Longest highways without a single concurrency

[JayhawkCO]

For US highways it's US-24.

I'm assuming you just mean within Michigan, right? Nationally, I know that right near where I live, US 24 is concurrent with US 40 between Lawrence, KS, and KC.

Off the top of my head, I also recall some overlaps with US 285 & I-25 when I was out in Colorado almost a year ago.

It has tons of concurrencies in CO.  US285, CO67, I-25, CO21, US40, US287, I-70, and US385.

[Dirt Roads]

North Carolina:  probably NC-12 along the Outer Banks.  It's 148 miles, including both of the ferry routes.  In addition to not having any concurrencies, it only connects with US-70 in Sea Level.  The junction with NC-45 is virtual (since NC-12 sits alongside the ferry dock for NC-45 at Ocracoke).  Then at the two interconnections on the Outer Banks (first with the terminii of US-64 and US-158 at Whalebone Junction, and the other one with US-158 at Duck) neither one actually intersects with NC-12.

[SkyPesos]

Interstate: I-270 at 34 miles*

Along with I-270 in OH I mentioned above, I-270 is also the longest interstate without a concurrency in Missouri. So that's 3 of the 4 270 variants!

[US 89]

For Utah:

Interstates - all 2dis overlap at least one other interstate or US route somewhere in the state, leaving I-215 as winner by default
15: 50, 6, 89, 80, 84, (30)
70: 89, 50, 191, 6
80: 15, 189
84: (30), 15
215: none - 28.9 miles

US Highways - all but two definitely have a concurrency, and another one maybe does depending on whose documentation you look at. If you trust AASHTO and signs, the winner is US 163 at 41.4 miles in the state. If you trust UDOT, it's US 491 at 17 miles.
6: 50, 15, 89, 191, 70, 50
40: 189, 191
50: 6, 15, 89, 70, 191, 6
89: 70, 50, 6, 15, 91
91: 89
163: (191) - 41.4 miles
189: 40, 80
191: (163), 70, 50, 6, 40
491: none - 17.0 miles

US 163 ends at US 191 southwest of Bluff according to both AASHTO (since 2008) and signage on the ground (since 2004), but UDOT documentation maintains a concurrency with 191 all the way up to I-70 at Crescent Jct.

State Routes - SR concurrencies are quite rare in this state. SR 30 is the longest route in the state, but only when you include a couple of unsigned concurrencies with interstates and US highways (in Utah, state routes do not increase mileage along concurrencies where they are not the primary route). So that means Utah's winner is SR 24 at 160.3 miles.

[FrCorySticha]

Montana:
Interstates - If business loops don't count as a concurrency, I-115 in Butte is 1.9 miles. If you count concurrent business loops, all Interstates in MT have concurrencies.
US - All US Highways have concurrencies.
State - Again not counting business loops, MT 59 is 195 miles. Otherwise MT 24 holds the title with 134 miles.

North Dakota:
Interstates - I-194 in Bismarck is 1.1 miles.
US - Not counting business loops, US 10 is 8 miles. Otherwise, all US Highways have concurrencies.
State - ND 14 is 175 miles according to Wiki.

[jlam]

Arizona
Interstate - I-8 at 173.33 miles (only interstate in AZ that qualifies)
US Highway - US 89A at 86.90 miles
State Highway - SH86 at 118.12 miles

[Flint1979]

For US highways it's US-24.

I'm assuming you just mean within Michigan, right? Nationally, I know that right near where I live, US 24 is concurrent with US 40 between Lawrence, KS, and KC.

Yep no concurrencies along it in Michigan.

[mukade]

For Indiana:

Overall it's I-64 at 123 miles

Ahem...

2021 Western road trip Day 14 - 103 by H.B. Elkins, on Flickr

Well, there is always I-275 at 3.16 miles.

[CardInLex]

For Indiana:

Overall it's I-64 at 123 miles
For US highways, all of them except for the 0.64 miles of US 131 have concurrencies.
For state highways, the longest I can find is the northern segment of IN 63 at 63 miles.

I-64 has concurrency with IN 62 beginning at MM 118 and then US 150 beginning at MM 119

[paulthemapguy]

Illinois highways have concurrencies so frequently that I think the answer for Illinois state routes is IL-125, at only 37 miles. IL-25 isn't far behind at 35 miles. The concurrency-free highway with the most mileage in Illinois looks like Interstate 24, oddly, at 39 miles. Every other 2di in Illinois has a concurrency somewhere in the state. Every US highway in Illinois has a concurrency somewhere in the state.

[bob7374]

Massachusetts I believe would be I-90. MA 28 and US 20 are the only things longer and they have concurrencies with tons of things.

New Hampshire (and I had to look this up to confirm) is NH 175, just over 25 miles by itself. NH 110 is just behind it a half mile shorter.

For Mass., i-90 East has an unsigned concurrency with MA 1A from I-93 to its end in East Boston, but the first 133 miles are concurrency free. Then there's about 52 miles of I-95, excluding the 128 concurrency.

[NWI_Irish96]

For Indiana:

Overall it's I-64 at 123 miles
For US highways, all of them except for the 0.64 miles of US 131 have concurrencies.
For state highways, the longest I can find is the northern segment of IN 63 at 63 miles.

I-64 has concurrency with IN 62 beginning at MM 118 and then US 150 beginning at MM 119

Forgot about those, was just thinking about concurrencies with other interstates. No interstates in Indiana without concurrencies then.

[roadman65]

Florida would count for I-10 and I-4, but you have those unsigned state numbers like SR 8 and SR 400.  For I-95 now you have both US 1 and US 17, but if I-75 wasn't SR 93 it would be the winner in the state.

[SkyPesos]

Forgot about those, was just thinking about concurrencies with other interstates. No interstates in Indiana without concurrencies then.

I-275?

[LilianaUwU]

Florida would count for I-10 and I-4, but you have those unsigned state numbers like SR 8 and SR 400.

I wouldn't count unsigned state highway counterparts as concurrencies, honestly.

For Québec highways, QC-167 is probably the winner, though QC-389 might also be up there.

[Occidental Tourist]

Fairly certain it's CA 96 for California at 147 miles.

Wouldn't Interstate 8 qualify at 178 miles?

[SkyPesos]

Would I-8 be the longest interstate overall without concurrencies? I don't see any green highlighted boxes when skimming its Wikipedia page.

[zachary_amaryllis]

Colorado
Interstate: I-225 - 12 Miles (the only one)
U.S. Highway: US350 - 72 miles
State Highway: CO149 - 118 miles

Wyoming
Interstate: None
U.S. Highway: None
State Highway: WYO28 - 96 miles

co 14 has to come in second for state highways, 92 miles from walden (where it runs with 125 for a minute) to teds place (where it either pauses, or runs with 287)

[mukade]

Forgot about those, was just thinking about concurrencies with other interstates. No interstates in Indiana without concurrencies then.

I-275?

Correct. As mentioned above.

Even US 131 is (or at least used to be) also considered SR 13, although it is not signed that way.

[JayhawkCO]

Colorado
Interstate: I-225 - 12 Miles (the only one)
U.S. Highway: US350 - 72 miles
State Highway: CO149 - 118 miles

Wyoming
Interstate: None
U.S. Highway: None
State Highway: WYO28 - 96 miles

co 14 has to come in second for state highways, 92 miles from walden (where it runs with 125 for a minute) to teds place (where it either pauses, or runs with 287)

I don't think the OP intended longest stretch without a concurrency, just a route that didn't have any.

[jp the roadgeek]

Massachusetts I believe would be I-90. MA 28 and US 20 are the only things longer and they have concurrencies with tons of things.

New Hampshire (and I had to look this up to confirm) is NH 175, just over 25 miles by itself. NH 110 is just behind it a half mile shorter.

For Mass., i-90 East has an unsigned concurrency with MA 1A from I-93 to its end in East Boston, but the first 133 miles are concurrency free. Then there's about 52 miles of I-95, excluding the 128 concurrency.

I thought MA 1A went through the Callahan/Sumner tunnels and would stay on 93/1/3 as a silent concurrency with its parent up to the junction. Otherwise, 495 would be the longest in MA.

[roadman65]

If the OP meant single routes end to end no matter what states, GA is definitely out, unless you count the small SPUR designations or small three digit rural highways.

[thspfc]

I-794 is the only Interstate in WI that qualifies (3.5 miles).
All of the US routes have a concurrency at one point.
The longest state route without a concurrency could very well be WI-153 (61 miles).

[ahj2000]

In VA, the longest "solo"  interstate is 295, 52.75 around the east and north sides of Richmond.
Longest US route here is a pickle–but it looks like (as fair as mainline route go) it's 219, with a whopping 1.3 miles.
Finally, for state routes, VA 28 takes the cake, at 49 miles, from a rural 2 laner from Remington, up to Manassas and then a massive 6/8 lane freeway through suburban/exurban areas in Fairfax and Loudon counties, passing Dulles airport. It's an interesting drive for sure to get the radical change in the route as you drive it.

[jeffandnicole]

For New Jersey...

I believe the GSP wins in NJ, at 88 miles (around MP 84 to MP 172 at the NY State border).

If you wanna get technical with the wording "longest highway", the NJ Turnpike, as a highway, doesn't have a concurrency for 117 or so continuous miles, with its sole concurrency being from MP 0 to MP 0.9 with US 40.  The remainder of the highway has two different route numbers, but they never overlap.