3-digit Interstates that begin and end at different Interstates: odd or even?

[Henry]

I can cite some for IL...

I-155 Peoria: I-55 to I-74
I-355 Chicago: I-80 to I-290
Proposed I-490 Chicago: I-290 to I-90
I-255 St. Louis area: I-55 (in MO) to I-270

Several good examples of AASHO rejecting odd first digits for obvious bypasses:



TLDR: it looks like the original rule was to always use an even first digit if both ends were at another Interstate, except for I-105 and I-110 in Los Angeles (which ended at each other, and access from I-110 to I-105 didn't exist at first). I-335 Minneapolis (ca. 1964) was probably the first to break this rule.

Also, NC had not one, but two 3di's that were rejected: I-185 Winston-Salem (future I-285) and I-195 Fayetteville (future I-295). However, I'm genuinely surprised that I-540 was kept on the Raleigh outer beltway, despite rumors and suggestions that it should become I-640 upon completion.

[PHLBOS]

When I-195 RI/MA was originally constructed, it ended at MA 25, which went all the way to MA 24 in Raynham at the time. As such, I-195 was a true spur of I-95.

True, but in and of itself, I-195 didn't change.

MA 25 between Raynham and Wareham wasn't redesignated as part of I-495 until 1975.  The additional I-495 mileage was a trade-off for the discontinued mileage of I-95 through Boston and the I-695 Inner Belt.

FTFY.  The original wording of your post might confuse those unfamiliar with what happened.

As for I-290, it was originally proposed to continue past I-495 in Marlborough and rejoin I-90/MassPike in Framingham, until it was stopped by the rich NIMBYs in Hudson.

There was a later plan for I-290 to be extended to I-95/MA 128 as well.

[NE2]

At the time the East Los Angeles 110 & 105 existed, there was full access at the San Bernardino Split for all movements (with the flyover ramp that would eventually be removed post-Northridge).

Did the flyover exist by 1958? It was not part of the original interchange.

[TheStranger]

At the time the East Los Angeles 110 & 105 existed, there was full access at the San Bernardino Split for all movements (with the flyover ramp that would eventually be removed post-Northridge).

Did the flyover exist by 1958? It was not part of the original interchange.

Via historicaerials: by 1964, it did, but it wasn't there in 1952. It appears on a 1956 topographic map as well.

[GaryV]

Michigan is inconsistent, with one odd first digit and three even first digits. I-196 connects I-96 in Grand Rapids with I-94 near Benton Harbor. I-275 connects with I-75 with I-96 in the Detroit area. I-296 (unposted) connects I-96 with I-196 in Grand Rapids. I-696 connects I-96 with I-94 in the Detroit area.

Of course I-275 was supposed to connect back up with I-75 to the north, but the residents got it blocked.

And I-196 was originally the road from GR to Muskegon; it got switched.

[bzakharin]

I-287 in NJ/NY starts and ends at I-95 with a long segment multiplexing with its parent, I-87, in the middle. It is often used to bypass I-95 through NYC (Although in NJ, the shorter bypass is the Garden State Parkway to 287 in NY). I always thought it should have been x95, but all even x95s are taken in New York.

[triplemultiplex]

For my own fictional musings, I generally want even 3di's for anything that connects two interstates.  Unless it would mean exhausting the state's "supply" of even 3di's for that mainline interstate.  But there are always going to be exceptions.

Out in the real world, the mishmash of 'rules' for these 3di's seem to reflect varying degrees of someone at AASH(T)O caring.  The present time is an era where they do care; for new 3di's at least.  NC's experience as evidence.

[ET21]

Only one for Chicagoland proper atm

I-355: I-290 north end, I-80 south end

[kkt]

For my own fictional musings, I generally want even 3di's for anything that connects two interstates.  Unless it would mean exhausting the state's "supply" of even 3di's for that mainline interstate.  But there are always going to be exceptions.

Out in the real world, the mishmash of 'rules' for these 3di's seem to reflect varying degrees of someone at AASH(T)O caring.  The present time is an era where they do care; for new 3di's at least.  NC's experience as evidence.

It's interesting.  Most people seem to agree with the principle that even 3di's should be used to connect two interstates.  But for most of the major interstate construction period it was policy that all interstates end at other interstates, or national borders or major geographic obstacles.  So most 3dis did end at other interstates because they had to.  Then, there are fewer even 1st digits available (2, 4, 6, 8) than odd 1st digits (1, 3, 5, 7, 9).  So those policies produce a shortage of even 1st digit 3di numbers and quite a few states run out and use anything they can.

If I were writing policy for 3dis, I would either attach no significance to the 1st digit or use evens only for beltways and bypasses and odds for everything else.