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

[The High Plains Traveler]

First digit, that is.

There is a lot of inconsistency in how 3dIs that begin and end at different Interstate routes are numbered. Some have odd first digits, others have even. This is true even within the same state.  In California, there is I-505 between I-5 and I-80, and I-580 that used to run between I-5 and I-80 before it was extended, but I-205 runs between I-5 and I-580. Is there a rule that governs this, where the 3dI is neither a true loop nor a spur?

[NE2]

No, there is no rule.

Note wrt your example that 505 and 580 were originally 5W.

[hbelkins]

Kentucky has three 3dis that are not true loops. All of them start with even numbers and all end at different routes.

264: 64, 71.
265: 65, 71 (and even when it's extended into Indiana, it will end at two different routes.
471: 275, 71.

[PHLBOS]

Is there a rule that governs this, where the 3dI is neither a true loop nor a spur?

FWIW, according to a short write-up listed on many Rand McNally Maps & Atlases; even 3dis typically either loop around or go through a city whereas odd 3dis, generally, spur into a city. 

However, some liberties were taken along the way when numbering 3dis; in some instances, even prior to some states running out of applicable 3di numbers.

Anyway, here's a short-list of 3dis that end at different Interstates that I know of off-hand:

I-476 in PA (from I-95 to I-81)
I-283 in PA (from I-76 to I-83)
I-279 in PA (from I-376 to I-79)
I-376 in PA (from I-80 to I-76)
I-380 in PA (from I-80 to I-81)

I-195 in RI/MA (from I-95 to I-495)
I-290 in MA (from I-90/395 to I-495)
I-291 in MA (from I-91 to I-90)
I-395 in CT/MA (from I-95 to I-90/290)

I-695 in NY (from I-295 to I-95)
I-895 in NY (from I-278 to I-95)

I-695 in DC/VA (from I-395 to I-295)

[ekt8750]

Is there a rule that governs this, where the 3dI is neither a true loop nor a spur?

According to a short write-up listed on many Rand McNally Maps & Atlases; even 3dis typically either loop around or go through a city whereas odd 3dis, generally, spur into a city. 

However, some liberties were taken along the way when numbering 3dis; in some instances, even prior to some states running out of applicable 3di numbers.

Anyway, here's a short-list of 3dis that end at different Interstates that I know of off-hand:

I-476 in PA (from I-95 to I-81)
I-283 in PA (from I-76 to I-83)
I-279 in PA (from I-376 to I-79)
I-376 in PA (from I-80 to I-76)
I-380 in PA (from I-80 to I-81)

I-195 in RI/MA (from I-95 to I-495)
I-290 in MA (from I-90/395 to I-495)
I-291 in MA (from I-91 to I-90)
I-395 in CT/MA (from I-95 to I-90/290)

I-695 in NY (from I-295 to I-95)
I-895 in NY (from I-278 to I-95)

I-695 in DC/VA (from I-395 to I-295)

I-476 is one of the poster children of weird 3dis. It intersects I-76 almost right at its mid point. Shouldn't 3dis at least be branches or spurs off their parents?

[PHLBOS]

I-476 is one of the poster children of weird 3dis. It intersects I-76 almost right at its mid point. Shouldn't 3dis at least be branches or spurs off their parents?

As previously stated, Interstate spurs are normally odd 3dis (which I-476 is not).  Even 3dis don't have to begin/end off their 2di parent; especially if the route's a loop or beltway.

Keep in mind that prior to the mid-90s; the NE Extension of the PA Turnpike wasn't part of I-476, which ended at the I-276/Mid-County interchange (roughly 3 to 4 miles north of its interchange w/I-76).

Another two to add:

I-291 in CT (from I-91 to I-84)
I-691 in CT (from I-84 to I-91)

[Pink Jazz]

I-264 in Hampton Roads, Virginia contains both a loop and a spur (the latter added as part of the renumbering of SR 44 in 1999).  Also, I-464 goes from I-64 to I-264 (I actually heard somewhere that it was originally supposed to be numbered I-364).

[TheStranger]

California (beyond the 505/580 examples mentioned earlier) -

280: begins at 680 and original north terminus was planned to have been 480, and later planned to have been 80
480: original west terminus was at planned 280, while east terminus was 80
680: south terminus is at 280, north terminus is at 80
780: east terminus is at 680, west terminus is at 80
880: south terminus is at 280, north terminus is at 80/580
980: west terminus is at 880 (note: originally state route 17 prior to 1984), east terminus is at 580

205: west terminus is at 580, east terminus is at 5
405: both ends are at 5
605: south end is at 405, north end is at 210
805: both ends are at 5

210: west end is at 5, (future) east end is at 10

215: both ends are at 15

[adventurernumber1]

Interstate 520 in the Augusta, GA area has an odd number at the beginning and is a loop, but that's actually because it used to be a spur that didn't connect back. It used to run from I-20, around Augusta to right before the SC border. It has been extended into SC to connect to I-20 on the other side of Augusta.

Maybe some of these 3-digit interstates that break the rules have been extended, and used to not break the rules. That's the case for I-520.

[mhh]

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.

[robbones]

Little Rock, AR metro
430: 40, 30
630: 430, 30
440: 30/530, 40

In the future:
530: 30/440, 69

[KG909]

As TheStranger mentioned, I-210 in California has it's west end at I-5, but it's east end is at CA 57 and CA 210. If CA 210 is ever renumbered I-210, it's east end will be I-10.

[WNYroadgeek]

Four more for New York:

I-290 (I-90 to I-190)
I-390 (I-86 to I-490)
I-590 (I-390 to I-490)
I-690 (I-90 to I-481)

[cjk374]

I-220 in Mississippi:  west side of Jackson (Clinton) on I-20, runs north to I-55.

[jp the roadgeek]

I-495 in MA (I-195 and I-95),
I-495 (unsigned) in ME (I-95 and I-295)
I-276 in PA (I-95 and I-76)
I-676 in NJ/PA (I-76 and I-295)
I-684 (I-84 and I-287)

[ekt8750]

I-495 in MA (I-195 and I-95),
I-495 (unsigned) in ME (I-95 and I-295)
I-276 in PA (I-95 and I-76)
I-676 in NJ/PA (I-76 and I-295)
I-684 (I-84 and I-287)

I-676 starts and ends at I-76. Just in 2 different states. It ends with that interchange with I-76 and NJ-76C (is that really that road's designation?) at the foot of the Walt Whitman Bridge.

[NE2]

List of early routes that weren't obvious bypasses/loops or spurs:
*I-105 and I-110 Los Angeles: ended at each other, but clearly spurs
*I-505 and I-580 Frisco: renumbered from I-5W in about 1964
*I-605 and I-210 Los Angeles: logical bypasses
*I-225 Denver: obviously a bypass, but provides a good illustration of an even number that doesn't return
*I-335 Minneapolis: added about 1964, perhaps the first odd number for a bypass connection of this type
*I-255 Memphis: now I-240 from the I-55 'bump' north to I-40 downtown; seems more like a spur than a bypass
*I-264 and I-464 Norfolk: early case of the mainline bypassing with 3DIs into downtown (AASHO explicitly replaced 364 with 464)
*I-471 Cinci: I suppose it could be called a bypass of I-71
*I-478 NYC (Manhattan Bridge): another spur of sorts that connected two Interstates
*I-280 NJ: another such spur
*I-480 Omaha: ditto

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.

[froggie]

*I-335 Minneapolis: added about 1964, perhaps the first odd number for a bypass connection of this type

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.

The original design for I-335 did not have it connecting to I-94, which would explain the odd number designation.

Regarding the OP, I've always interpreted FHWA guidance on 3di numbering to where an auxiliary interstate that "connects Interstate routes" can have an even prefix (so I-476 PA or I-271 OH would be valid).  Though we have so much variability because of different state (and AASHTO or regional BPR office) interpretations, as well as cases where a state simply ran out of prefix's (namely CA and NY).

[PHLBOS]

I-684 (I-84 and I-287)

Though it's not fully signed as such, I-684 actually runs north of I-84 and ends at US 6/202/NY 22. 
Note the END 684 sign in the distance.

[roadman]

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.

MA 25 between Raynham and Wareham wasn't redesignated as part of I-495 until 1975.  It was part of the discontunance of I-95 through Boston and the I-695 Inner Belt.

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.

[freebrickproductions]

In Alabama, the proposed I-222 would run from I-22 to the proposed I-422.
There's also the proposed I-685 which would run between I-65 and I-85 in Montgomery as well.

[J N Winkler]

A question re. the map extracts--what's the source, and who made the corrections in ballpoint?

[NE2]

A question re. the map extracts--what's the source, and who made the corrections in ballpoint?

The source is Stephen Summers's short-lived (and not completely archived) site, linked from Kurumi's entries. Apparently AASHO made the changes.

[NE2]

The original design for I-335 did not have it connecting to I-94, which would explain the odd number designation.

That makes sense. So unless there was one before 1967, the first may have been the 96/196 swap (1969), which put I-196's end at I-94. Then 1971 brought I-376 (was part of I-76; no even numbers were available besides 876, which was renumbered 479 simultaneously), I-380 (was I-81E) came in 1972, I-135 (was I-35W) in 1976, and I-170 Missouri (1978) was the first new odd route with both ends at another Interstate.

[TheStranger]

List of early routes that weren't obvious bypasses/loops or spurs:
*I-105 and I-110 Los Angeles: ended at each other, but clearly spurs

I wonder if the assumed "terminus" that justified the odd first digit was US 101 at the San Bernardino Split - which interestingly is counter to the then-planned setup for the 280/480/101 (and current 280/680/101) junction.

*I-255 Memphis: now I-240 from the I-55 'bump' north to I-40 downtown; seems more like a spur than a bypass

Tying into the other thread about 55's original planned Memphis routing, could the old 255 (now 240/future 69) + the current newer bridge (40) be seen as a loop alternate to 55?

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).

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).

As TheStranger mentioned, I-210 in California has it's west end at I-5, but it's east end is at CA 57 and CA 210. If CA 210 is ever renumbered I-210, it's east end will be I-10.

Prior to 1998, that east end was at the current 10/57/71 junction (the originally built eastern terminus of 210), so the interstate did connect to 10 for most of its existence.