Which states allow number duplication?

[MNHighwayMan]

Minnesota does in limited cases:
-Two MN 62s - the original MN 62 is a rural two-lane road. The more well-known MN 62 in the Twin Cities came to be in 1988 when MnDOT took control of Hennepin County's Crosstown Expressway, County Road 62.
-US 61 and MN 61 (MN 61 replaced part of a decommissioned section of US 61)
-US 169 and MN 169 (MN 169 is a state "extension" of MN 169, separated by a few miles of US 53)
-US 65 and MN 65 (same as 169, though in this case the two directly intersected in downtown Minneapolis before US 65 was eliminated north of Albert Lea)

And in the same vein as the last two, there are also the former instances of MN-212 and 218. The former later became an extension of MN-5 and 36 and the latter largely became part of MN-25.

On the other side of the coin, MN 35, MN 90, and MN 94 were all renumbered (each had their numbers increased by 100; MN 190 has been decommissioned while the other two live on). So I guess to follow the OP's criteria, maybe US/state duplicates are allowed but state/interstate ones are not.

I think it's because MnDOT sees the state numbers as extensions of the US Route numbers–IE they're intended to be seen as the same route, just with a different shield. This was decidedly not the case with old MN-35, 90, and 94, so they were renumbered.

Edit: Another example of that is old MN-63, which was renumbered as 73 when US-63 was extended into Minnesota in the mid-1930s.

[US 89]

Utah has a hard policy of no duplications, as route numbers are defined legislatively. Before 1977, when legislative descriptions were changed to match signed routes, there were several duplications. That included a SR-15 which intersected I-15 (now SR-9), and a SR-84 which ran parallel to (and even intersected) I-84 in the Ogden area.

[GaryV]

Michigan has
US-8 and M-8
US-10 and M-10
US-24 and M-24
US-45 and M-45
I-69 and M-69
I-75 and M-75
I-94 and M-94
I-96 and M-96

Michigan originally (in 1926) did not have duplicates, except as noted below.  Thus M-16, M-23 and a few others disappeared and were renumbered.

The exception was where a state route extended from the US route.  US-24/M-24 is the only example of that left (even though they no longer touch at their former terminii in Pontiac).  Others were 25 and 131; there may have been more but I'm going from memory.

M-10 was a replacement for when US-10 was truncated at Bay City.

M-45 was created when M-50 through Grand Rapids was decommissioned after the coming of the freeways.  I guess they thought M-45 and US-45 were far enough apart.

Seems like when the Interstates came in, they didn't care that there were duplicate numbers.  Those brand spankin' new freeways weren't going to be confused with a state highway.

M-8 is a relatively new numbering for a rather old freeway.  It used to not have a number.  And again, it's a long way from US-8 which most people have never driven on in Michigan.

[vdeane]

There are also a handful of cases where a state route is a non-Interstate extension of an Interstate:

- NY 390
- NY 481
- NY 495
- NY 590
- NY 690
- NY 890

NY 878?  Though it's an odd case, with I-878 not signed, not acknowledged by NYSDOT (outside of the Functional Class Viewer), and only existing eastbound.

NY 495 is also an interesting case, being former I-495 but not connected to I-495.  Unless you count that piece of the LIE, which is signed as I-495, and it not being an interstate is an odd technicality only partially acknowledged by NYSDOT (in the Functional Class Viewer and touring route book); no idea what led to that, but IMO the whole LIE should be an interstate or, failing that, at least have more logical endpoints for the parts that are and aren't.

[Hurricane Rex]

Oregon has:
I-82/OR 82
I-205/OR 205

LG-TP260

[bulldog1979]

Michigan has
US-8 and M-8
US-10 and M-10
US-24 and M-24
US-45 and M-45
I-69 and M-69
I-75 and M-75
I-94 and M-94
I-96 and M-96

And historically, Michigan had:
US 25 and M-25
US 27 and M-27
US 33 and M-33
US 112 and M-112
US 131 and M-131

Additionally, there was a proposal for an M-275 as a continuation of I-275, and the US 102 and M-102 were probably a near miss, just months apart between the former's decommissioning and the latter's commissioning.

[Flint1979]

Michigan has
US-8 and M-8
US-10 and M-10
US-24 and M-24
US-45 and M-45
I-69 and M-69
I-75 and M-75
I-94 and M-94
I-96 and M-96

Michigan originally (in 1926) did not have duplicates, except as noted below.  Thus M-16, M-23 and a few others disappeared and were renumbered.

The exception was where a state route extended from the US route.  US-24/M-24 is the only example of that left (even though they no longer touch at their former terminii in Pontiac).  Others were 25 and 131; there may have been more but I'm going from memory.

M-10 was a replacement for when US-10 was truncated at Bay City.

M-45 was created when M-50 through Grand Rapids was decommissioned after the coming of the freeways.  I guess they thought M-45 and US-45 were far enough apart.

Seems like when the Interstates came in, they didn't care that there were duplicate numbers.  Those brand spankin' new freeways weren't going to be confused with a state highway.

M-8 is a relatively new numbering for a rather old freeway.  It used to not have a number.  And again, it's a long way from US-8 which most people have never driven on in Michigan.

I've been told and I read up on it that US-24 and M-24 never met up as the same highway. I figured that with M-24's southern terminus and US-24's northern terminus being about 12 miles apart that they were at one time joined because I know that US-24 use to end at Square Lake and US-10 was the routing north of that point. M-25 and US-25 indeed did meet up in Port Austin.

I wouldn't suspect any confusion between M-45 and US-45 considering they are plenty far enough apart. I would think that M-24 and US-24 get confused by people not familiar with Oakland County roads.

M-75 isn't really that far from I-75 but it would take a lot to get those two highways confused.

M-8 came about when the Davison was transferred to the jurisdiction of MDOT in the 90's and then was rebuilt around 1996. Even though some think the Davison is useless as a freeway it still carries about 50,000 vehicles a day. I have actually driven on US-8, I took that way to the Twin Cities one time about 15 years ago you basically turn onto it in Norway and then you're in Wisconsin within a few minutes. I honestly don't understand why it doesn't just end at US-141 in Wisconsin, it already has it's two state limit since it's under 300 miles. It's not in Minnesota for very long either about 22 miles but is in Wisconsin for about 255 miles.

[ilpt4u]

Illinois allows it; it even provides the first (?) example of an Interstate and US highway sharing a number within the same state (24). There were a few state routes that changed numbers due to intersecting new Interstate highways with the same number, most notably IL 80 (now 84) and IL 88 (now 40).

Other Land of Lincoln examples: AFAIK none intersect (not counting the I/IL 255 Freeway) Generally, most are in opposite areas of the state. US 6 and IL 6 are not that far away - Distance from Peoria to I-80

I & IL 64
I & IL 70
I & IL 72
I & IL 155
US & IL 50
US & IL 34
US & IL 14
US & IL 40
US & IL 6
US & IL 54 (IL 54 being a segment of decommissioned US 54)
US & IL 150

[kurumi]

Connecticut did allow duplicate routes long ago, but only for "A" suffixed state and US routes. For example, multiple CT 10A's existed, and multiple US 1A's. They did not secretly overlap connecting routes; they were distinct.

[Scott5114]

Arkansas: Duplication allowed with no restrictions. Two state routes can have the same number; this is a common occurrence.

Same applies for Oklahoma, although duplicate state routes are not as commonplace as in Arkansas. Most duplicate routes were either once joined but the middle section decommissioned (often because of the introduction of a higher-level route in the corridor, but sometimes simply because a highway was not needed there) or are two entirely unrelated routes, with one numbered to match a highway in an adjoining state.

[formulanone]

Florida permits route duplication. Most of its Interstates and US Routes have a similarly-numbered state route, though usually well-distanced from each other. On a few occasions, they renumbered the nearby state route; FL 27 intersected US 27, so the former was split up to FL 997 and FL 9336, since they were completed at different times. A1A was proposed as SR 1 for the 1940s Renumbering, but with US 1 alongside of it, the theory is that it was renamed/renumbered to prevent confusion.

There's some exceptions: US 17 and SR 17, which intersect at one point. SR 10, which is mostly a secret number for US 90, intersects I-10 several times, but only has one segment in Jacksonville where it is listed solely as SR 10 (mostly east of I-10's terminus). US 23 and SR 23 are in the same county, though FL 23 is fairly new...not sure why they didn't use another number for the much-newer route.

FDOT suggests that County Roads should not duplicate nearby numbers, but I'm not sure if they've ever intervened in renumbering one, other than to "upgrade" it to state road status.

[Max Rockatansky]

Florida permits route duplication. Most of its Interstates and US Routes have a similarly-numbered state route, though usually well-distanced from each other. On a few occasions, they renumbered the nearby state route; FL 27 intersected US 27, so the former was split up to FL 997 and FL 9336, since they were completed at different times. A1A was proposed as SR 1 for the 1940s Renumbering, but with US 1 alongside of it, the theory is that it was renamed/renumbered to prevent confusion.

There's some exceptions: US 17 and SR 17, which intersect at one point. SR 10, which is mostly a secret number for US 90, intersects I-10 several times, but only has one segment in Jacksonville where it is listed solely as SR 10 (mostly east of I-10's terminus). US 23 and SR 23 are in the same county, though FL 23 is fairly new...not sure why they didn't use another number for the much-newer route.

FDOT suggests that County Roads should not duplicate nearby numbers, but I'm not sure if they've ever intervened in renumbering one, other than to "upgrade" it to state road status.

It seems that FDOT doesn't really intervene.  There are several examples of State and County Route duplicating like FL 589 being a couple miles east of Hernando County Route 589.

[ftballfan]

Florida permits route duplication. Most of its Interstates and US Routes have a similarly-numbered state route, though usually well-distanced from each other. On a few occasions, they renumbered the nearby state route; FL 27 intersected US 27, so the former was split up to FL 997 and FL 9336, since they were completed at different times. A1A was proposed as SR 1 for the 1940s Renumbering, but with US 1 alongside of it, the theory is that it was renamed/renumbered to prevent confusion.

There's some exceptions: US 17 and SR 17, which intersect at one point. SR 10, which is mostly a secret number for US 90, intersects I-10 several times, but only has one segment in Jacksonville where it is listed solely as SR 10 (mostly east of I-10's terminus). US 23 and SR 23 are in the same county, though FL 23 is fairly new...not sure why they didn't use another number for the much-newer route.

FDOT suggests that County Roads should not duplicate nearby numbers, but I'm not sure if they've ever intervened in renumbering one, other than to "upgrade" it to state road status.

It seems that FDOT doesn't really intervene.  There are several examples of State and County Route duplicating like FL 589 being a couple miles east of Hernando County Route 589.

Then you have the 435's in Orlando

[WillWeaverRVA]

Virginia does not typically allow duplication, although there are two three exceptions:

- VA 13 came into existence after US 13 was already around...in fact, there was already another VA 13 at the time (it was a state route extension of US 13, which did not yet exist on the mainland).

- VA 360 and US 360. VA 360 is an old alignment of US 360.

- US 33 and VA 33; VA 33 is a state route extension of US 33.

North Carolina does not typically allow duplication except in cases where a state route number is assigned to a future interstate corridor (NC 140/I-140, NC 295/I-295, etc).

Make it six:  I-381/VA 381; US 211/VA 211; US 311 and VA 311.  The CTB in theory was going to discuss renumbering VA 311 when US 311 came back but the issue just kinda went away.

Argh, I should've known better since I've been by all of those recently.

[hbelkins]

One reason that route number duplication can be a bad thing...

Saw a Facebook post yesterday from Tennessee DOT about a road closure on "Route 70N." I automatically assumed it was for US 70N. After I read the suggested detour routes, I realized that it was not for US 70N, but for TN 70 north of Rogersville.

[MNHighwayMan]

One reason that route number duplication can be a bad thing...

Saw a Facebook post yesterday from Tennessee DOT about a road closure on "Route 70N." I automatically assumed it was for US 70N. After I read the suggested detour routes, I realized that it was not for US 70N, but for TN 70 north of Rogersville.

That's not a problem with number duplication—that's a problem of using ambiguous terminology. "Route 70N" can mean either a route labeled "70N," or it can mean "Route 70, N" as in NB Route 70.

[Rothman]

One reason that route number duplication can be a bad thing...

Saw a Facebook post yesterday from Tennessee DOT about a road closure on "Route 70N." I automatically assumed it was for US 70N. After I read the suggested detour routes, I realized that it was not for US 70N, but for TN 70 north of Rogersville.

That's not a problem with number duplication–that's a problem of using ambiguous terminology. "Route 70N" can mean either a route labeled "70N," or it can mean "Route 70, N" as in NB Route 70.

Wouldn't have to worry about ambiguity if duplication was avoided.

[roadfro]

Nevada does not allow duplication of route numbers on the state highway system.

(There used to be duplication of internal numbers for roads in the "frontage road" network, where same numbers were used for different roads in different counties. These have since been changed to include the county abbreviations as part of the number. These numbers aren't signed at all, except on field mileposts.)

[Flint1979]

I sometimes wish Michigan wouldn't duplicate routes. M-75 is in the same part of the state that a stretch of I-75 runs through, M-75 is west of I-75 by less than 20 miles. M-75 is basically just a spur route off of US-131 pretty much serving just Boyne City so unless you are going to Boyne City M-75 is pretty much a useless highway anyway.

M-94 is in the Upper Peninsula a long ways from I-94.
M-96 isn't too far from I-96 as it runs between Kalamazoo and Marshall.
M-69 is in the Upper Peninsula like M-94 it's a long ways from I-69.

[jp the roadgeek]

Rhode Island: No duplication.

Actually, there is.  There's RI 1A in South County that has 5 separate pieces between Westerly and North Kingstown with silent concurrencies with US 1 in between, and there's US 1A through Warwick, Cranston, Providence, and Pawtucket (which becomes MA 1A at the border).

[Road Hog]

Arkansas: Duplication allowed with no restrictions. Two state routes can have the same number; this is a common occurrence.

Same applies for Oklahoma, although duplicate state routes are not as commonplace as in Arkansas. Most duplicate routes were either once joined but the middle section decommissioned (often because of the introduction of a higher-level route in the corridor, but sometimes simply because a highway was not needed there) or are two entirely unrelated routes, with one numbered to match a highway in an adjoining state.

Arkansas does, of course, have numerous disjointed highways with the same number.

But I think the intent of the OP was duplication of numbers across designations (state/US/interstate). Arkansas until recently did have a restriction on duplication (with exceptions for future interstates, i.e. AR 440/I-440), but finally relaxed it when I-49 came on the scene because of US 49 on the other side of the state.

[TEG24601]

Michigan has
US-8 and M-8
US-10 and M-10
US-24 and M-24
US-45 and M-45
I-69 and M-69
I-75 and M-75
I-94 and M-94
I-96 and M-96

Michigan originally (in 1926) did not have duplicates, except as noted below.  Thus M-16, M-23 and a few others disappeared and were renumbered.

The exception was where a state route extended from the US route.  US-24/M-24 is the only example of that left (even though they no longer touch at their former terminii in Pontiac).  Others were 25 and 131; there may have been more but I'm going from memory.

M-10 was a replacement for when US-10 was truncated at Bay City.

M-45 was created when M-50 through Grand Rapids was decommissioned after the coming of the freeways.  I guess they thought M-45 and US-45 were far enough apart.

Seems like when the Interstates came in, they didn't care that there were duplicate numbers.  Those brand spankin' new freeways weren't going to be confused with a state highway.

M-8 is a relatively new numbering for a rather old freeway.  It used to not have a number.  And again, it's a long way from US-8 which most people have never driven on in Michigan.

I've been told and I read up on it that US-24 and M-24 never met up as the same highway. I figured that with M-24's southern terminus and US-24's northern terminus being about 12 miles apart that they were at one time joined because I know that US-24 use to end at Square Lake and US-10 was the routing north of that point. M-25 and US-25 indeed did meet up in Port Austin.

I wouldn't suspect any confusion between M-45 and US-45 considering they are plenty far enough apart. I would think that M-24 and US-24 get confused by people not familiar with Oakland County roads.

M-75 isn't really that far from I-75 but it would take a lot to get those two highways confused.

M-8 came about when the Davison was transferred to the jurisdiction of MDOT in the 90's and then was rebuilt around 1996. Even though some think the Davison is useless as a freeway it still carries about 50,000 vehicles a day. I have actually driven on US-8, I took that way to the Twin Cities one time about 15 years ago you basically turn onto it in Norway and then you're in Wisconsin within a few minutes. I honestly don't understand why it doesn't just end at US-141 in Wisconsin, it already has it's two state limit since it's under 300 miles. It's not in Minnesota for very long either about 22 miles but is in Wisconsin for about 255 miles.

I don't see route duplication being and issue in Michigan, since all state routes are M-X, and are spoken as such.  It isn't common to confuse them with the other route numbers.  In other states, like Washington, duplication could be confusing, because some people just use the route number, say "the" then route number, say "highway" then the route number, and others state the route type and number.

[cjk374]

Louisiana has duplicate route numbers:

I-59 & LA 59: they are only 20 miles apart. At the LA 59 exit, there are trail blazers pointing straight ahead on I-12.

I-10 & LA 10

I-12 & LA 12

I-20 & LA 20

I-55 & LA 55

I-49 & LA 49 (a 200+ mile interstate vs a 3.93 mile state highway.)

I-510 & LA 510

I-910 & LA 910

[Flint1979]

Michigan has
US-8 and M-8
US-10 and M-10
US-24 and M-24
US-45 and M-45
I-69 and M-69
I-75 and M-75
I-94 and M-94
I-96 and M-96

Michigan originally (in 1926) did not have duplicates, except as noted below.  Thus M-16, M-23 and a few others disappeared and were renumbered.

The exception was where a state route extended from the US route.  US-24/M-24 is the only example of that left (even though they no longer touch at their former terminii in Pontiac).  Others were 25 and 131; there may have been more but I'm going from memory.

M-10 was a replacement for when US-10 was truncated at Bay City.

M-45 was created when M-50 through Grand Rapids was decommissioned after the coming of the freeways.  I guess they thought M-45 and US-45 were far enough apart.

Seems like when the Interstates came in, they didn't care that there were duplicate numbers.  Those brand spankin' new freeways weren't going to be confused with a state highway.

M-8 is a relatively new numbering for a rather old freeway.  It used to not have a number.  And again, it's a long way from US-8 which most people have never driven on in Michigan.

I've been told and I read up on it that US-24 and M-24 never met up as the same highway. I figured that with M-24's southern terminus and US-24's northern terminus being about 12 miles apart that they were at one time joined because I know that US-24 use to end at Square Lake and US-10 was the routing north of that point. M-25 and US-25 indeed did meet up in Port Austin.

I wouldn't suspect any confusion between M-45 and US-45 considering they are plenty far enough apart. I would think that M-24 and US-24 get confused by people not familiar with Oakland County roads.

M-75 isn't really that far from I-75 but it would take a lot to get those two highways confused.

M-8 came about when the Davison was transferred to the jurisdiction of MDOT in the 90's and then was rebuilt around 1996. Even though some think the Davison is useless as a freeway it still carries about 50,000 vehicles a day. I have actually driven on US-8, I took that way to the Twin Cities one time about 15 years ago you basically turn onto it in Norway and then you're in Wisconsin within a few minutes. I honestly don't understand why it doesn't just end at US-141 in Wisconsin, it already has it's two state limit since it's under 300 miles. It's not in Minnesota for very long either about 22 miles but is in Wisconsin for about 255 miles.

I don't see route duplication being and issue in Michigan, since all state routes are M-X, and are spoken as such.  It isn't common to confuse them with the other route numbers.  In other states, like Washington, duplication could be confusing, because some people just use the route number, say "the" then route number, say "highway" then the route number, and others state the route type and number.

You don't have everyone saying the "M" and I'm one that doesn't always use it either. Like for M-47 I'll just call it 47 or Midland Road, same for 46 or Gratiot or Holland/Remington, but M-58 really never gets called by it's route number it's known by State Street and also Davenport Avenue in the one way stretch. It might just be a Saginaw County thing because M-46 is known as M-46 more popularly than it's road name in other parts of the state. And it's funny because for Bay Road I'll call it M-84 in Bay County but call it Bay Road in Saginaw County. In Bay County it's name is Westside Saginaw Road, then Salzburg, then Lafayette, then Garfield, then Washington. While M-84 is on the Salzburg/Lafayette stretch it has a wrong way multiplex with M-13.

[US71]

Arkansas has lots of state highway duplication.  AR 45 and AR 74 are two of the biggest offenders, but these were chopped up over the years.

But we also have US 59 and AR 59
US 49 and I-49 (200 mile separation)
AR 440 and I-440 (AR 440 likely to be upgraded sometime in the future)
AR 530 and I-530 (AR 530 a possible future reroute of I-530)