revive 755.

[ComputerGuy]

I-90 in WA has no auxiliary routes for its 300 mi in WA...

[TheStranger]

Trying to see if this applies to California..

I-80:
I-280, I-380 (east of I-280), I-480 (was east of the original I-280 proposal in SF), I-580 (though I think that got its number as a result of formerly being I-5W - not the only time a previous designation led to the current number), I-680...

I-780, I-880, and I-980 all came later and don't fit.

I-5 definitely doesn't work to this scheme:
I-105 (both the current second incarnation of the route, and the 1960s version along US 101 in downtown Los Angeles) was always hundreds of miles south of I-205.

I-10 strangely fits, with I-710 being east of I-110 (but still being an unusually large number in the sequence, that derived from the previous designation of Route 7).

[bugo]

I thin it is mostly random or there are state highways with the same number already present.  Arkansas seems to have an AR 340, AR 355, so that could partially explain why they went/are going with I-540 and I-555 over I-340 and I-355.  But there's no AR 330, so I don't see why it's I-530 instead of I-330.

Revive, I must humbly beg to differ with you. There IS an AR 330, in Van Buren County, according the Arkansas State Highway and Transportation Department. There are two sections of it, actually.

Also, in the near future, there will be an I-130 in Arkansas, which will replace AR 245 on the east side of Texarkana. I-130 will be a predecessor to I-49, if and when it reaches southwest Arkansas from Louisiana.

There's also an AR 130, which runs through east central Arkansas.  Part of what is now US 165 was once AR 130.  It was originally AR 30, which was renumbered when I-30 came along.

Speaking of AR 355, it was also renamed because of the interstate system, as it was originally AR 55.  Also, what was once AR 40 is now AR 140.

[TheHighwayMan3561]

*QUOTE* Scott5114 said: Texas got an I-820 even though there are no other x20s in the state. *END QUOTE*

I thought that was mainly due to the influence of one of the Dallas radio stations, 820 AM.

[Duke87]

In New York for instance, the reason why there is a I-587 and I-787 and no I-387 or I-187, is because they used I-187 and I-387 for NYC area routes before renumbering them into even routes.

All the 3dis in metro NYC are first digit even. Whether it makes sense for them to be or not:

278 (sort of), 478 (no), 678 (no), 878 (no), 280 (yes), 684 (arguably), 287 (yes), 295 (no), 495 (definitely no), 695 (yes), 895 (yes)

...of course, the x78's are a huge chunk of weirdness in and of themselves. Not orphaned, but abandoned.

[74/171FAN]

All the 3dis in metro NYC are first digit even. Whether it makes sense for them to be or not:

278 (sort of), 478 (no), 678 (no), 878 (no), 280 (yes), 684 (arguably), 287 (yes), 295 (no), 495 (definitely no), 695 (yes), 895 (yes)

...of course, the x78's are a huge chunk of weirdness in and of themselves. Not orphaned, but abandoned.

What wrong with I-278 and I-295 since they do end at interstates at both ends?

[froggie]

I-278 ends at US 1/US 9 on its western end, not at another Interstate.  Meanwhile, I-295 ends at NY 25/Hillside Ave, just south of Grand Central Pkwy.  Again...not at another Interstate.

So by the book, both routes should be odd 3-digit routes.  Though at the same time, they got their numbering because they were both intended to connect to other Interstates.

Another note on I-278:  neither it nor I-478 connect to I-78.

[74/171FAN]

I-278 ends at US 1/US 9 on its western end, not at another Interstate.  Meanwhile, I-295 ends at NY 25/Hillside Ave, just south of Grand Central Pkwy.  Again...not at another Interstate.

So by the book, both routes should be odd 3-digit routes.  Though at the same time, they got their numbering because they were both intended to connect to other Interstates.

Another note on I-278:  neither it nor I-478 connect to I-78

First these interchanges are close enough to other interstates that it's warranted(as the end is just afterward).  I-678 and I-878 don't connect tp I-78 either BTW.

[Michael]

3DI's of I-90 in New York increase in numbering from west to east (except I-990):

Buffalo:

• 190
• 290
• 990

Rochester:

• 390
• 490
• 590

Syracuse:

• 690

Utica:

• 790

Albany:

• 890

[74/171FAN]

I-295's south end is a mile-and-a-half and 2 full interchanges past I-495.

I got I-495 confused with the Grand Central Pkwy   The theory also works on I-85 in SC(I-185, I-385, and I-585(even though it doesn't currently begin at I-85).

[Avalanchez71]

Why is it that NC is compelled to change their 3 di numbering scheme but when GA and SC finish a loop I-520 they do not change the numbering?