Highways crossing over themselves

[CtrlAltDel]

I was playing around with Google Maps a bit, and I noticed that just outside Castaic, California, I-5 crosses over itself for a few miles. Looking around some more, I found that I-8 also crosses over itself just outside Yuma, Arizona.

I-5 crossing itself (Image from Google Maps)


I-8 crossing itself (Image from Google Maps)


I had a few questions about this phenomenon.

First, are there any other crossovers like this? I would imagine most would be in mountainous areas, but I couldn't be sure.

Second, why did the engineers who designed these highways decide to have them cross like this? What purpose does it serve?

And finally, is there anything in the MUTCD about crossovers? I noticed that there are no exits from either I-5 or I-8 when they are crossed, but I don't know if that's just a coincidence.

[maplestar]

The only one I think I have driven is on I-85 in North Carolina, between US 64 and Thomasville.

[jp the roadgeek]

I 95 used to cross over itself at the eastern junction of the Baltimore beltway, but it no longer does so after the huge reconstruction project.

[1995hoo]

Autoroute 20 approaching Montreal from the southwest. I'm posting via iPad and don't know of a way to get a map link on here, so I'll edit this later unless someone else posts a link in the meantime.

Edited to add: Map link here– https://www.google.com/maps/@45.4584879,-73.6116237,15z . The satellite view is kind of grainy and you have to zoom in fairly close to see the crossover, so I've linked the map instead.

The I-85 segment shown above has a rest area, with a Vietnam Veterans memorial, in the median partway through the segment. I've heard it theorized that the crossover exists in part to allow for right-side exits from both directions. I have no idea whether that is accurate.

[Mapmikey]

North Carolina also has I-77/US 21 in Charlotte through the interchange with I-85.  Presumably this was to make the footprint of the interchange smaller.

https://goo.gl/maps/b3SPN

Also, I-70 does this within tunnels at MM 125 in Glenwood Canyon

https://goo.gl/maps/6Snq7



Mapmikey

[jeffandnicole]

There's the 495 Helix at the Lincoln Tunnel. 

[dfilpus]

I 95 used to cross over itself at the eastern junction of the Baltimore beltway, but it no longer does so after the huge reconstruction project.

AFAIK, I 695 still crosses over itself in that interchange. The construction of the HOT lanes is supposed to straighten that out, but that has not happened yet.

[formulanone]

The I-65 and I-20/59 interchange in Birmingham shows each lane of travel crosses over (and back) at the other side of the "knot".

[SteveG1988]

Does it count if one is the old route that carries truck traffic?

US 1/9 in NJ crosses over old US 1/9 (Truck 1/9 now) on the pulaski skyway.

[agentsteel53]

There's the 495 Helix at the Lincoln Tunnel.

if this counts, then so does the I-95 cloverleaf in Canton, MA.

[1995hoo]

It occurs to me that an honorable mention might go to the Lotus Bridge connecting China and Macau. Mainland China drives on the right while Macau drives on the left. The bridge is designed to shift traffic to the proper side of the road by having the carriageways crossing each other in a looping configuration on the Chinese side. I'm not sure it's fair to call this a "highway" in the sense the original post uses it, however, which is why I suggested an "honorable mention":

https://www.google.com/maps/@22.1392267,113.5483006,994m/data=!3m1!1e3



Edited to add: Here's a more "standard" carriageway cross-over on I-275 in St. Petersburg, Florida. I've driven this stretch southbound several times but never realized the carriageways cross over each other. I don't know why it's designed this way:

https://www.google.com/maps/@27.7196888,-82.6756372,17z

[hbelkins]

Newfound Gap Road in the Great Smoky Mountains National Park.

[dfilpus]

US 16A south of Mount Rushmore

[Arkansastravelguy]

Newfound Gap Road in the Great Smoky Mountains National Park.

US 441. I-85 in North Carolina crosses itself so they only had to build one rest area.


iPhone

[getemngo]

The I-65 and I-20/59 interchange in Birmingham shows each lane of travel crosses over (and back) at the other side of the "knot".

The I-196/US 131 interchange in Grand Rapids is exactly like this, except only US 131 crosses over itself.

[agentsteel53]

US 16A south of Mount Rushmore

similarly, old US-99 in Oregon, very near the CA state line.

[Alex4897]

There's the 495 Helix at the Lincoln Tunnel.

if this counts, then so does the I-95 cloverleaf in Canton, MA.

If that counts then so does every single interstate that switches highways at cloverleafs and several that enter a turnpike at an interchange.

[hubcity]

Second, why did the engineers who designed these highways decide to have them cross like this? What purpose does it serve?

Hazarding a guess here: the grade/right-of-way for a former railroad or a previously-built highway was only wide enough to support one Interstate-grade carriageway, and could not be made wider, so the easiest way to construct the opposite direction's carriageway was to "thread" it around the existing one using a new right-of-way. (Do I win?)

[agentsteel53]

Hazarding a guess here: the grade/right-of-way for a former railroad or a previously-built highway was only wide enough to support one Interstate-grade carriageway, and could not be made wider, so the easiest way to construct the opposite direction's carriageway was to "thread" it around the existing one using a new right-of-way. (Do I win?)

I-5 is indeed the case.  the northbound lanes were the original Five Mile Grade, and the southbound lanes were added where they could be.

I am not sure about I-8, since historially US-80 followed the railroad west of Wellton, multiplexing with US-95 to enter Yuma.  there may have been a two-lane alignment across Telegraph Pass, though.

[roadfro]

Hazarding a guess here: the grade/right-of-way for a former railroad or a previously-built highway was only wide enough to support one Interstate-grade carriageway, and could not be made wider, so the easiest way to construct the opposite direction's carriageway was to "thread" it around the existing one using a new right-of-way. (Do I win?)

The right of way issue you describe can be a reason. As for the crossover issue, especially in mountainous terrain, the likely reason is that the second roadway had to be constructed in less favorable terrain grade-wise. The second road was likely steeper or curvier, and engineers probably thought to swap them so as to not have trucks going down a steeper/curvier downhill grade. By casual observation of the pic above, this might be the case with the I-8 example.

[hbelkins]

Seeing Cody's pictures of his trip to NYC reminds me of another example: US 33 in Ravenswood, WV.

[roadman65]

I-275 crosses over itself at the north end of the Sunshine Skyway Bridge in St. Petersburg, FL.  Also the FL 112 freeway entering MIA crosses itself adjacent to LeJune Road.

[cl94]

I-76 in Youngstown, OH at I-80. Both directions cross over themselves at least once. Eastbound crosses over itself twice more in the double trumpet.

I-70 in Breezewood, PA (good time to mention that I hate that interchange (if you can call it that)).

If we're counting trumpets, then I-90 east of Albany, NY at Exit B1 and I-76 next to the King of Prussia Mall.

[WashuOtaku]

The I-65 and I-20/59 interchange in Birmingham shows each lane of travel crosses over (and back) at the other side of the "knot".

The I-196/US 131 interchange in Grand Rapids is exactly like this, except only US 131 crosses over itself.

The I-77/I-85 interchange in Charlotte, NC also does this.

[thenetwork]

Also, I-70 does this within tunnels at MM 125 in Glenwood Canyon
https://goo.gl/maps/6Snq7
Mapmikey

As a local who travels thru Glenwood Canyon frequently, the Hanging Lake Tunnels run side by side and do not cross over each other.