Picking parents for 3dis

[Rothman]

Also - the same goes for NC I-587. Why not I-187, I-387, I-787, I-987? None of those exist anywhere, except I-787 near Albany, NY - and that's a separate I-87 system altogether.

There's an I-587 in Kingston NY, though it's a pretty short glorified ramp that ends at roundabouts on both sides. Imo it's fine as just NY 28.

NYSDOT takes the 90% fed share on it, thank you very much.

[sprjus4]

^ Maybe the better word would've been an unsigned interstate. Which, it basically already is, save a couple signs.

[hbelkins]

587 in New York would be a better candidate for being unsigned than 595 in Maryland, in my opinion. Last time I was there, 587 isn't even signed on 87.

[JoePCool14]

I wonder this too. Like why is our loop in Houston interstate 610 and not interstate 245 or 445? Why is San Antonio's interstate 410 and not 435 or even 437 or 837?

In those cases, 410 and 610 roll off the tongue better than 435 or 837. Human preference plays a part there.

I've never noticed anyone in Kansas City having any problem rolling 435 off their tongue.

Yep, I've never seen a problem with the other notable xx5 beltways "not rolling off their tongue" over an xx0 (I-465, I-275, I-495 to name a few)

I've never had an issue with any given number not rolling off the tongue. Some numbers are more fun to say (Route 66, for example). None of them are hard to say and I don't think that was really reasoning for why a number was or wasn't chosen. But it's an interesting idea at the very least.

Maybe rolling off the tongue wasn't the right way to say it. But it's the number of syllables, shortens how long it takes to say. Saying 410 is faster than 435. It's not that important.

But I also think retaining existing numbers is more important than renumbering something to a 3di, especially nowadays.

I disagree. I think we should still try to keep the system in order for the long-term. Better consistency across the country.

[HighwayStar]

I disagree. I think we should still try to keep the system in order for the long-term. Better consistency across the country.

I wholeheartedly agree. The point of a numbering system is to encode information about the routes into their names to assist the users of the road.
Fortunately the interstate system is not too badly mangled yet, and with relatively minor adjustments it should be possible to keep things consistent.
The US highways are a prime example of what not to do, allowing deviations to accumulate over time you end up with a spaghetti network.

The only issue as far as numbering 3 digits comes up if there is a shortage of numbers in a given state on a given route. 1,3,5,7,9 give 5 spur numbers per state per route, and 2,4,6,8 gives 4 loop numbers. Are there any interstates where this has yet become a problem? California or Texas seem like potential problems, being large and with many urban areas.

[JoePCool14]

The only issue as far as numbering 3 digits comes up if there is a shortage of numbers in a given state on a given route. 1,3,5,7,9 give 5 spur numbers per state per route, and 2,4,6,8 gives 4 loop numbers. Are there any interstates where this has yet become a problem? California or Texas seem like potential problems, being large and with many urban areas.

Yes, I-80 in California is maxed out.

[SkyPesos]

Some states like to use even first digit 3di numbers on any route that connects two interstates, while others only use even first digits on those that connect the parent interstate twice. It seems more likely for states in the former category to max out the 3di numbers, as they really only have 4 numbers per 2di to work with instead of 9 if none or very few of their 3di routes are "dead-end" (relative to the interstate system, can't think of a better word) spurs.

[Roadgeekteen]

The only issue as far as numbering 3 digits comes up if there is a shortage of numbers in a given state on a given route. 1,3,5,7,9 give 5 spur numbers per state per route, and 2,4,6,8 gives 4 loop numbers. Are there any interstates where this has yet become a problem? California or Texas seem like potential problems, being large and with many urban areas.

Yes, I-80 in California is maxed out.

I-180 is not in use, although they would have to renumber CA 180.

[WillWeaverRVA]

The only issue as far as numbering 3 digits comes up if there is a shortage of numbers in a given state on a given route. 1,3,5,7,9 give 5 spur numbers per state per route, and 2,4,6,8 gives 4 loop numbers. Are there any interstates where this has yet become a problem? California or Texas seem like potential problems, being large and with many urban areas.

Yes, I-80 in California is maxed out.

I-180 is not in use, although they would have to renumber CA 180.

I-480 is also not in use, and there hasn't been a CA 480 since the Embarcadero Freeway was destroyed in 1989 and decommissioned in 1991. You'd think they could just number I-238 to I-480, but I-480 remains a sore subject in the Bay Area to this day.

[HighwayStar]

Some states like to use even first digit 3di numbers on any route that connects two interstates, while others only use even first digits on those that connect the parent interstate twice. It seems more likely for states in the former category to max out the 3di numbers, as they really only have 4 numbers per 2di to work with instead of 9 if none or very few of their 3di routes are "dead-end" (relative to the interstate system, can't think of a better word) spurs.

The latter states are doing it correctly. The benefit of using the second definition is they have clearly defined a true "loop", ie, if I as a motorist see I-470 coming up I know that it will bring me back to I-70 after we bypass whatever town it is. And as you point out this conserves numbers for other routes.

[Quillz]

I was under the impression all that matters is the parent. So a "spur" can connect two interstates as long as it's the parent on one side and another one on the other side.

California ran out of x80 and did use most of them "correctly"

205: incorrect, only touches 5 at one end. could be "fixed" by numbering this one 305, 705, 905. the former and latter are in use (technically, neither are signed), 705 has never been assigned.

405: correct, begins and ends at the 5

605: incorrect, only touches 5 at one end. could again be "fixed" by using 305, 705, 905. but already running into an issue because there aren't enough numbers, assuming spur is being used strictly to refer to only touching its parent once.

805: correct, begins and ends at the 5

280: never meets 80, was supposed to junction with 480, in either case, this would make it more a spur. so 180, 380, 580, 780, 980. which is another issue because 380, 580, 780, 980 are all used "correctly" in the sense they touch their parent once.

So California was bound to run out even if all were being applied properly. This is also one of the reasons why I think the interstate design standards were more important, and completely replacing one state highway number with an interstate number wasn't always the best idea. I would have been in favor of keeping something like CA-21 or CA-35 intact and allowed those 3di numbers be used elsewhere. Another possibility was combining 280 and 680 into something of a half-loop, not quite a beltway but a similar concept.

New York is the only state I know of that presently has used up all available 3di, as there is Interstates 190-990.

[TheStranger]

IIRC, all the even first digit means is that the route is supposed to meet up with Interstates at both ends, regardless of parent.

205: incorrect, only touches 5 at one end. could be "fixed" by numbering this one 305, 705, 905. the former and latter are in use (technically, neither are signed), 705 has never been assigned.

1. At one point, this was supposed to connect what was I-5W (now I-580) and what was the 1958-1964 I-5E proposal (now I-5), so that would have technically been both ends at parent.

2. Both ends are at Interstates.

605: incorrect, only touches 5 at one end. could again be "fixed" by using 305, 705, 905. but already running into an issue because there aren't enough numbers, assuming spur is being used strictly to refer to only touching its parent once.

As noted in the post I did earlier - https://www.aaroads.com/forum/index.php?topic=33145.msg2834973#msg2834973 - 605 as originally proposed linked I-10 (one interstate) with I-405 (another interstate).  It isn't a loop/bypass, but it does have Interstates at both ends.  (I guess it could be seen as I-10 traffic bypassing downtown LA to get to Long Beach and Orange County)

280: never meets 80, was supposed to junction with 480, in either case, this would make it more a spur. so 180, 380, 580, 780, 980.

Also mentioned in my earlier post: I-80 was originally planned to terminate at I-280 in Golden Gate Park, prior to the freeway revolts of the 1960s (which caused the cancellation of freeway construction along the 19th Avenue/Junipero Serra corridor past Font Boulevard, and nixed the I-80 Western Freeway entirely from the Central Freeway/Fell Street junction west along the Panhandle park corridor).

After 1968, I-280 was rerouted along former US 101 (Southern Freeway) and one-time proposed Route 87 (along the section from Cesar Chavez (Army) to I-80/Route 480, though only the part to 3rd Street was ever built.  The portion from 6th to 3rd was rebuilt as King Street in conjunction with the opening of the Giants' new stadium in 2000.

280 in its 1968-present definition was supposed to have termini at I-80 near Fremont Street, and its current southern terminus at I-680/US 101 (so there is a link to another interstate there).

I can see why 280/680 are separate numbers, for similar reasons as 494/694 in Minneapolis - the two halves of the belt are too distinct rather than square/circular.

[HighwayStar]

I was under the impression all that matters is the parent. So a "spur" can connect two interstates as long as it's the parent on one side and another one on the other side.

California ran out of x80 and did use most of them "correctly"

205: incorrect, only touches 5 at one end. could be "fixed" by numbering this one 305, 705, 905. the former and latter are in use (technically, neither are signed), 705 has never been assigned.

405: correct, begins and ends at the 5

605: incorrect, only touches 5 at one end. could again be "fixed" by using 305, 705, 905. but already running into an issue because there aren't enough numbers, assuming spur is being used strictly to refer to only touching its parent once.

805: correct, begins and ends at the 5

280: never meets 80, was supposed to junction with 480, in either case, this would make it more a spur. so 180, 380, 580, 780, 980. which is another issue because 380, 580, 780, 980 are all used "correctly" in the sense they touch their parent once.

So California was bound to run out even if all were being applied properly. This is also one of the reasons why I think the interstate design standards were more important, and completely replacing one state highway number with an interstate number wasn't always the best idea. I would have been in favor of keeping something like CA-21 or CA-35 intact and allowed those 3di numbers be used elsewhere. Another possibility was combining 280 and 680 into something of a half-loop, not quite a beltway but a similar concept.

New York is the only state I know of that presently has used up all available 3di, as there is Interstates 190-990.

A potential solution, though awkward and possibly problematic would be to allow the use of 2 digit lead digits, ie 1190, 1290, etc.
In any case, I don't think the interstate was as well provisioned with auxiliary route options as the US numbered system.

Although it was not exactly planned this way and violates it in many cases, the US numbered system in theory has the parent route, 1 or 2 digit, and up to 9 three digit spur routes from the parent route available.
Loops are effectively unlimited, and better yet can be made descriptive by using Bypass, Alternate, Loop, City, Business, Scenic, Truck, Toll, and Historic. Divided routes with cardinal designations add yet another variant to this.

[hotdogPi]

I believe it should be whether it's radial or circumferential. For example, I-291 in Connecticut is correct despite not meeting I-91 at both ends because it's a partial loop around Hartford, not inward or outward. On the other hand, I-270 in Maryland is incorrect because it clearly goes to and from DC.

[sprjus4]

How is I-270 incorrect? It connects with an interstate on either end.... I-70 (its parent to the north) and I-495 to south.

[hotdogPi]

It's the way to DC. It's not a loop or beltway around anything.

[HighwayStar]

How is I-270 incorrect? It connects with an interstate on either end.... I-70 (its parent to the north) and I-495 to south.

It must connect to the same interstate at both ends to make it a true loop. It should be a spur, hence numbered I-170 for example.

[sprjus4]

A 3di interstate highway can have an even digit if it connects to an interstate highway on both ends If I-270 terminated in the DC metro with no connection to I-495 or any other interstate highway, then an odd digit would be appropriate.

It connects to I-70 to the north and I-495 on the south. An even digit is perfectly appropriate.

[ilpt4u]

A 3di interstate highway can have an even digit if it connects to an interstate highway on both ends If I-270 terminated in the DC metro with no connection to I-495 or any other interstate highway, then an odd digit would be appropriate.

It connects to I-70 to the north and I-495 on the south. An even digit is perfectly appropriate.

Illinois tends to deploy the "Odd"  first digit in cases of only touching the parent once, regardless if both ends are Interstates or not

I-155 has one end on 55 and the other on 74
I-355* has one end on 80 and the other on 290. Former southern end was 55

I-190 has one end on 90 and the other at ORD airport
I-180 has one end on 80...the other a lot of nothing
I-172 has one end on 72 and one end on IL 110/336

When the I-490 Tollway is completed and signed, it will be the first "Even"  first digit 3di in IL that only touches its parent once

I-355 was proposed, and maps were even printed before before its opening, of it getting the I-455 designation, but obviously that did not happen

[I-55]

Another unusual example that I realized today: Why is I-576 in Pittsburgh an x76 instead of an x79? Yes, I know it meets I-376, but it doesn't meet I-76 itself, while it does meet I-79. Shouldn't that alone make an x79 number better than an x76? Also, it's north-south, which parallels with I-79 more.

My best guess would be that Pennsylvanians tend to associate 76 with toll roads, so 576 fits right in with 276, 376, and 476, all of whom are tolled or have tolled segments. I-79 is free for its entirety as well.

[GaryA]

In Southern California,  I-605 and I-710 are essentially parallel freeways, both initially proposed as extending from I-10 southward (605 was later extended north; 710 was planned to be extended north, later cancelled).

Yet why is one an I-x05 and the other an I-x10?  If one wanted to maintain a mnemonic link between CA-7 and its replacement, I-705 was just as available as I-710.  (And 610 available instead of 605, unless someone wanted to reserve that for a potential CA-60 renumbering.)

As for why one was a "loop" and the other a "spur",  both ends of I-605 are at another interstate (I-10 initially, I-210 currently to I-405), but the south end of I-710 has always extended into Long Beach and does not end at another Interstate.

[TheStranger]

As for why one was a "loop" and the other a "spur",  both ends of I-605 are at another interstate (I-10 initially, I-210 currently to I-405), but the south end of I-710 has always extended into Long Beach and does not end at another Interstate.

Interestingly, the 1963-1965 definiton of Route 7 included what is now Route 47 between the Harbor and Terminal Island Freeways - by the time I-710 was designated, I-110 already existed on the Harbor Freeway, but that middle segment between San Pedro and 47/103 is still not full freeway to this day (with the one remaining intersection at Navy Avenue).

The configuration of I-710 at Route 47 along Seaside has 47 exiting itself and 103 and 710 each beginning from that spot, with 103 following 47 from the diamond interchange ramps north to the Terminal Island Freeway.  Basically, the through lane configuration today has a number change, but would have fit the 1963-1965 definition of Route 7.

[Henry]

A thought just occurred to me: In a perfect world, I-4 would have some 3di's in Orlando, but the 4xx toll roads there make it appear as though they could be adopted by it. Which, as it is, could also qualify as a route numbering coincidence.

[jdbx]

I've never had an issue with any given number not rolling off the tongue. Some numbers are more fun to say (Route 66, for example). None of them are hard to say and I don't think that was really reasoning for why a number was or wasn't chosen. But it's an interesting idea at the very least. But I also think retaining existing numbers is more important than renumbering something to a 3di, especially nowadays. In the early days this probably made sense as a way to promote the system, but now the design standards and funding are more important. (And I don't think the latter is even a thing anymore). In the case of California, if they could do it over, I'd say just don't even bother with I-238. Just leave it as CA-238, or just keep the whole thing as CA-9 (which it originally was anyway).

An important point to remember is that I-238 carries a significant volume of truck traffic due to the ban on big rigs on I-580 through Oakland. I believe part of the stated reason for having an interstate designation was to convey to long-distance truck traffic, particularly in the era before GPS, that this was a high-quality interestate-grade connector and not just any old state highway.  That Interstate shield conveys certain expectations for a highway that a state or US shield does not.

[roadfro]

What I find interesting is states that have few 3di, not always choosing the lowest available. Like in Nevada, it was I-515 as opposed to either I-115 or I-315. On one hand you could argue this was perhaps due to planned future expansion, but Las Vegas is in the southeast corner of the state, the odds of either a 115 or 315 showing up farther south seems pretty slim. The odd number makes sense given odd leading digits are usually used as spurs, but I've always wondered where that number came from.

I've always speculated that Nevada using 515 and 580 instead of lower available spur numbers has to do with how the state route numbers were assigned in the 1976 renumbering–both interstates being in various planning stages at the time of the renumbering. Routes numbers in the 500 and 600 series were assigned to urban routes (FAU funding scheme), so assigning numbers beginning with "5" to these urban interstate spurs made sense. (Had 515 and 580 not been assigned to interstate spurs, they would have been assigned to roads in a different part of the state, based on the number clustering model adopted during the renumbering. A hypothetical SR 515 would have been assigned to a road in Carson City, and a hypothetical SR 580 would likely have been located along an east/west section line arterial in the Las Vegas area.

Also, Nevada doesn't use the same number in different systems. An SR 115 was assigned near Fallon during the renumbering, and while I don't think an SR 315 (or FAP 315) was ever assigned, "315" likely fell in the "gap for future expansion" between numbers assigned in Lander and Lincoln counties.