How did the children get their names ^H^H^H^H^H^H numbers?

[hbelkins]

Curious as to how the 3dis were numbered when the 3di ended up as a child of a route other than the lowest-numbered interstate in a city?

Why, for instance, is the Atlanta bypass 285 instead of an x20?

Or why isn't I-675 in Dayton an x70 instead?

[hotdogPi]

There is no rule that it has to be the lowest number.


For some (I-291 MA is an example), the lower number already exists.

[Zeffy]

Okay, I have to ask.

What the hell is ^H^H^H^H^H^H supposed to mean? 

[sammi]

Okay, I have to ask.

What the hell is ^H^H^H^H^H^H supposed to mean? 

Backspace. So the title actually says

How did the children get their  numbers?

(with two spaces between the last two words )

[Stratuscaster]

To those of us old enough, ^H is a backspace.

[Molandfreak]

To bring this back on topic (ahem...), In the case of I-285, GA probably thought it was best to have a completely different number for both planned bypass-function Interstates, to minimize confusion (I-285, I-420). I actually wish that kind of logic existed nationwide...

[english si]

Texas seems to go for the longest interstate as parent of full loops - so 410, 610, 820 (Dallas' not-full loop is a bit strange as 635 was used for it) other states seem similar when it comes to full loops.

SC I-385 is strange, as it is surely more a spur of I-26.
NC I-840 ought to be an I-x85, rather than take the last I-x40

[hbelkins]

I opted for the (backspace) because strikethru text is not available for thread titles.

[1995hoo]

Hmmm. Gave my the interesting mental image of the Capital Beltway's eastern side having an I-466/I-95 concurrency (this because I-266 was already planned for a route in Arlington).

[Thing 342]

Not sure about parents, but it seems like the first number is based off of their relative length during planning. 2 goes to the longest loop, 4 to the next longest, etc.

[bulldog1979]

Not sure about parents, but it seems like the first number is based off of their relative length during planning. 2 goes to the longest loop, 4 to the next longest, etc.

In Michigan, they're numbered west-to-east or south-to-north. The first bypass for I-96 on the west end is I-296 in Grand Rapids, next is I-496 in Lansing and lastly I-696 by Detroit. Going north along I-75, we have I-275 in the Detroit area, I-475 at Flint and I-675 at Saginaw.

[Duke87]

For Connecticut, I-384 and I-395 got those numbers because CT 184 and CT 195 already existed and ConnDOT won't allow number duplication. Consider that those two state highways were formerly CT 84 and CT 95 before the arrival of the mainline interstates forced their renumbering and you can't blame ConnDOT for not wanting to renumber them a second time.

I-291 is the lowest even digit possible for x91, but why not make it an x84? Well, separate highways numbered I-284 and I-484 were also planned in the Hartford area, but never built, so 291 fit in a more comprehensive system that never came to be. 

Likewise, I-491 was planned (also in the Hartford area!) but never built, and I-684 already existed in Connecticut because of how New York built it... so I-691 got its number because it was, considering the other then still-active proposals, the lowest even x84 or x91 available for that road.

[kurumi]

A couple clarifications on Connecticut:
* CT 195 was never CT 95 (though today's CT 184 was numbered 95 for a short time)
* I-291 numbering (c. 1957) predates I-284 and I-484 (introduced 1976)

[woodpusher]

Not sure about parents, but it seems like the first number is based off of their relative length during planning. 2 goes to the longest loop, 4 to the next longest, etc.

I thought I had noticed a West to East trend for the even numbers.
TN:  Memphis 240, Nashville 440, Knoxville 640
NC:  Asheville 240, Raleigh 440
I'll check it out more thoroughly when I get a chance.

Loops seem a bit more common than spurs....
PA has Williamsport 180 Scranton 380
GA Columbus 185 Atlanta 985

[bzakharin]

How about I-287? Shouldn't it be x95 since it starts and ends at that route?

[TEG24601]

Actually, that forces me to ask the question that has bothered me for more than a decade of cross-country travel...


Why don't they Twin cities have a single route number for their Beltway?  It bothers me to no end that it is I-494 and I-694, when nearly everyone else uses 1 number for a beltway.


Why did Oregon choose I-405 for their downtown route, instead of 605 or 805, so it would be less likely to be confused with Seattle's I-405?

[hbelkins]

I thought I had noticed a West to East trend for the even numbers.
TN:  Memphis 240, Nashville 440, Knoxville 640

Thanks for mentioning Nashville. Why wasn't I-440 named I-224 instead?

Actually, that forces me to ask the question that has bothered me for more than a decade of cross-country travel...


Why don't they Twin cities have a single route number for their Beltway?  It bothers me to no end that it is I-494 and I-694, when nearly everyone else uses 1 number for a beltway.

And there is the curious case of I-255 and I-270 in St. Louis. I-270 could have been the full loop and that segment of I-270 between I-255 and I-55/I-70 could have been a different route number. Of course the lowest numbered interstate in STL is I-44.

[vtk]

Not sure about parents, but it seems like the first number is based off of their relative length during planning. 2 goes to the longest loop, 4 to the next longest, etc.

That's the way I think it should be.  That's the way it is in Ohio (roughly), but I think that was by accident.  It's plausible they tried to follow the Michigan model described above, but it got messed up when some new 3dIs were added.

[akotchi]

Actually, that forces me to ask the question that has bothered me for more than a decade of cross-country travel...


Why don't they Twin cities have a single route number for their Beltway?  It bothers me to no end that it is I-494 and I-694, when nearly everyone else uses 1 number for a beltway.

And there is the curious case of I-255 and I-270 in St. Louis. I-270 could have been the full loop and that segment of I-270 between I-255 and I-55/I-70 could have been a different route number. Of course the lowest numbered interstate in STL is I-44.

Perhaps there is an unwritten rule that the parent of the beltway number needed to be a through interstate.  Such examples include Baltimore (I-70[N] and I-83 end there, so the beltway is an I-x95), Washington (I-66 and I-270, I-70S at one time, end there, so the beltway is an I-x95), and Jacksonville, FL (I-10 ends there, and the beltway is an I-x95).  Not sure how consistently that is used across the country.

[Quillz]

Then there are examples like I-205 in California. It technically could have been an x80 3di, but it makes perfect sense to be the 205 since it takes you "to I-5"

I feel the same about 580. It could have reasonably been numbered 380, 780 or 980, but it connects both the 5 and the 80.

[JCinSummerfield]

In Michigan, they're numbered west-to-east or south-to-north. The first bypass for I-96 on the west end is I-296 in Grand Rapids, next is I-496 in Lansing and lastly I-696 by Detroit. Going north along I-75, we have I-275 in the Detroit area, I-475 at Flint and I-675 at Saginaw.

So what happened to I-175? 

[TEG24601]

In Michigan, they're numbered west-to-east or south-to-north. The first bypass for I-96 on the west end is I-296 in Grand Rapids, next is I-496 in Lansing and lastly I-696 by Detroit. Going north along I-75, we have I-275 in the Detroit area, I-475 at Flint and I-675 at Saginaw.

So what happened to I-175? 

Well, this rule is true for the loops/bypasses.  175 would have been a spur, but if it had been planned it was cancelled.  Regarless, MDOT wanted to stay consistent, I-375 was so named because it was after I-275.

[getemngo]

In Michigan, they're numbered west-to-east or south-to-north. The first bypass for I-96 on the west end is I-296 in Grand Rapids, next is I-496 in Lansing and lastly I-696 by Detroit. Going north along I-75, we have I-275 in the Detroit area, I-475 at Flint and I-675 at Saginaw.

So what happened to I-175? 

Well, this rule is true for the loops/bypasses.  175 would have been a spur, but if it had been planned it was cancelled.  Regarless, MDOT wanted to stay consistent, I-375 was so named because it was after I-275.

That doesn't explain why I-196 is after I-296, though - and that would have still been true before I-96 and I-196 were switched west of Grand Rapids. If there were ever a proposed I-175, that's news to me (and I'd love to hear about it!).

Since non-roadgeeks in Grand Rapids still confuse "I-96" and "196" to this day, and I-375 wasn't planned and was commissioned after I-196 and I-194, perhaps MDOT decided no more 3di's should start with a 1 to prevent "motorist confusion." Motorist confusion is how MDOT successfully petitioned AASHTO to let them stop signing I-296, and it's also an alleged reason why M-6 didn't get an I-x96 designation.

[Pete from Boston]

It always baffled me that 287 was not an x95, but I guess with the complete mess of Interstate secondary routes in New York, there just weren't enough to go around.

[Zeffy]

It always baffled me that 287 was not an x95, but I guess with the complete mess of Interstate secondary routes in New York, there just weren't enough to go around.

It's interesting how I-287 multiplexes with I-87, it's parent route before dying at I-95 in Port Chester, NY, or becoming NJ 440 near Perth Amboy in NJ. They could've used I-995 (looks awkward doesn't it?) if nothing else would've worked. Yet I still don't think I-287 should be renumbered.