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Author Topic: Duplicate Interstate numbers?  (Read 22485 times)

Dustin DeWinn

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Duplicate Interstate numbers?
« on: January 09, 2017, 02:37:12 PM »

I know this is an amateur question, but I noticed there are duplicate Interstate designations. 495 is in Long Island as well as North Carolina, and possibly elsewhere.

I'm aware of some other duplicated interstates. I was wondering why this is? Surely there are plenty of numbers to use. Long Island's 495 doesn't connect with North Carolina's.

Thank you
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Big John

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Re: Duplicate Interstate numbers?
« Reply #1 on: January 09, 2017, 02:48:59 PM »

There are 4 duplicate 2-digit interstates (2di), 76, 84, 86, 88.  These are for shortage of numbers and they will never connect.  A case can be said for I-74 but it is technically planned to connect.

For 3di's, there are many duplicates as these are loop or spur routes off its parent.  Only rule is there can't be a duplicate in a single state.
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Re: Duplicate Interstate numbers?
« Reply #2 on: January 09, 2017, 02:53:56 PM »

If 3-digit Interstates (often abbreviated to 3di(s) on this forum) had to be unique across the whole country, then I-95 could only have 9 child routes. There are many more, so some have to be duplicated.

Sometimes they are duplicated even when it isn't necessary: there are two Interstates numbered I-291, even though no problem would result from one of them being renumbered I-491. This usually is not considered a problem.
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SidS1045

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Re: Duplicate Interstate numbers?
« Reply #3 on: January 09, 2017, 02:56:30 PM »

Three-digit Interstates are either spurs or loops of one- or two-digit Interstates, so they can be duplicated in different states.  There is no duplication of the one- or two-digit Interstates.  This was part of the original design of the Interstate system, where the mainline (one- or two-digit) Interstates would bypass cities and the loops or spurs would serve the cities and/or their suburbs.  (Not the way it worked out in every case, however.)  In general, spurs have an odd-numbered first digit and loops an even-numbered first digit.

Three-digit Interstates are also an exception to the usual rule about signing an Interstate's direction.  One- or two-digit Interstates are signed as east-west for even numbers and north-south for odd numbers.  Three-digit Interstates are labeled without regard to that scheme.
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hbelkins

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Re: Duplicate Interstate numbers?
« Reply #4 on: January 09, 2017, 03:06:29 PM »

Is there a rule against four-digit interstates?
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PHLBOS

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Re: Duplicate Interstate numbers?
« Reply #5 on: January 09, 2017, 03:11:03 PM »

Is there a rule against four-digit interstates?
Not for Hawaii.  :sombrero:

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epzik8

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Re: Duplicate Interstate numbers?
« Reply #6 on: January 09, 2017, 03:41:45 PM »

Is there a rule against four-digit interstates?
Not for Hawaii.  :sombrero:


Props to Hawaii for having Clearview signs.
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bing101

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Re: Duplicate Interstate numbers?
« Reply #7 on: January 09, 2017, 03:52:17 PM »

I know this is an amateur question, but I noticed there are duplicate Interstate designations. 495 is in Long Island as well as North Carolina, and possibly elsewhere.

I'm aware of some other duplicated interstates. I was wondering why this is? Surely there are plenty of numbers to use. Long Island's 495 doesn't connect with North Carolina's.

Thank you

Also there's I-495 in Washington D.C.

I-405 is in Washington, California and Oregon.
But California's I-405 is famous nationwide though.
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hbelkins

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Re: Duplicate Interstate numbers?
« Reply #8 on: January 09, 2017, 04:01:50 PM »

Please, let's not start listing all the duplicate 3di's.
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formulanone

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Re: Duplicate Interstate numbers?
« Reply #9 on: January 09, 2017, 04:09:30 PM »

Please, let's not start listing all the duplicate 3di's.

The uniquely-numbered 3dis might be a shorter list.
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Dustin DeWinn

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Re: Duplicate Interstate numbers?
« Reply #10 on: January 09, 2017, 05:01:56 PM »

Thank you all for the thorough replies.

Is there some standard to numbering conventions that is determinant on direction (North/South) or some other metric that makes making each interstate uniquely numbered.

 
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Re: Duplicate Interstate numbers?
« Reply #11 on: January 09, 2017, 05:07:27 PM »

Thank you all for the thorough replies.

Is there some standard to numbering conventions that is determinant on direction (North/South) or some other metric that makes making each interstate uniquely numbered.

Odd numbers from 5-99 (there is no 1 or 3) are north-south and increase going east.
Even numbers from 2-96 (there is no 98) are east-west and increase going north.
3-digit Interstates can have any posted direction. Those with an odd first digit are spurs, and those with an even first digit are loops.
3-digit Interstates that connect two different Interstates can be given either even or odd first digits.
Multiples of 5 are generally more important than others.
Generally, if an Interstate is 100 miles or more, it will have 2 digits, while those below 100 miles will have 3 digits.

There are several Interstates that break these rules, some more blatant than others.

Examples: Massachusetts has 84, 90, 91, 93, 95, 190, 290, 291, 391, 195, 295, 395, and 495.

I-84 is east-west and south of 90.
I-90 is also east-west, and since it is a multiple 5, it is "major", so it goes all the way to Seattle from Boston.
I-91, I-93, and I-95 are north-south. For the most part (I-93 and I-95 cross), numbers increase going east. I-95 goes from Maine to Florida, while 91 and 93 are nowhere near as long.
I-190 (odd first digit) has I-290 at one end without another Interstate at another end. This could be considered a minor violation for not connecting directly to I-90.
I-290 (even first digit) connects I-90 to I-495, being numbered off of I-90.
I-291 connects I-90 to I-91.
I-391 starts at I-91 and ends at a surface road.
I-195 goes from I-95 in Providence RI to near Cape Cod.
I-295 is a half-beltway of Providence RI.
I-395 connects I-95 in New London to I-90 near Worcester.
I-495 is a half-beltway of Boston MA. It is over 100 miles, but it would make no sense having 2 digits as it is clearly a half-beltway.
« Last Edit: January 09, 2017, 05:16:31 PM by 1 »
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Clinched, minus I-93 (I'm missing a few miles and my file is incorrect)

Traveled, plus US 13, 44, and 50, and several state routes

I will be in Burlington VT for the eclipse.

coatimundi

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Re: Duplicate Interstate numbers?
« Reply #12 on: January 09, 2017, 05:19:07 PM »

You could argue that 69 is disconnected, since it's now signed in a number of states. Though there is a plan to connect it, I would argue that connecting the segments is about as likely as connecting the two I-76 segments.
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Quillz

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Re: Duplicate Interstate numbers?
« Reply #13 on: January 09, 2017, 05:42:02 PM »

Is there a rule against four-digit interstates?
I don't know if such a scenario has ever been defined legally. I would imagine that on paper, it wouldn't be against the rules, but I would also imagine it would be recommended that such a scenario be avoided.

That said, I could see an interstate-quality loop or spur of a 3di being assigned a 4-digit number (i.e. something like I-2405 could be a loop for I-405, etc.)
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Quillz

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Re: Duplicate Interstate numbers?
« Reply #14 on: January 09, 2017, 05:43:48 PM »

Thank you all for the thorough replies.

Is there some standard to numbering conventions that is determinant on direction (North/South) or some other metric that makes making each interstate uniquely numbered.

 
Numbers increase west to east and south to north. That said, violations exist. I-99 is between I-79 and I-81, the majority of I-69 and I-71 exist west of lower odd numbers, and there is an I-238 even though there is no I-38.
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formulanone

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Re: Duplicate Interstate numbers?
« Reply #15 on: January 09, 2017, 07:11:22 PM »

Thank you all for the thorough replies.

Is there some standard to numbering conventions that is determinant on direction (North/South) or some other metric that makes making each interstate uniquely numbered.

As for 3-digit interstates, other than the even/odd first digits, the order in which they are assigned is not an exact science. Usually (but not always) the first interstate spur within a state is given the 1xx designation, and the first interstate loop is 2xx, et cetera.

Some states avoid intrastate route number duplication, and suggest another unused number. Sometimes, states try to apply it in some sort of north-south or east-west order, so that future numbers can be "reserved", but that seems to be rare.
« Last Edit: January 11, 2017, 09:05:44 PM by formulanone »
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jwolfer

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Re: Duplicate Interstate numbers?
« Reply #16 on: January 09, 2017, 11:41:07 PM »

Is there a rule against four-digit interstates?
Not for Hawaii.  :sombrero:


I think it should be 2H1 not H201

LGMS428

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NE2

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Re: Duplicate Interstate numbers?
« Reply #17 on: January 09, 2017, 11:57:50 PM »

H isn't a digit anyway.
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thenetwork

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Re: Duplicate Interstate numbers?
« Reply #18 on: January 10, 2017, 01:11:01 AM »

Is there a rule against four-digit interstates?
Not for Hawaii.  :sombrero:


I think it should be 2H1 not H201

LGMS428



The I-H201 shields and the Clearview font makes those signs look so video game-ish.   If someone showed you a photo of those signs at the turn of the century (2000), nobody would believe that those were real since neither the route nor font was in place yet.

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michravera

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Re: Duplicate Interstate numbers?
« Reply #19 on: January 10, 2017, 02:50:12 AM »

If 3-digit Interstates (often abbreviated to 3di(s) on this forum) had to be unique across the whole country, then I-95 could only have 9 child routes. There are many more, so some have to be duplicated.

Sometimes they are duplicated even when it isn't necessary: there are two Interstates numbered I-291, even though no problem would result from one of them being renumbered I-491. This usually is not considered a problem.

California currenlty uses 7 out of the 9 possible I-x80s. At times it had an eighth, and, in fact, would have used the ninth (and would probably use two more, if CASR-262 and CASR-237 were constructed as freeways between I-680 and I-880. I-238 was approved as what would (some say should) have been the ninth x80. CASR-180 prevented using it as an I- designation. I-480 was in use at the time. I-238 would be an I-x80, if one were available at the time of its naming.

California also uses 8 out of the 9 I-x05. There is currently no I-705 in California and I-305 exists but isn't signed.
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PHLBOS

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Re: Duplicate Interstate numbers?
« Reply #20 on: January 10, 2017, 09:24:11 AM »

Generally, if an Interstate is 100 miles or more, it will have 2 digits, while those below 100 miles will have 3 digits.

There are several Interstates that break these rules, some more blatant than others.

I-495 is a half-beltway of Boston MA. It is over 100 miles, but it would make no sense having 2 digits as it is clearly a half-beltway.
Let's not forget about I-83, the western I-86, I-97 (all three are less than 100 miles total) and I-476 (longer than 100 miles).  There's probably some others out there as well.

H isn't a digit anyway.
While technically correct (the routes P and the OO in your avatar aren't digits either), it's certainly being used/treated as such.

Similar could be said for letter-suffixed routes (1A, 1B, etc.) as well.
« Last Edit: January 11, 2017, 12:40:34 PM by PHLBOS »
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SP Cook

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Re: Duplicate Interstate numbers?
« Reply #21 on: January 10, 2017, 09:50:30 AM »

Theoretical 4di.  I would prefer the use of 4di in the place of a US route and I of the same number meeting, as happens with 74.  In fact what NC is doing to interstate numbering generally, with a 74 that will never connect to the "real" one, the use of the green shield in a different way than other states (to sign older version of the routes), the pointless zig-zag of 73 and 74, and the meeting of US and I of the same number is very confusing to the non-roadgeek.    In fact, as growth causes new interstates to have to be built, a 4di could be a better solution than all of these rule violations.  The 1 2 and 3 dis could sign the "orignal" system, which is esentually complete, and 4dis could be used for new constuction.

Hawaii.  I never understood why Hawaii used the H.  Yes, I get that federal bureaucrats use it and even the even more roadgeeky A and PR designations for roads that really don't even exist.  That is just bookkeeping.   But what information is imparted to the motorist by H2 being signed H2 rather than just 2?  You would have to be pretty stupid to not know you were in Hawaii, after all. 
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Re: Duplicate Interstate numbers?
« Reply #22 on: January 10, 2017, 10:25:44 AM »

If 3-digit Interstates (often abbreviated to 3di(s) on this forum) had to be unique across the whole country, then I-95 could only have 9 child routes. There are many more, so some have to be duplicated.

Sometimes they are duplicated even when it isn't necessary: there are two Interstates numbered I-291, even though no problem would result from one of them being renumbered I-491. This usually is not considered a problem.

California currenlty uses 7 out of the 9 possible I-x80s. At times it had an eighth, and, in fact, would have used the ninth (and would probably use two more, if CASR-262 and CASR-237 were constructed as freeways between I-680 and I-880. I-238 was approved as what would (some say should) have been the ninth x80. CASR-180 prevented using it as an I- designation. I-480 was in use at the time. I-238 would be an I-x80, if one were available at the time of its naming.

California also uses 8 out of the 9 I-x05. There is currently no I-705 in California and I-305 exists but isn't signed.

New York has used up all the I-x90s on its own.  My solution has been to get rid of I-790 in Utica if a real additional one is needed.
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Henry

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Re: Duplicate Interstate numbers?
« Reply #23 on: January 10, 2017, 10:41:55 AM »

Also, the new I-87 in NC could theoretically connect to the NY original, but no such plan exists right now.
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Re: Duplicate Interstate numbers?
« Reply #24 on: January 10, 2017, 11:13:53 AM »

If 3-digit Interstates (often abbreviated to 3di(s) on this forum) had to be unique across the whole country, then I-95 could only have 9 child routes. There are many more, so some have to be duplicated.

Sometimes they are duplicated even when it isn't necessary: there are two Interstates numbered I-291, even though no problem would result from one of them being renumbered I-491. This usually is not considered a problem.

California currenlty uses 7 out of the 9 possible I-x80s. At times it had an eighth, and, in fact, would have used the ninth (and would probably use two more, if CASR-262 and CASR-237 were constructed as freeways between I-680 and I-880. I-238 was approved as what would (some say should) have been the ninth x80. CASR-180 prevented using it as an I- designation. I-480 was in use at the time. I-238 would be an I-x80, if one were available at the time of its naming.

California also uses 8 out of the 9 I-x05. There is currently no I-705 in California and I-305 exists but isn't signed.

New York has used up all the I-x90s on its own.  My solution has been to get rid of I-790 in Utica if a real additional one is needed.
Now we just need a problem to apply that solution. I don't really see any other I-x90 candidate locations. Even Berkshire spoor can become I-x87.. Although I-1190 would be cool.
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