3dis vs 2dis

[Zeffy]

You know, I always thought di stood for digits not interstates.

I used to as well... but then someone mentioned '2dus' and I knew then that 'di' was 'x digit Interstate'. But what is a state route? 2dsr? Sounds odd.

[Molandfreak]

No. di stands for digit. Digit Interstate is for anal roadgeeks.

[vdeane]

Digit interstate seems to be the convention here.  I don't know that 2/3dsr would ever come up.  Are there states that use 3 digit routes as children of 1/2 digit routes?

[hotdogPi]

Digit interstate seems to be the convention here.  I don't know that 2/3dsr would ever come up.  Are there states that use 3 digit routes as children of 1/2 digit routes?

MA does for 203. These types of routes are not very common, though.

[Kacie Jane]

Digit interstate seems to be the convention here.  I don't know that 2/3dsr would ever come up.  Are there states that use 3 digit routes as children of 1/2 digit routes?

Washington.  Don't think that there are any others (save for special cases), but in several states, 3dsr's are definitely the more minor routes, even if they aren't numbered as spurs of parents.

[bulldog1979]

You know, I always thought di stood for digits not interstates.

I used to as well... but then someone mentioned '2dus' and I knew then that 'di' was 'x digit Interstate'. But what is a state route? 2dsr? Sounds odd.

The way I learned it was "2dI" with the I capitalized for "two-digit Interstate" along with "2dUS" for "two-digit US Highway". In referring to Michigan, I will use "1dM", "2dM" and "3dM" to refer to the state highways with the appropriate number of digits, usually in the context of discussing signage. (3dMs almost never have any connection to another highway, although M-120, M-121, M-227 and M-331 were formerly parts of M-20, M-21, US 27 and US 131, respectively and M-231 is supposed to be part of US 31 someday.)

[getemngo]

Another reason a lot of us believe "3di" means "3-digit Interstate" is that's what Kurumi's site taught us many years ago.

The way I learned it was "2dI" with the I capitalized for "two-digit Interstate" along with "2dUS" for "two-digit US Highway". In referring to Michigan, I will use "1dM", "2dM" and "3dM" to refer to the state highways with the appropriate number of digits, usually in the context of discussing signage. (3dMs almost never have any connection to another highway, although M-120, M-121, M-227 and M-331 were formerly parts of M-20, M-21, US 27 and US 131, respectively and M-231 is supposed to be part of US 31 someday.)

Not to mention that there are some 3-digit highways in Michigan that are not former alignments of their 2-digit equivalent, and may not even touch them, but they're still implied "child" routes, such as M-179 and M-199.

Some of Hawaii's 3-digit routes are related to its 2-digit routes, but they tend to be multiply the 2-digit route by 10 (e.g. 310 is related to 31, and 360 is related to 36).

It's really weird that there don't appear to be any topics on AARoads specifically about 3 digit state highways.

[Alps]

2dsr and 3dsr are indeed proper terminology. It's useful in NJ, where most of the 3dsr are minor and most of the 2dsr are major.

[Ned Weasel]

Digit interstate seems to be the convention here.  I don't know that 2/3dsr would ever come up.  Are there states that use 3 digit routes as children of 1/2 digit routes?

I thought this was common.  It's at least not uncommon to have a 3DSR child of a higher-species parent.  Examples:

K(S)-150 (Child of US 50)
MO 150 (Another child of US 50)
MO 249 (Child of I-49)
MO 370 (Child of I-70)
IL 255 (Numerically, this is a child of I-55, although this example is debatable, since it is really a state-route continuation of I-255, and 255 only intersects with I-55 when it is in Interstate form.)

Kansas has a couple of would-be children that never quite meet the parent route (and I'm not sure whether they ever did, so I'm not sure they count as orphans).  K-177 is close to meeting US 77 at both ends, and is only one connecting route away in both cases.  K-196's eastern terminus is at K-254, which connects to K-96 and is (of course) a child of US 54.

[hbelkins]

No. di stands for digit. Digit Interstate is for anal roadgeeks.

Wrong.

The way I learned it was "2dI" with the I capitalized for "two-digit Interstate" along with "2dUS" for "two-digit US Highway".

Right. Sorta. I never capitalized the I or US.

[PurdueBill]

Digit interstate seems to be the convention here.  I don't know that 2/3dsr would ever come up.  Are there states that use 3 digit routes as children of 1/2 digit routes?

Indiana does (or used to more); the recently-deleted 443, 126, and 526 in West Lafayette are examples. 

Not every 3-digit route in Indiana is a child route this way necessarily though.

[Henry]

The way I learned it was "2dI" with the I capitalized for "two-digit Interstate" along with "2dUS" for "two-digit US Highway".

Right. Sorta. I never capitalized the I or US.

If you must capitalize, then at least make it consistent, like 2DI, 3DI, 2DUS and 3DUS.

[Kacie Jane]

The way I learned it was "2dI" with the I capitalized for "two-digit Interstate" along with "2dUS" for "two-digit US Highway".

Right. Sorta. I never capitalized the I or US.

If you must capitalize, then at least make it consistent, like 2DI, 3DI, 2DUS and 3DUS.

If you look at the way bulldog spelled out the terms, it is in fact consistent, just in a different way. (That said, I prefer the all lowercase versions.)

[agentsteel53]

MA does for 203. These types of routes are not very common, though.

rare in California as well.  107 is the old alignment of 7, and at one point (1940-1957) served as a child route, branching off the parent.

[jeffandnicole]

Digit interstate seems to be the convention here.  I don't know that 2/3dsr would ever come up.  Are there states that use 3 digit routes as children of 1/2 digit routes?

As Steve Alps said, NJ does, although not always, and it's not perfectly consistent with Interstate highway rules.

47 has 147 & 347.  Interstate Highway rules would say they're both spurs off of 47.  147 meets that definition, but 347 is simply a loop (or really, a shortcut) which meets up with 47 on both ends.

68 has nothing to do with 168.

[mrsman]

It's an artifact of the FHWA's insistence that 3di loop exit numbering starts at the south end of the loop.  I-465 should start at I-65 near Zionsville and go all the way around east, south, west, and then back north to what is currently I-865.  That would remove any confusion without the added 3di.

that implies a Q-shaped interstate.  I would not want to be the one tasked to design quickly comprehensible signage at the 465-465-465 junction.

Heading north:

TO {65} NORTH     {465} EAST
Chicago

Heading west:

TO {65} NORTH     {465} SOUTH
Chicago

Heading east:

{465} EAST          {465} SOUTH

Not too difficult.  I-865 is unnecessary.

Sorry to chime in to the discussion on the late side, but there's a similar situation near me, with the exception that the interstate isn't circumferential.

I-270 runs from Frederick, MD to Bethesda, MD.  It used to be I-70S.  I-70S ran into the Beltway heading east and a spur route known as I-270 connected I-70S to the Beltway going in the other direction towards Fairfax County, VA.

When interstate suffixes were dropped I-70S was renamed I-270.  The old I-270 spur became what is known as the I-270 SPUR.  Northbound it is signed as I-270 North (sometimes with a "TO" designation.  Southbound it is signed as TO I-495 SOUTH (sometimes with a "SPUR I-270" designation as well.  I-270 spur even has one exit between the I-270 mainline and the Beltway at Democracy Blvd.

It seems that Indiana could've done something similar as you mentioned above.  Control cities for the beltway would also help.

[english si]

In the UK, we've always used 3da and 4da as short hand for three- and four-digit A roads, despite no child/parent link.

[TheStranger]

MA does for 203. These types of routes are not very common, though.

rare in California as well.  107 is the old alignment of 7, and at one point (1940-1957) served as a child route, branching off the parent.

330, 242, and 371 are the only others in California that derive their numbering from the former routes that they took over (though 242 is somewhat debatable as it also fits a relative geographic cluster that includes 237, 238, unbuilt 239 and the 1965-1968 241.)

Are there any true "parent route" type things other than 330 (which, until the 210/30 switchover, did connect to 30)? 

[FightingIrish]

Is it just me, or does it drive any of you crazy when a 3di is longer than it's 2di, such as US 191 & US 91?

Back to the original post, many years ago (as most here already know), most of US 91 was decommissioned, particularly in California (where it is now either CA 91 or I-15)  and Nevada. The current US 91 is currently a shell of its former self. Meanwhile, US 191 has been rerouted and lengthened many times. One reason it has lasted so libg is that it hasn't been mostly replaced by an interstate.

The concept of 3DUs has always been different than the philosophy of 3DIs. 3DUs simply branch off from the mother route (or another 3DU sibling) and go off in whatever directions they go. They were never intended to be alternate spur or bypass routes in metro areas.

The way that much of the US route system has been displaced by interstates has upset the cart a bit with naming conventions. That is unavoidable.

[kurumi]

"3di" = 3-digit interstate. (That term and "volleyball interchange" are my neologisms that for better or worse have found traction.)

[Arkansastravelguy]

Is it just me, or does it drive any of you crazy when a 3di is longer than it's 2di, such as US 191 & US 91?

I hate when the parent 2dus dies and poor 3dus left (US166, among others). Or Adopted 3dus with no parents (US400 and US412). Or perhaps 412 has a long distance relationship with its parent, they just don't meet (like US 311)


iPhone

[Alex4897]

Digit interstate seems to be the convention here.  I don't know that 2/3dsr would ever come up.  Are there states that use 3 digit routes as children of 1/2 digit routes?

As Steve Alps said, NJ does, although not always, and it's not perfectly consistent with Interstate highway rules.

47 has 147 & 347.  Interstate Highway rules would say they're both spurs off of 47.  147 meets that definition, but 347 is simply a loop (or really, a shortcut) which meets up with 47 on both ends.

68 has nothing to do with 168.

Delaware has 41 with 141 as its child. Otherwise, all other 3 digit routes were carried over from other states.

[Scott5114]

Digit interstate seems to be the convention here.  I don't know that 2/3dsr would ever come up.  Are there states that use 3 digit routes as children of 1/2 digit routes?

I thought this was common.  It's at least not uncommon to have a 3DSR child of a higher-species parent.

Similarly, Oklahoma has lettered spur routes of US routes, although none exist of interstates (SH-40A is numbered after the long-since-renumbered SH-40, and SH-44A is numbered after the extant SH-44).

[jbnv]

US 165 traverses two major cities in Louisiana and almost reaches a third. US 65 passes through the people- and money-poor delta en route to Natchez.

There's no excuse for US 400, 412 and 425 (which well could have been US 265).

[flowmotion]

The concept of 3DUs has always been different than the philosophy of 3DIs. 3DUs simply branch off from the mother route (or another 3DU sibling) and go off in whatever directions they go. They were never intended to be alternate spur or bypass routes in metro areas.

I hate when the parent 2dus dies and poor 3dus left (US166, among others). Or Adopted 3dus with no parents (US400 and US412). Or perhaps 412 has a long distance relationship with its parent, they just don't meet (like US 311)

There's no excuse for US 400, 412 and 425 (which well could have been US 265).

I think the key to "letting it go" is to realize the entire 3dus system is pretty much arbitrary and useless.

Nobody would ever get on US191 and keep driving, hoping they would eventually hit US91. The roads had little relationship to each other beyond intersecting at some arbitrary point. 2dus routes are not "parents" and 3dus routes are not "children".

It would have been much better if there was an sensible system to the 3dus routes, say 1XX routes on the east coast and 9xx routes on the west. As it stands, the extra digit is meaningless to the traveller, so it might as well be something random like 425.