Numbering of 3di interstates ... why not use the lowest digit available?

[KEVIN_224]

@ DUKE87: How convenient with I-684, huh? Despite the fact that over 95% of the road is in New York!

[kurumi]

@ DUKE87: How convenient with I-684, huh? Despite the fact that over 95% of the road is in New York!

There was still a conflict when the highway originally opened, as I-87. Connecticut was preparing to renumber CT 87 as 287 but was able to abandon that when I-87 changed numbers instead.

[jp the roadgeek]

States try to avoid having 2 of the same 3DIs in consecutive states or within 100 miles of each other along the mainline of 2DI's.   CT chose I-395 over I-195 to avoid confusion with the I-195 in RI/MA. At one point, I-195 was to be extended to I-295 in Johnston, RI, which at its closest point is less than 30 miles from I-395 in Killingly, CT. Also, I-395 goes into MA up to the Mass Pike, so there'd be some real confusion with 2 195's in MA unless the I-290 designation were carried south to the CT line.  Examples of x95's from south to north

195: FL, VA, NJ (PA), RI/MA, ME
295: FL, NC, VA/MD, DE/NJ, NY, RI/MA
395: FL, VA/DC, CT/MA, ME
495: MD/VA/DC, DE, NY, MA, ME
595:  FL, MD (hidden)
695: DC, MD, NY
795: FL (future), NC, MD
895: VA, MD, NY

The only real exception here would be the 695's, but the DC one was a recent addition.

[TheStranger]

The only real exception here would be the 695's, but the DC one was a recent addition.

As a signed route, yeah.  As an actual designation?  DC's I-695 has existed much longer:

http://en.wikipedia.org/wiki/Interstate_695_(Washington,_D.C.)

Of course, going back to Connecticut, its I-291 is not that far from the Massachusetts route of the same number.

[deathtopumpkins]

The only real exception here would be the 695's, but the DC one was a recent addition.

No it was not. It may have only recently been signed for the first time, but it's existed since 1958.

[triplemultiplex]

Some states are picky about not using the same number twice regardless of classification, so they let piddly state highways on the other side of the state guide their 3di selection.  Once upon a time, Wisconsin was one of these states.  Then we got I-39.  Now we want I-41.  We correctly abandoned that silly idea.  Interstates should always trump US and state highway numberings.

The I-94 spurs in Milwaukee seem to have been chosen from the high end to distinguish them from sorta nearby Chicago and it's I-294 and then-proposed I-494.

Wasn't there something about an AM radio station involved in Ft. Worth's I-820?

[english si]

I-41/US41 is the same route - like CA15/I-15 or whatever. It's not a duplication. But with you that it's a silly idea.

[agentsteel53]

I-41/US41 is the same route - like CA15/I-15 or whatever. It's not a duplication. But with you that it's a silly idea.

74/74 will at one point have a signed split - one 74 going one way, one the other.  it may even be the case already.

[vdeane]

I think NY spaces it's 3di's so that if they were to add some they would still fit the consecutive system.  I-87 and I-81 both seem to fit this.  I-84 is again the anomaly though, as I-684 would be I-884 in a strict application of this.

[kurumi]

Wasn't there something about an AM radio station involved in Ft. Worth's I-820?

That's a maybe, involving WBAP 820 AM. I haven't seen an authoritative source confirming it.

[A.J. Bertin]

Another example... why is I-474 in Illinois (around Peoria) not I-274?

[1995hoo]

With regards to the x81s, there is continuity across states and they increase from south to north. Virginia uses 381 and 581, skipping 181 because it already existed in Tennessee (until I-26 ate it). Likewise, New York is numbering its new spur 781 so as to continue the trend and not reuse any of the other numbers.

....

The I-x81 situation in Virginia also came about because of the proximity of I-381 to I-181–it's only about 22 miles between those two interchanges via essentially a straight shot on I-81 and so the desire to avoid duplication was quite understandable.

States try to avoid having 2 of the same 3DIs in consecutive states or within 100 miles of each other along the mainline of 2DI's.   CT chose I-395 over I-195 to avoid confusion with the I-195 in RI/MA. At one point, I-195 was to be extended to I-295 in Johnston, RI, which at its closest point is less than 30 miles from I-395 in Killingly, CT. Also, I-395 goes into MA up to the Mass Pike, so there'd be some real confusion with 2 195's in MA unless the I-290 designation were carried south to the CT line.  Examples of x95's from south to north

195: FL, VA, NJ (PA), RI/MA, ME
295: FL, NC, VA/MD, DE/NJ, NY, RI/MA
395: FL, VA/DC, CT/MA, ME

....

The only real exception here would be the 695's, but the DC one was a recent addition.

There's also an I-195 near Baltimore (connects I-95 to BWI Airport) and an I-395 in downtown Baltimore (minuscule stub route that more or less connects I-95 to the Inner Harbor/ballpark area). Of course the Virginia/DC I-395 was originally I-95.

I-295 does not enter both Virginia and Maryland–it's two separate routes. Virginia's is a partial beltway around Richmond and Petersburg; Maryland's enters DC and connects I-95/495 to DC's I-695. Without looking it up I'm pretty positive the latter route existed first.

I'm pretty sure (again without looking it up) that Maryland has used more x95s than any other state–the only one they don't have is an I-995.

[kkt]

Some states are picky about not using the same number twice regardless of classification, so they let piddly state highways on the other side of the state guide their 3di selection.  Once upon a time, Wisconsin was one of these states.  Then we got I-39.  Now we want I-41.  We correctly abandoned that silly idea.  Interstates should always trump US and state highway numberings.

It's not silly.  Duplicating route numbers creates confusion giving directions, reporting location when calling 911, discussing highways among officials and legislators, creating reports like statistics for every route in a state, etc., etc.

If an interstate needs a number, a state route may need its number changed, but if there's an available number for an interstate it's only common sense to use the number that would not require a number change.

[MVHighways]

Some states are picky about not using the same number twice regardless of classification, so they let piddly state highways on the other side of the state guide their 3di selection.  Once upon a time, Wisconsin was one of these states.  Then we got I-39.  Now we want I-41.  We correctly abandoned that silly idea.  Interstates should always trump US and state highway numberings.

It's not silly.  Duplicating route numbers creates confusion giving directions, reporting location when calling 911, discussing highways among officials and legislators, creating reports like statistics for every route in a state, etc., etc.

If an interstate needs a number, a state route may need its number changed, but if there's an available number for an interstate it's only common sense to use the number that would not require a number change.

It does make sense to change the number. When I-86 was proposed to go through southern MA they changed Route 86 in Salisbury--the northeasternmost town in the state-- to Route 286. Out of respect and to avoid confusion New Hampshire did the same on their Route 286--the same road as MA 286. Then they changed it to I-84.

[Beltway]

I-295 does not enter both Virginia and Maryland–it's two separate routes. Virginia's is a partial beltway around Richmond and Petersburg; Maryland's enters DC and connects I-95/495 to DC's I-695. Without looking it up I'm pretty positive the latter route existed first.

VA I-295 was authorized at the inception of the Interstate highway system in 1956.  The southern end would have been at I-95 near Chester.  The extension to south of Petersburg was authorized in 1977.

[corco]

If an interstate needs a number, a state route may need its number changed, but if there's an available number for an interstate it's only common sense to use the number that would not require a number change.

I'd say there's a balancing point- if an I-202 were ever, for some crazy reason commissioned in Washington, and that was the number that made the most sense, it probably would make sense to re-evaluate whether 202 was necessary to be the number of that freeway, since 202 is already a pretty major state highway and maybe I-402 is available. If an I-971 were ever commissioned, and that was the number that made the most sense for the freeway, it would make sense to change the number of SR 971, since I doubt many people care that 971 is numbered 971.

[Henry]

Seems to me that state DOT's leave out certain numbers for one of three reasons, or possibly all:

a. There's already a state route with the omitted 3di number; or
b. The numbers are being reserved for future use.
c. The DOT wants to avoid potential confusion with a similar-numbered 3di in another state

Which leads me to wonder: Had the original I-595 in MD (cancelled I-170) been completed as planned, what would they do with the currently-designated one? I'm suspecting I-995, and still keep it hidden.

Another interesting note is I-85 spurs, which seem to have been randomly numbered at will.

I-185: Spurs to Columbus, GA, and Greenville, SC
I-285: Loop around Atlanta, GA
I-385: Spur to Greenville, SC
I-485: Loop around Charlotte, NC
I-585: Spur to Spartanburg, SC
I-785: Greensboro, NC-Danville, VA
I-985: Spur to Gainesville, GA

Note that this does not include the I-285 spur into Winston-Salem, NC or I-685 in Montgomery, AL, both future routes. I'm suspecting that it'll only be a matter of time before we see an I-885 somewhere, but I wouldn't hold my breath.

[agentsteel53]

It does make sense to change the number. When I-86 was proposed to go through southern MA they changed Route 86 in Salisbury--the northeasternmost town in the state-- to Route 286. Out of respect and to avoid confusion New Hampshire did the same on their Route 286--the same road as MA 286. Then they changed it to I-84.

I believe MA-295, in the northwest corner of the state, was allowed to keep its number.

[Beltway]

Which leads me to wonder: Had the original I-595 in MD (cancelled I-170) been completed as planned, what would they do with the currently-designated one? I'm suspecting I-995, and still keep it hidden.

The US-50 John Hanson Highway's first Interstate designation was to have been I-68.

[kkt]

I'd say there's a balancing point- if an I-202 were ever, for some crazy reason commissioned in Washington, and that was the number that made the most sense, it probably would make sense to re-evaluate whether 202 was necessary to be the number of that freeway, since 202 is already a pretty major state highway and maybe I-402 is available. If an I-971 were ever commissioned, and that was the number that made the most sense for the freeway, it would make sense to change the number of SR 971, since I doubt many people care that 971 is numbered 971.

The planners shouldn't start with saying "We need I-202."  They should start with saying "We need a loop route off I-2."  Then they find the best number for it.  They'd go through 402, 602, 802, and if none of them worked they'd consider 102 to 902.  If all of them were taken, then it would be time to renumbering the existing WA-202.

[roadman]

It does make sense to change the number. When I-86 was proposed to go through southern MA they changed Route 86 in Salisbury--the northeasternmost town in the state-- to Route 286. Out of respect and to avoid confusion New Hampshire did the same on their Route 286--the same road as MA 286. Then they changed it to I-84.

I believe MA-295, in the northwest corner of the state, was allowed to keep its number.

That is correct.  Of course, MA 295 is only two miles long and has the sole purpose of connecting NY 295 to MA 41 in Richmond, MA.  Given this, as well as its physical distance from I-295 within MA/RI, and the fact it doesn't intersect with any interstates (like old MA 86/current MA 286), it's a logical exception to the "no routes with same number" rule.

[1995hoo]

Seems to me that state DOT's leave out certain numbers for one of three reasons, or possibly all:
....

c. The DOT wants to avoid potential confusion with a similar-numbered 3di in another state

....

This prompts me to think of the unusual situation in the District of Columbia, where DC-295 (the only road that bears a "territorial highway" number) was given that number specifically because it was the same as an already-existing Interstate–it connects I-295 on the southern end and MD-295 on the northern end, although when the DC route number was first posted I-295 continued across the Anacostia River to a stub end at Barney Circle (it's now been truncated to end where it becomes DC-295). The idea of providing continuity to motorists with the "295" number all the way through trumped the potential confusion.....and it's not just motorists who might confuse the numbers, as some local media reports as recently as last week mixed up the "DC" portion with the Interstate portion.

[kphoger]

Like IL-255, I guess.

[Alps]

Another example... why is I-474 in Illinois (around Peoria) not I-274?

My best guess on that has to do with routings around the Quad Cities.

[Beltway]

Like IL-255, I guess.

Like VA-381