Why are there not 4 digit interstates?

[Duke87]

How would such a numbering system work? Granted, rules are meant to be broken and as such there are always violations, but generally, even numbered routes are loops and odd numbered routes are spurs (I know all know this; just repeating for the point of the question) - if such a numbering system would be implemented, what would be the new guidelines?

I seem to recall concocting a system for 4 digit interstates with the intent of assigning them to all freeway segments in the country that do not currently have an interstate designation. My system did something along the lines of assigning them in blocks of 100 state by state.

So for example, Delaware would get Interstates 1000-1099, Pennsylvania 1100-1199, New Jersey 1200-1299, etc., all the way through Hawaii getting 5900-5999, Puerto Rico getting 6000-6099, 6100-6999 not used, and numbers 7000+ assigned in sequential order if a state happens to need more than 100.

[michravera]

It would make more sense than repeating the 3-dis

With the exception of I-95 (and possibly 10, 80 and 90) no parent 2di goes through more than 10 states and certainly no 3di is duplicated in more than 10 states. It would be possible (administratively) to assign the first digit "1" to the second state to construct a particular 3di that is not contiguous to the 3di with the same number and then "2", "3", etc to the third, fourth, etc. Existing duplicated 3dis could be numbered in the reverse of the method for choosing numbers for other interstates, so that Washington would get the I-(0)x05s and Florida would get the  I-(0)x95s. I would suggest a small superscript for the first digits that are higher than "1", so I-²205 and I-⁷580 would be in California.

[GaryV]

Should Georgia not use State Road 369 because there's a State Road 369 in Florida? The same applies to 3dis....

Remember that the 3-digit US routes don't have duplication, unlike 3-digit Interstates.

Because a 3dus is just as good as a 2dus. It just means it's a branch of the parent route (mostly) but still follows the other rules for US highways.

[RobbieL2415]

Now--- here's an idea. Don't all jump down my throat at once:

Except for situations where the 3DI spans multiple states, why assign 3DIs at all? Why not just long the miles in the federal system so the states get funding but just sign them as SRs?

[_Simon]

It's important to note that for much of the interstates system's life, even the 2di's were very disjointed.   My own state had very few interstates completed end to end until the 70s and 80s, so people for decades were able to deal with a route number ending and a seemingly unrelated route with the same number starting somewhere else in the state.  All this before exit numbering and fancy mile markers, so the phantom continuity wasn't necessarily intuitive (unless hagstrom was gracious enough to draw a dotted line). 

SM-G930V

[Max Rockatansky]

Now--- here's an idea. Don't all jump down my throat at once:

Except for situations where the 3DI spans multiple states, why assign 3DIs at all? Why not just long the miles in the federal system so the states get funding but just sign them as SRs?

That's kind of what I had in mind above with just retaining the state route number but making the shield Interstate colors.  That would sure solve that I-238 debacle right quick.

[Duke87]

Now--- here's an idea. Don't all jump down my throat at once:

Except for situations where the 3DI spans multiple states, why assign 3DIs at all? Why not just long the miles in the federal system so the states get funding but just sign them as SRs?

Had some of the early planners had their way we might not have 3dis at all. Note that the original system plans did not have any 3 digit numbers, and only included a select few of today's 3dis as suffixed routes (e.g. NY I-190 as I-90N, KS I-135 as I-35W). If the plans were not modified we would have fewer urban freeways, since states would have been on the hook to pay for these loop and spur routes themselves.

3dis as a concept were created because planners in cities wanted to be able to take advantage of federal money to carry out their urban renewal visions. And indeed if you think about it it is rather odd that we have these relatively short highways of predominantly local utility included in the "interstate" system - they were tacked onto it because of politics.

[Rushmeister]

Hmmm... I'm trying to think of a 4-digit number that would look good on a route marker.....

Nope, sorry, I'm not coming up with anything.

[GaryV]

Now--- here's an idea. Don't all jump down my throat at once:

Except for situations where the 3DI spans multiple states, why assign 3DIs at all? Why not just long the miles in the federal system so the states get funding but just sign them as SRs?

Because you gotta have that RWB badging, or it's not a good road.  See I-99, I-74, I-2, I-41, ...

[Big John]

Hmmm... I'm trying to think of a 4-digit number that would look good on a route marker.....

Nope, sorry, I'm not coming up with anything.

[Quillz]

I think 4di would work fine if they followed the same "rules" as 3di and simply treated the 3di as a 2di.

i.e. if CA-90 was converted into an interstate, it would use I-405 as its parent and thus could be numbered something like I-1405. Or, if it somehow connected to I-405 on both ends, could be numbered something like I-2405.

[adventurernumber1]

I am honestly intrigued by the idea of four-digit interstates. I think that as states such as California and New York may start to have the need for more three-digit interstates in each state, and we run out of 3di numbers, four-digit interstates could be of use.

-more input coming-

[Henry]

While in theory this could work, I don't see it ever happening. And besides, not every freeway needs to have an I-shield slapped on it!

[vdeane]

I am honestly intrigued by the idea of four-digit interstates. I think that as states such as California and New York may start to have the need for more three-digit interstates in each state, and we run out of 3di numbers, four-digit interstates could be of use.

-more input coming-

On the other hand, California and New York aren't likely to designate any more interstates any time soon (aside from I-86 between Waverly and Binghamton, but that's already a future interstate).  If NY needs more x90 interstates, I-390 can always become an extension of I-99.

[kphoger]

Look at it this way:  if we removed all duplicate 3di numbers, then...

I-180 (IL)
I-180 (NE)
I-180 (PA)
I-280 (CA)
I-280 (IA)
I-280 (NJ)
I-280 (OH)
I-380 (CA)
I-380 (IA)
I-380 (PA)
I-480 (CA)
I-480 (IA)
I-480 (OH)
I-580 (CA)
I-580 (NV)
I-680 (IA)
I-680 (CA)
I-680 (OH)
I-780 (CA)
I-880 (CA)
I-980 (CA)

...could become...

I-180
I-280
I-380
I-480
I-580
I-680
I-780
I-880
I-990
I-1080
I-1180
I-1280
I-1380
I-1480
I-1580
I-1680
I-1780
I-1880
I-1980
I-2080
I-2180

[The Ghostbuster]

I think the prospect of 4-digit Interstates is ridiculous. The numbering system is fine with 1, 2, and 3-digits.

[slorydn1]

I think the prospect of 4-digit Interstates is ridiculous. The numbering system is fine with 1, 2, and 3-digits.

I agree...the system was designed to have duplicate 3di's and it is understood that the I-295 in FL and the I-295 in NC have nothing to do with each other other than the fact they share the same parent. Even non roadgeeks understand that and I have never known someone to have been confused by them.

[Aerobird]

3dis as a concept were created because planners in cities wanted to be able to take advantage of federal money to carry out their urban renewal visions. And indeed if you think about it it is rather odd that we have these relatively short highways of predominantly local utility included in the "interstate" system - they were tacked onto it because of politics.

While that is true, remember also that it's the National System of Interstate and Defense Highways. In some cases 3dis were intended for that purpose - either to bypass cities (both to allow for uncongested movement and so that there would still be a workable road through the area if the city center got nuked), to allow for traffic flow for civil defense, and to connect industries critical to the national defense interest to the system (this was why I-180 in Illinois was built).

[Rothman]

3dis as a concept were created because planners in cities wanted to be able to take advantage of federal money to carry out their urban renewal visions. And indeed if you think about it it is rather odd that we have these relatively short highways of predominantly local utility included in the "interstate" system - they were tacked onto it because of politics.

While that is true, remember also that it's the National System of Interstate and Defense Highways. In some cases 3dis were intended for that purpose - either to bypass cities (both to allow for uncongested movement and so that there would still be a workable road through the area if the city center got nuked), to allow for traffic flow for civil defense, and to connect industries critical to the national defense interest to the system (this was why I-180 in Illinois was built).

I think you're overstating the importance of the "defense" part of the Act.  That was more of a ploy by Eisenhower to get the funding and bill passed more than actually setting up highways to prioritize military movements, despite any lip service to the contrary. 

People have taken the idea that it was meant mainly for defense to absurd limits, like that idiotic rumor that interstates had to straighten out every-so-often to allow for emergency aircraft landings.

[dvferyance]

I do like the idea of avoiding duplication with 3 digit interstates whenever possible I-94 is a good example of this.
I-194 MI
I-294 IL
I-394 MN
I-494 MN
I-694 MN
I-794 WI
I-894 WI
No repeats throughout the states of it's route. But when all are used along the route then I am ok with repeats in different states. Four digits are too much.

[kkt]

Now--- here's an idea. Don't all jump down my throat at once:

Except for situations where the 3DI spans multiple states, why assign 3DIs at all? Why not just long the miles in the federal system so the states get funding but just sign them as SRs?

I like that idea!

[vdeane]

3dis as a concept were created because planners in cities wanted to be able to take advantage of federal money to carry out their urban renewal visions. And indeed if you think about it it is rather odd that we have these relatively short highways of predominantly local utility included in the "interstate" system - they were tacked onto it because of politics.

While that is true, remember also that it's the National System of Interstate and Defense Highways. In some cases 3dis were intended for that purpose - either to bypass cities (both to allow for uncongested movement and so that there would still be a workable road through the area if the city center got nuked), to allow for traffic flow for civil defense, and to connect industries critical to the national defense interest to the system (this was why I-180 in Illinois was built).

I think you're overstating the importance of the "defense" part of the Act.  That was more of a ploy by Eisenhower to get the funding and bill passed more than actually setting up highways to prioritize military movements, despite any lip service to the contrary. 

People have taken the idea that it was meant mainly for defense to absurd limits, like that idiotic rumor that interstates had to straighten out every-so-often to allow for emergency aircraft landings.

Especially since Eisenhower didn't want urban interstates; he wanted them to connect regions, not go through cities.  The urban miles got added by Congress to secure votes from urban representatives.

[FrCorySticha]

I do like the idea of avoiding duplication with 3 digit interstates whenever possible I-94 is a good example of this.
I-194 MI
...
No repeats throughout the states of it's route. But when all are used along the route then I am ok with repeats in different states. Four digits are too much.

Not quite. There is also an I-194 in Bismarck, ND. It's short and unsigned, but does exist. https://goo.gl/maps/RkK1joJcbEo

[cpzilliacus]

I think 4di would work fine if they followed the same "rules" as 3di and simply treated the 3di as a 2di.

i.e. if CA-90 was converted into an interstate, it would use I-405 as its parent and thus could be numbered something like I-1405. Or, if it somehow connected to I-405 on both ends, could be numbered something like I-2405.

I would see CA-90 being I-705 (since I don't think there is a I-705 or CA-705 either). But if there were no odd 3di route numbers available, why not I-1105?

[dvferyance]

I do like the idea of avoiding duplication with 3 digit interstates whenever possible I-94 is a good example of this.
I-194 MI
...
No repeats throughout the states of it's route. But when all are used along the route then I am ok with repeats in different states. Four digits are too much.

Not quite. There is also an I-194 in Bismarck, ND. It's short and unsigned, but does exist. https://goo.gl/maps/RkK1joJcbEo

Next to nobody knows about. There was a I-394 proposal in Michigan and an I-494 one in Illinios but neither happened.