How are the parent route for 3dus decided?

[SkyPesos]

I was looking at 3dus routes today, and noticed that a lot of them are child routes of shorter 2dus even if a longer one without that many child routes also intersect or concurrent with it. Like US 6's (2nd longest 2dus) highest first digit 3dus is 206, and US 40's (another transcon route) is 340. The two long, almost perpendicular diagonals, US 52 and US 62, don't have any 3dus (US 152 used to exist). I mentioned in fictional before that US 68 could become 162 and 412 could be 68, but that's a different topic. Then, there are shorter 2dus with tons of 3dus, like US 22 goes up to 522 and US 21 goes up to 521.

Speaking of the x21s, the new US 121 doesn't even intersect the current routing of US 21, and does intersect US 23, so why wasn't US 323 used instead? Same with US 521, probably could've been US 115, and US 15 doesn't have any 3dus children. And US 421's routing looks to fit more as a child of US 25 (another 2dus without any 3dus routes) than as US 21's.

Though some of those 3dus could be turned into a 2dus. White-out the last 2 in US 322, and you get US 32!

[Flint1979]

They go in order starting with 1 and going up. So like US-127 is the first spur of US-27 and then the second one would be US-227 and so on.

[Scott5114]

They go in order starting with 1 and going up. So like US-127 is the first spur of US-27 and then the second one would be US-227 and so on.

No, the question wasn't "why is US-127 not US-227", it's "why is US-127 not US-125" (or any other N-S 2di it intersects).

The 3dus numbering rules are quite a bit more loosey-goosey than 3di numbering rules, probably because they have to maintain at least a token attempt at direction parity while 3dis don't (you can have an east-west 3di with a north-south parent route). I'm pretty sure what they did on most of them was just try to identify which of the intersecting 2duses the 3dus most closely shadows in terms of corridor, and then went with that. But it's been almost 100 years since the system was established, and exceptions abound, especially since so many routes have been extended and cut back several times throughout their history.

[Max Rockatansky]

They go in order starting with 1 and going up. So like US-127 is the first spur of US-27 and then the second one would be US-227 and so on.

No, the question wasn't "why is US-127 not US-227", it's "why is US-127 not US-125" (or any other N-S 2di it intersects).

The 3dus numbering rules are quite a bit more loosey-goosey than 3di numbering rules, probably because they have to maintain at least a token attempt at direction parity while 3dis don't (you can have an east-west 3di with a north-south parent route). I'm pretty sure what they did on most of them was just try to identify which of the intersecting 2duses the 3dus most closely shadows in terms of corridor, and then went with that. But it's been almost 100 years since the system was established, and exceptions abound, especially since so many routes have been extended and cut back several times throughout their history.

Some like US 666 didn't even follow the cardinal direction of their parent highway.  That would be a prime example of the parent Route was simply just a notable 2D US Route somewhere in the middle of the alignment

[Roadgeekteen]

It's whatever the people in charge felt like. No real rhyme or reason.

[Scott5114]

They go in order starting with 1 and going up. So like US-127 is the first spur of US-27 and then the second one would be US-227 and so on.

No, the question wasn't "why is US-127 not US-227", it's "why is US-127 not US-125" (or any other N-S 2di it intersects).

The 3dus numbering rules are quite a bit more loosey-goosey than 3di numbering rules, probably because they have to maintain at least a token attempt at direction parity while 3dis don't (you can have an east-west 3di with a north-south parent route). I'm pretty sure what they did on most of them was just try to identify which of the intersecting 2duses the 3dus most closely shadows in terms of corridor, and then went with that. But it's been almost 100 years since the system was established, and exceptions abound, especially since so many routes have been extended and cut back several times throughout their history.

Some like US 666 didn't even follow the cardinal direction of their parent highway.  That would be a prime example of the parent Route was simply just a notable 2D US Route somewhere in the middle of the alignment

Ah, I stand corrected. In my state all of the 2duses follow the direction of their parents, so I forgot that there were examples of that not being true like US-666 (which actually follows the parity rule now that it's 491).

[US 89]

They go in order starting with 1 and going up. So like US-127 is the first spur of US-27 and then the second one would be US-227 and so on.

No, the question wasn't "why is US-127 not US-227", it's "why is US-127 not US-125" (or any other N-S 2di it intersects).

The 3dus numbering rules are quite a bit more loosey-goosey than 3di numbering rules, probably because they have to maintain at least a token attempt at direction parity while 3dis don't (you can have an east-west 3di with a north-south parent route). I'm pretty sure what they did on most of them was just try to identify which of the intersecting 2duses the 3dus most closely shadows in terms of corridor, and then went with that. But it's been almost 100 years since the system was established, and exceptions abound, especially since so many routes have been extended and cut back several times throughout their history.

Some like US 666 didn’t even follow the cardinal direction of their parent highway.  That would be a prime example of the parent Route was simply just a notable 2D US Route somewhere in the middle of the alignment

Ah, I stand corrected. In my state all of the 2duses follow the direction of their parents, so I forgot that there were examples of that not being true like US-666 (which actually follows the parity rule now that it's 491).

US 550 is another example, although for much of its history it never even intersected any odd 2dus route anyway. I suppose the same is true of 666.

[SkyPesos]

Some like US 666 didn't even follow the cardinal direction of their parent highway.  That would be a prime example of the parent Route was simply just a notable 2D US Route somewhere in the middle of the alignment

Ah, I stand corrected. In my state all of the 2duses follow the direction of their parents, so I forgot that there were examples of that not being true like US-666 (which actually follows the parity rule now that it's 491).

US 550 is another example, although for much of its history it never even intersected any odd 2dus route anyway. I suppose the same is true of 666.

US 220 is another one. In a perfect numbering system, it would make a good US 17.

[hbelkins]

I was looking at 3dus routes today, and noticed that a lot of them are child routes of shorter 2dus even if a longer one without that many child routes also intersect or concurrent with it. Like US 6's (2nd longest 2dus) highest first digit 3dus is 206, and US 40's (another transcon route) is 340. The two long, almost perpendicular diagonals, US 52 and US 62, don't have any 3dus (US 152 used to exist). I mentioned in fictional before that US 68 could become 162 and 412 could be 68, but that's a different topic. Then, there are shorter 2dus with tons of 3dus, like US 22 goes up to 522 and US 21 goes up to 521.

Speaking of the x21s, the new US 121 doesn't even intersect the current routing of US 21, and does intersect US 23, so why wasn't US 323 used instead? Same with US 521, probably could've been US 115, and US 15 doesn't have any 3dus children. And US 421's routing looks to fit more as a child of US 25 (another 2dus without any 3dus routes) than as US 21's.

Though some of those 3dus could be turned into a 2dus. White-out the last 2 in US 322, and you get US 32!

A number of these relate to extensions and decommissioning over the years. To cite your examples, there have been past incarnations of US 106, US 140, and US 240, that have been decommissioned. And US 206 only reached its parent due to a short concurrency with US 209, whereby US 206 ended but US 209 continued concurrent with US 6.

US 21 used to extend all the way north to Cleveland, but was decommissioned in stages as I-77 was completed. It was mostly concurrent with other routes (US 52, US 19, US 60) from Wytheville to Charleston. So while US 121 comes close to intersecting its former parent (the designation will probably end at the WV Turnpike, short of meeting what was US 21 in Beckley) a more appropriate number would be an X23 or even an x60, since it will intersect US 460.

As for US 421, it has undergone several extensions over the years. On Facebook the other day, someone (believe it was Chris Curley) posted a newspaper story mentioning the extension of US 421 from Bristol through SW Virginia and into Kentucky. The extension across the river and into Indiana came later.

They go in order starting with 1 and going up. So like US-127 is the first spur of US-27 and then the second one would be US-227 and so on.

No, the question wasn't "why is US-127 not US-227", it's "why is US-127 not US-125" (or any other N-S 2di it intersects).

The 3dus numbering rules are quite a bit more loosey-goosey than 3di numbering rules, probably because they have to maintain at least a token attempt at direction parity while 3dis don't (you can have an east-west 3di with a north-south parent route). I'm pretty sure what they did on most of them was just try to identify which of the intersecting 2duses the 3dus most closely shadows in terms of corridor, and then went with that. But it's been almost 100 years since the system was established, and exceptions abound, especially since so many routes have been extended and cut back several times throughout their history.

This is another case where an extension came into play. US 127 originally ran only through Michigan, Indiana, and Ohio. It wasn't extended south into Kentucky and Tennessee until the mid-1950s. It may not have even intersected US 25 in Cincinnati on its old route, although a check of Dale Sanderson's US Ends page would probably be required to make that determination.

[SkyPesos]

I was looking at 3dus routes today, and noticed that a lot of them are child routes of shorter 2dus even if a longer one without that many child routes also intersect or concurrent with it. Like US 6's (2nd longest 2dus) highest first digit 3dus is 206, and US 40's (another transcon route) is 340. The two long, almost perpendicular diagonals, US 52 and US 62, don't have any 3dus (US 152 used to exist). I mentioned in fictional before that US 68 could become 162 and 412 could be 68, but that's a different topic. Then, there are shorter 2dus with tons of 3dus, like US 22 goes up to 522 and US 21 goes up to 521.

Speaking of the x21s, the new US 121 doesn't even intersect the current routing of US 21, and does intersect US 23, so why wasn't US 323 used instead? Same with US 521, probably could've been US 115, and US 15 doesn't have any 3dus children. And US 421's routing looks to fit more as a child of US 25 (another 2dus without any 3dus routes) than as US 21's.

Though some of those 3dus could be turned into a 2dus. White-out the last 2 in US 322, and you get US 32!

A number of these relate to extensions and decommissioning over the years. To cite your examples, there have been past incarnations of US 106, US 140, and US 240, that have been decommissioned. And US 206 only reached its parent due to a short concurrency with US 209, whereby US 206 ended but US 209 continued concurrent with US 6.

US 21 used to extend all the way north to Cleveland, but was decommissioned in stages as I-77 was completed. It was mostly concurrent with other routes (US 52, US 19, US 60) from Wytheville to Charleston. So while US 121 comes close to intersecting its former parent (the designation will probably end at the WV Turnpike, short of meeting what was US 21 in Beckley) a more appropriate number would be an X23 or even an x60, since it will intersect US 460.

As for US 421, it has undergone several extensions over the years. On Facebook the other day, someone (believe it was Chris Curley) posted a newspaper story mentioning the extension of US 421 from Bristol through SW Virginia and into Kentucky. The extension across the river and into Indiana came later.

I checked USends, and the original routing was between Boone and Greensboro, and US 21 was the only 2dus it intersected, so an x21 would make sense now that I think about it. If I would change something with what I wrote in the op, I said that US 421 would be better off as an x25, but an x52 would be even better if it could be renumbered. Roughly the same NW-SE trajectory, and meets US 52 twice, in Indianapolis and Winston-Salem.

Unrelated to the thread, though something else interesting I found out about US 21. USends list out the length of each US route at its peak, and despite being an x1 (primary odd numbered routes in the US routes system), its neighboring routes are longer than US 21.

US 21: 830 mi

US 19: 1365 mi
US 23: 1412 mi, though US 23's southern terminus initially was in Portsmouth, OH.
US 25: 1116 mi, including decommissioned section north of Cincinnati.
US 27: 1718 mi, including decommissioned section north of Ft Wayne. Its southern terminus was initially in Cincinnati.

[SEWIGuy]

It's whatever the people in charge felt like. No real rhyme or reason.

That's not the case at all.  When the system was laid out, 3dus highways were largely assigned from north to south for odd routes, and east to west for even routes.  The reason they no may no longer seem logical is due to the types of changes that hbelkins points out.

[Roadgeekteen]

It's whatever the people in charge felt like. No real rhyme or reason.

That's not the case at all.  When the system was laid out, 3dus highways were largely assigned from north to south for odd routes, and east to west for even routes.  The reason they no may no longer seem logical is due to the types of changes that hbelkins points out.

There are so many exceptions that the even/odd rule is no longer relevant in the modern day. It maybe used to be relevant.

[Flint1979]

They go in order starting with 1 and going up. So like US-127 is the first spur of US-27 and then the second one would be US-227 and so on.

No, the question wasn't "why is US-127 not US-227", it's "why is US-127 not US-125" (or any other N-S 2di it intersects).

The 3dus numbering rules are quite a bit more loosey-goosey than 3di numbering rules, probably because they have to maintain at least a token attempt at direction parity while 3dis don't (you can have an east-west 3di with a north-south parent route). I'm pretty sure what they did on most of them was just try to identify which of the intersecting 2duses the 3dus most closely shadows in terms of corridor, and then went with that. But it's been almost 100 years since the system was established, and exceptions abound, especially since so many routes have been extended and cut back several times throughout their history.

Oh ok I didn't read the question right. I'd imagine it depends on the route.

[US 89]

They go in order starting with 1 and going up. So like US-127 is the first spur of US-27 and then the second one would be US-227 and so on.

This isn't even true, though that was how it was when they were first laid out. See US 491.

[Rothman]

They go in order starting with 1 and going up. So like US-127 is the first spur of US-27 and then the second one would be US-227 and so on.

This isn't even true, though that was how it was when they were first laid out. See US 491.

Given that 491 replaced 666 very late in the game, it represents an exception rather than the rule.

...although I am not sure the rule mentioned was really followed.  Just saying out of examples to show it wasn't, 491 isn't a great one.

[hotdogPi]

They go in order starting with 1 and going up. So like US-127 is the first spur of US-27 and then the second one would be US-227 and so on.

This isn't even true, though that was how it was when they were first laid out. See US 491.

Given that 491 replaced 666 very late in the game, it represents an exception rather than the rule.

...although I am not sure the rule mentioned was really followed.  Just saying out of examples to show it wasn't, 491 isn't a great one.

If 4xx exists or existed, that means 1xx, 2xx, and 3xx exists or existed. The same is true for other digits. There are only three exceptions: 400, 425, and 491, and the first two aren't meant to be x00 or x25 routes.

[SkyPesos]

They go in order starting with 1 and going up. So like US-127 is the first spur of US-27 and then the second one would be US-227 and so on.

This isn't even true, though that was how it was when they were first laid out. See US 491.

Given that 491 replaced 666 very late in the game, it represents an exception rather than the rule.

...although I am not sure the rule mentioned was really followed.  Just saying out of examples to show it wasn't, 491 isn't a great one.

If 4xx exists or existed, that means 1xx, 2xx, and 3xx exists or existed. The same is true for other digits. There are only three exceptions: 400, 425, and 491, and the first two aren't meant to be x00 or x25 routes.

412? I doubt anyone consider 412 a child route of US 12.

[hotdogPi]

If 4xx exists or existed, that means 1xx, 2xx, and 3xx exists or existed. The same is true for other digits. There are only three exceptions: 400, 425, and 491, and the first two aren't meant to be x00 or x25 routes.

412? I doubt anyone consider 412 a child route of US 12.

Despite not being a child route, 112, 212, and 312 all exist or existed previously.

[Flint1979]

They go in order starting with 1 and going up. So like US-127 is the first spur of US-27 and then the second one would be US-227 and so on.

This isn't even true, though that was how it was when they were first laid out. See US 491.

As originally designed the first digit of the spurs increased from north to south and east to west along the parent. Using US-491 which replaced US-666 18 years ago isn't that good of an example btw. US-491 is a child of US-91 via it's connection with US-191 in Monticello, Utah. The reason that US-291 and US-391 were not used is because they were already state highway numbers in at least one of the affected states. US-666 was the correct number for US-66's spurs since it was the sixth spur along US-66.

[Flint1979]

They go in order starting with 1 and going up. So like US-127 is the first spur of US-27 and then the second one would be US-227 and so on.

This isn't even true, though that was how it was when they were first laid out. See US 491.

Given that 491 replaced 666 very late in the game, it represents an exception rather than the rule.

...although I am not sure the rule mentioned was really followed.  Just saying out of examples to show it wasn't, 491 isn't a great one.

If 4xx exists or existed, that means 1xx, 2xx, and 3xx exists or existed. The same is true for other digits. There are only three exceptions: 400, 425, and 491, and the first two aren't meant to be x00 or x25 routes.

412? I doubt anyone consider 412 a child route of US 12.

The problem I have with US-412 is that it overlaps several other US highways and has an out of grid number since it comes nowhere near US-12. So nope this one isn't a child route but I think it should be a 2du instead of a 3du.

[SkyPesos]

They go in order starting with 1 and going up. So like US-127 is the first spur of US-27 and then the second one would be US-227 and so on.

This isn't even true, though that was how it was when they were first laid out. See US 491.

Given that 491 replaced 666 very late in the game, it represents an exception rather than the rule.

...although I am not sure the rule mentioned was really followed.  Just saying out of examples to show it wasn't, 491 isn't a great one.

If 4xx exists or existed, that means 1xx, 2xx, and 3xx exists or existed. The same is true for other digits. There are only three exceptions: 400, 425, and 491, and the first two aren't meant to be x00 or x25 routes.

412? I doubt anyone consider 412 a child route of US 12.

The problem I have with US-412 is that it overlaps several other US highways and has an out of grid number since it comes nowhere near US-12. So nope this one isn't a child route but I think it should be a 2du instead of a 3du.

Yea, this is why I think the 68 number should've been used on current US 412, and not wasted on a route that feels and acts like a 3dus child route of US 62.

And a bit unrelated, is there a state that have more 2dus routes signed in its perpendicular direction than Ohio? There's 33 and 35 signed E-W, 42 and 68 signed N-S here. Not sure if 62 is also signed N-S south of Columbus, but it definitely runs that way.

[Flint1979]

They go in order starting with 1 and going up. So like US-127 is the first spur of US-27 and then the second one would be US-227 and so on.

This isn't even true, though that was how it was when they were first laid out. See US 491.

Given that 491 replaced 666 very late in the game, it represents an exception rather than the rule.

...although I am not sure the rule mentioned was really followed.  Just saying out of examples to show it wasn't, 491 isn't a great one.

If 4xx exists or existed, that means 1xx, 2xx, and 3xx exists or existed. The same is true for other digits. There are only three exceptions: 400, 425, and 491, and the first two aren't meant to be x00 or x25 routes.

412? I doubt anyone consider 412 a child route of US 12.

The problem I have with US-412 is that it overlaps several other US highways and has an out of grid number since it comes nowhere near US-12. So nope this one isn't a child route but I think it should be a 2du instead of a 3du.

Yea, this is why I think the 68 number should've been used on current US 412, and not wasted on a route that feels and acts like a 3dus child route of US 62.

And a bit unrelated, is there a state that have more 2dus routes signed in its perpendicular direction than Ohio? There's 33 and 35 signed E-W, 42 and 68 signed N-S here. Not sure if 62 is also signed N-S south of Columbus, but it definitely runs that way.

I can vouch for that. US-68 is more less a N-S highway maybe not so much in Kentucky but it is in Ohio.

For the second part of your post, I was in Ohio yesterday and wondering the same thing and the idea came upon when I intersected US-42 in Mason I thought it's strange seeing an even numbered highway going N-S and then thought well Ohio is known for this with US-68, US-35, US-33 and so on.

[Hot Rod Hootenanny]

And a bit unrelated, is there a state that have more 2dus routes signed in its perpendicular direction than Ohio? There's 33 and 35 signed E-W, 42 and 68 signed N-S here. Not sure if 62 is also signed N-S south of Columbus, but it definitely runs that way.

Ohio used to sign some of their angled routes with N-West, S-East, etc.
Even after ODOT stopped doing that, they still had trouble deciding on which direction routes would go.