Longest interstate concurrences

[robbones]

I 20 & I 59 run concurrent from Meridian, MS to Birmingham, AL for roughly 170 miles. Are there any others that run longer?

[adventurernumber1]

Definitely. Idk for certain, but I could safely say the I-80/I-90 concurrency in Ohio & Indiana may be the longest.

[robbones]

The 80/90 concurrency is about twice as long as 20/59.

[pianocello]

As for longest concurrency involving an Interstate, I-25/US-87 takes the cake by a longshot. It's about 475 miles between Raton, NM, where 87 joins 25, and Glenrock, WY, where 87 leaves 25.

[roadman65]

As for longest concurrency involving an Interstate, I-25/US-87 takes the cake by a longshot. It's about 475 miles between Raton, NM, where 87 joins 25, and Glenrock, WY, where 87 leaves 25.

I think they leave in Fountain, CO and part ways for several miles to return via ramps that do not exist.

[NE2]

As for longest concurrency involving an Interstate, I-25/US-87 takes the cake by a longshot. It's about 475 miles between Raton, NM, where 87 joins 25, and Glenrock, WY, where 87 leaves 25.

I-25/US 85 is longer, if we're including overlaps that the states ignore.

[pianocello]

Oh, right. I forgot 85 made it all the way down to Texas.

[Zzonkmiles]

The 40/85 concurrency in NC is not the longest, but it is a blast to drive. Not much in the way of speed traps and traffic tends to flow very fast there. Very well designed, IMO. 

[Thing 342]

The 40/85 concurrency in NC is not the longest, but it is a blast to drive. Not much in the way of speed traps and traffic tends to flow very fast there. Very well designed, IMO. 

A literal blast as well. I was once tailgated going 85 on that road.

[NE2]

A literal blast as well.

Why, did something explode? Or is that not a literal literal?

[agentsteel53]

I was once tailgated going 85 on that road.

happens to me once every 3-400 miles on the freeway.  nothing to write home about.

tailgated at 100 is something else - especially when you move over to let them by, and they move over because tailgating is fun shit.

[Brandon]

I was once tailgated going 85 on that road.

happens to me once every 3-400 miles on the freeway.  nothing to write home about.

tailgated at 100 is something else - especially when you move over to let them by, and they move over because tailgating is fun shit.

I think they believe they're dogs who feel an extreme need to sniff up some one else's ass.  Big, two-ton dogs.

[SD Mapman]

As for longest concurrency involving an Interstate, I-25/US-87 takes the cake by a longshot. It's about 475 miles between Raton, NM, where 87 joins 25, and Glenrock, WY, where 87 leaves 25.

I-25/US 85 is longer, if we're including overlaps that the states ignore.

85 does leave the interstate in Fountain, so I don't know how that affects anything.

As for longest concurrency involving an Interstate, I-25/US-87 takes the cake by a longshot. It's about 475 miles between Raton, NM, where 87 joins 25, and Glenrock, WY, where 87 leaves 25.

I think they leave in Fountain, CO and part ways for several miles to return via ramps that do not exist.

See above sentence.

[NE2]

As for longest concurrency involving an Interstate, I-25/US-87 takes the cake by a longshot. It's about 475 miles between Raton, NM, where 87 joins 25, and Glenrock, WY, where 87 leaves 25.

I-25/US 85 is longer, if we're including overlaps that the states ignore.

85 does leave the interstate in Fountain, so I don't know how that affects anything.

It's simple enough to calculate - Las Cruces to Fountain is longer than Raton to either Fountain or anywhere else. This does assume that US 85 never leaves the Interstates in New Mexico - the AASHTO log is unclear, probably because it was written before I-25 was complete.

[Kacie Jane]

I'm confused.  Is your argument that US 85 leaves the interstate in Fountain but US 87 doesn't?  Even so, the US 85 concurrency would still be longer, since it follows I-25 all the way to its end in Las Cruces.  That's roughly 580 miles to Fountain, a full hundred more than pianocello's 475 figure for US 87.

ETA: Sorry, NE2 got here first, but yeah, what he said.

[pctech]

How are exit numbers handled on concurrent interstates?

[agentsteel53]

How are exit numbers handled on concurrent interstates?

there's always a route that's deemed "primary" whose exit numbers are used.  I think it is usually the lowest-numbered of the set.

[NE2]

How are exit numbers handled on concurrent interstates?

This is covered in the MUTCD: http://mutcd.fhwa.dot.gov/htm/2009/part2/part2e.htm#figure2E21
In short, either route can be used if both are Interstates. Usually it's the lower number or the one that was there first (e.g. I-40/85).

[Brandon]

How are exit numbers handled on concurrent interstates?

there's always a route that's deemed "primary" whose exit numbers are used.  I think it is usually the lowest-numbered of the set.

But not always, even if they were assigned at the same time.

I-90/94 in Illinois carries I-94's numbers even though both were assigned at the same time.  I suspect this was due to I-90 not being complete between Schaumburg and Elmhurst (current I-290 after 1978).

I-80/294 uses I-294's mileposts (and exit numbers when assigned) as the road is also the Tri-State Tollway.  I-74/280 uses I-74's mileposts.

Others:
I-55/72 and I-55/74 use I-55's mileposts and exit numbers (I-55 was the lower number).
I-57/64 and I-57/70 use I-57's mileposts and exit numbers (I-57 was the lower number).
I-55 and I-70 enter the state together (with I-64), yet I-70 continues I-270's mileposts and exit numbers after they separate (leading to a break in the space-time continuum of about 5 miles).
I-39/90 uses I-90's mileposts and exit numbers as I-90 was there first.
I-80/94 uses I-80's mileposts and exit numbers (I-80 was the lower number).
I-270 and I-280 continue their exit numbering from their previous states (Missouri and Iowa, respectively).

[NE2]

I-90/94 in Illinois carries I-94's numbers even though both were assigned at the same time.  I suspect this was due to I-90 not being complete between Schaumburg and Elmhurst (current I-290 after 1978).

The 1975-76 official is the first with exit numbers, but shows no exit numbers at all on I-90, even on the Dan Ryan, despite I-94 north of Ohio-Ontario and south of the Skyway having numbers. The 1977-78 official shows I-90 exit numbers on the Ike, but only west of IL 50. The 1979-80 and 1981-82 officials show no exit number changes (I-290 continues to use I-90's mileage and no numbers on the JFK west of I-94). The 1983-84 official finally has the modern exit numbers, and is the first to put them on the Ike east of IL 50 and the Dan Ryan north of the Skyway. So in a sense, I-94 was there first, since using I-90's mileage would have either meant changing the numbers on the JFK or jumping from 51 to 97? at the Circle.

[CNGL-Leudimin]

I-55 and I-70 enter the state together (with I-64), yet I-70 continues I-270's mileposts and exit numbers after they separate (leading to a break in the space-time continuum of about 5 miles).

This is no longer the case, I-70 now enters IL separate from I-55 (and I-64, with which bumps).

[Brandon]

I-55 and I-70 enter the state together (with I-64), yet I-70 continues I-270's mileposts and exit numbers after they separate (leading to a break in the space-time continuum of about 5 miles).

This is no longer the case, I-70 now enters IL separate from I-55 (and I-64, with which bumps).

Oops, my bad (I should've known better - taken it two different times since it opened).  It has about the same amount of mileage prior to meeting I-55, so the difference is negligible between the two.

[hbelkins]

I-75 has two concurrencies with lower-numbered interstates in Kentucky. In both cases, I-75's mileage and exit numbers are used.

[roadman65]

What about three digit numbers overlapped with two digits?  I have seen plenty that use the three digit route number exits such as around Knoxville, TN.  I-75 uses I-640's exit numbering.

Then, as mentioned before, I-83 uses I-695's numbers even though no exits during the overlap, it is at the split that I-83 leaves I-695 with an exit number and not I-695 leaving I-83.

[SSOWorld]

What about three digit numbers overlapped with two digits?  I have seen plenty that use the three digit route number exits such as around Knoxville, TN.  I-75 uses I-640's exit numbering.

Then, as mentioned before, I-83 uses I-695's numbers even though no exits during the overlap, it is at the split that I-83 leaves I-695 with an exit number and not I-695 leaving I-83.

I-43 on I-894 uses the latter's exit #'s. My prediction is that US(I)-41 will do the same.  I-39 uses US-51/former WIS-78 for the duration of the freeway in WI north of the Cascade Interchange with 90/94.