Shortest duplex?

[Dr Frankenstein]

Hwys 108 and 271, Saint-Éphrem-de-Beauce, QC: 81 metres.
Hwys 133 and 227, Saint-Sébastien, QC: 28 metres.

[StogieGuy7]

Honorary mention must go out to the I-5/I-10 duplex in downtown Los Angeles, which is less than one mile in length but which carries more traffic than any other duplex in the USA. 

[NE2]

Honorary mention must go out to the I-5/I-10 duplex in downtown Los Angeles, which is less than one mile in length but which carries more traffic than any other duplex in the USA. 

It looks like I-75/I-85 and I-405/SR 22 carry more.

[Alps]

How about CR 524, 526, 539 in Allentown, NJ?


Now wait, what is this Alps Bistro business?

[formulanone]

Wonder if FL80 and FL29 are technically duplexed for what appears to be one block; SR29 intersects 80 in LaBelle, then shifts one block to continue north or south. It's probably 300 feet or so, but not signed.

[Darkchylde]

Not sure of the exact distance, but the duplex of LA 25 and LA 40 in Folsom is extremely short, about a block or two.

[mcdonaat]

LA 1203 and US 71 between Tioga and Pineville, LA. Unsigned, but LA 1203 does follow US 71 for about 50 feet or so.

[apeman33]

K-7 and K-31 in Bourbon County are concurrent for less than a full mile. But I don't know the actual distance. I can't think of any shorter in Kansas now. There were two that I remember that were a block or less before the routes were changed: U.S. 54/U.S. 169/K-57 in Iola were together for one block and if U.S. 154/K-154 officially ended at U.S. 50 rather than U.S. 56/283, then it's concurrency with 56/283 was less than a full block.

[roadfro]

Nevada does not allow state highways to overlap any other routes, so the only overlaps that exist are U.S. Routes onto other U.S. routes or or Interstate highways.

The shortest of these overlaps in Nevada is US 95's short overlap on US 50 in Fallon, NV. The US 95 alignment shifts over about 1/4 mile east using US 50 in the center of town.

Any other US highway overlapping with an US/Interstate highway in Nevada lasts a distance of several miles.

[vtk]

The shortest one I can think of is US 23 SB* with US 33 EB along Livingston Ave in Columbus, at about 400 feet.

The shortest one on a freeway I can think of is OH 16 EB and OH 37 EB near Granville, for about 850 feet.  (The westbound counterpart is 1000 feet longer.)

The shortest one I can think of that doesn't involve one-way halves of routes is OH 38 and OH 161 at Chuckery, (west of Plain City), at about 1000 feet.

[cjk374]

There's at least two shorter...per LaDOTD shapefiles, US 190/LA 434 in Lacombe is 1,697ft (0.32mi) and US 11/LA 433 in Slidell is 1,653ft (0.31mi).

If LA 151 indeed reaches to the south part of this intersection then it may be a winner...56 feet. 151 is signed as straight ahead on the southern zig zag of 1st street and Hazel st in Arcadia, LA. Cosigned with either US 80 or LA 9.

https://maps.google.com/maps?ll=32.54888,-92.920346&spn=0.001212,0.001754&t=m&z=19

Googlemaps is not quite correct.  US 80 WEST/LA 9 NORTH (1st St.) actually continues straight ahead and doesn't zig-zag.  The street represented a block up is US 80 WEST TRUCK ROUTE/LA 798-1 (2nd St.). So the multiplex is actually between LA 151 & US 80 TRUCK ROUTE.

On the west side of Ruston, LA, LA 818 multiplexes with US 80 for about 1/10th of a mile.

[TheStranger]

Shortest in California is in Redding - Route 44's concurrency with Route 273 between 44's western terminus at Route 299, and Tehama Street:

http://maps.google.com/maps?q=Redding&hl=en&ll=40.586956,-122.38821&spn=0.012922,0.017145&sll=37.269174,-119.306607&sspn=13.851002,17.556152&hnear=Redding,+Shasta,+California&t=m&z=16

Eastbound the concurrency is 4 blocks, westbound just 2.

[agentsteel53]

as far as I can tell, New Mexico has one state route multiplex: route 9 jogs along route 338 for one block in Animas.

http://goo.gl/maps/dTqoq

Google Maps gives no finer granularity than 0.1 mile, but it looks to be about 400 feet.

[NE2]

Shortest in California is in Redding - Route 44's concurrency with Route 273 between 44's western terminus at Route 299, and Tehama Street:

http://maps.google.com/maps?q=Redding&hl=en&ll=40.586956,-122.38821&spn=0.012922,0.017145&sll=37.269174,-119.306607&sspn=13.851002,17.556152&hnear=Redding,+Shasta,+California&t=m&z=16

Eastbound the concurrency is 4 blocks, westbound just 2.

Shorter than I-680/SR 84?

[TheStranger]

Shortest in California is in Redding - Route 44's concurrency with Route 273 between 44's western terminus at Route 299, and Tehama Street:

http://maps.google.com/maps?q=Redding&hl=en&ll=40.586956,-122.38821&spn=0.012922,0.017145&sll=37.269174,-119.306607&sspn=13.851002,17.556152&hnear=Redding,+Shasta,+California&t=m&z=16

Eastbound the concurrency is 4 blocks, westbound just 2.

Shorter than I-680/SR 84?

According to Google Maps, that one in Sunol (which only applies to eastbound 84 and northbound 680) is 0.3 mile...

while in comparison, the westbound 44/northbound 273 concurrency in Redding is 0.2 mile.  (Eastbound is longer, at 0.3 mile)

The 44/273 duplex only dates back to 2002 (when 299 was rerouted to use Lake Boulevard and 44 given the entire mainline of the east-west freeway into town), so based on Historicaerials shots, 84/680 was the shortest from about 1966 until then.

[ibagli]

The shortest one I can think of that doesn't involve one-way halves of routes is OH 38 and OH 161 at Chuckery, (west of Plain City), at about 1000 feet.

OH 16 and OH 310 are duplexed for around 600 feet in Pataskala.

[SteveG1988]

US 130 and US206 in NJ, no interaction other than both going through the same area. I think it is 1 mile at most. But it probably carries a ton of traffic as the two routes cross over each other.

[theline]

In South Bend, EB Business US 20 and SB SR 933 share a one-block concurrency on Main St., a one-way street. They have no concurrency in the other direction. How's that for an oddity?

[DandyDan]

In South Bend, EB Business US 20 and SB SR 933 share a one-block concurrency on Main St., a one-way street. They have no concurrency in the other direction. How's that for an oddity?

I'd have to think that is more common than you think because sometimes, a one-way pair begins at an intersection, which requires you to go over a block.  Anyway, the intersection is usually a major road through a city, which can often be a state highway.  I think the southern end of Illinois Route 70 overlaps with westbound Business Route 20 in Rockford, in a way similar to your example.  I thought I've seen another example of that somewhere but can't place it at the moment.

[agentsteel53]

what about any multiplexes arising from two perpendicular roads meeting in a roundabout?  by necessity, certain quadrants of the roundabout will carry both - in one direction only. 

[vtk]

what about any multiplexes arising from two perpendicular roads meeting in a roundabout?  by necessity, certain quadrants of the roundabout will carry both - in one direction only. 

That depends on how one interprets the roundabout geometry.  In most modern roundabouts where the radial roads form angles near 90 degrees, I interpret it like a closely spaced group of four yield-controlled intersections.  If two routes cross at such a roundabout, my interpretation says the routes cross, not overlap.  On the other hand, if you increase the angular size of one "quadrant" to more than about 120 degrees, the intersection in that quadrant is stretched out and becomes two, and there may be overlap of routes between them.  Adding a fifth road to the roundabout would ensure the existence of an overlap between two crossing routes.

[mjb2002]

US 78/SC 39 in Williston, S.C. duplexes for about 0.2 miles. From the Price Wise to the BP. That's it.

The duplex itself is not signed. All of the signage is on either terminus of the duplex.

[kphoger]

what about any multiplexes arising from two perpendicular roads meeting in a roundabout?  by necessity, certain quadrants of the roundabout will carry both - in one direction only. 

That depends on how one interprets the roundabout geometry.  In most modern roundabouts where the radial roads form angles near 90 degrees, I interpret it like a closely spaced group of four yield-controlled intersections.  If two routes cross at such a roundabout, my interpretation says the routes cross, not overlap.  On the other hand, if you increase the angular size of one "quadrant" to more than about 120 degrees, the intersection in that quadrant is stretched out and becomes two, and there may be overlap of routes between them.  Adding a fifth road to the roundabout would ensure the existence of an overlap between two crossing routes.

Roundabouts are typically considered "intersections", not a separate roadway.  So I would agree with the concept of the roads "crossing".  Put another way:  I wouldn't dream of posting a reassurance marker on the roundabout itself, so neither would I consider it to be a duplex.

[agentsteel53]

Roundabouts are typically considered "intersections", not a separate roadway.  So I would agree with the concept of the roads "crossing".  Put another way:  I wouldn't dream of posting a reassurance marker on the roundabout itself, so neither would I consider it to be a duplex.

generally, an overlap of fewer than N blocks does not get a reassurance, where N is for sure greater than 2, and probably as much as 6-7.

the large roundabout in Boise City, Oklahoma has been discussed elsewhere as having the most routes multiplexed.  none are multiplexed solely through the circle, though, as no route goes through east-west.  385 goes through north-south.

[kphoger]

I get it that duplex reassurances are not actually signed for distances that short, but I find it believable that one might exist somewhere.  However, I find the idea of a duplex being signed on an actual roundabout quite unbelievable.

The "roundabout" in Boise City is not a proper modern roundabout, and I would in fact not consider that to be one intersection.  I drove a very similar traffic circle in Benton (IL) almost daily for some time; it was an uncontrolled circle, with nobody having a yield sign to anybody else, and had very high traffic volume.  Nobody knew exactly what to do, whether to go or yield.  I started treating it as an arrangement of four T intersections, thereby giving the circulation right of way and an implied yield to all approaches.  To me, this makes more sense than counting it as one big intersection with a building in the middle.  So, in the case of Boise City, I would consider each bend in the "circle" to be a multiplex of approximately one block (half a block one direction, then a 90° bend and half a block in the next direction).