Double-decking freeways. Where would it make sense?

[Plutonic Panda]

Something that's actually being proposed in real life:

I-75/I-85 Downtown Connector in Atlanta

*I-90/94 the Dan Ryan in Chicago.  I don't think there's any space for additional lanes here.

At this point, you'd also have to include the Kennedy Expressway in this.

I was about to mention the downtown connector.

It would be nice to see all of the freeways around LA double decked and connected to the 110 express lanes.

[OCGuy81]

I don't object to double-decked highways, as long as they're concrete, and not defacing a waterfront. I've had enough of 1950s steel girders painted green. L.A. has a stretch of I-110 that has elevated express lanes, which are rather spectacular.

The Seattle waterfront always had the potential of being one of the nicest spots in the city, and now that's coming to fruition. A double-decked I-5 inland would be a good trade.

Maybe double-decking US-26 coming into Portland from the west would be useful, since it's in a narrow canyon. Can you imagine a third tunnel through the Southwest Hills above the existing tunnels? That would be an engineering novelty.

Being Portland, they'd make the top deck of US-26 exclusively for bikes and Tri-Met.

[D-Dey65]

Sunrise (NY 27) and Montauk Highways (NY 27A-Suffolk CR 85) at the Oakdale Merge.

Montauk Highway would be on the bottom, and the west end would include access to Connetquot River State Park.

[HighwayStar]

Hundreds of places. Most major cities in the US could use them. Just a few examples

Philadelphia needs I-76 double decked from I-276 south to I-95.
Dallas needs the Dallas North Tollway double decked, and converted into a freeway as part of the interstate system, perhaps I-145.
Washington DC needs them to complete the original plans for the "inner loop" around downtown.

[02 Park Ave]

Double decking the New Jersey Turnpike with ramps connecting Exit 3 to the North South Freeway would eliminate most wetland concerns when that is done.

[bing101]

https://www.cahighways.org/ROUTE141.html
Vallejo, CA was supposed to have the Waterfront Freeway it was  that went through the west side of the city from I-780. That was until the city of Vallejo agreed to have Curtola Parkway and Mare Island Way. If Waterfront Freeway CA-141 existed the. It would be similar to how San Francisco and Oakland have their Double Decked freeways prior to Loma Prieta Quake.

[Joe The Dragon]

US-12 in lake county can use an freeway deck on top of the local access road

[hobsini2]

*I-90/94 the Dan Ryan in Chicago.  I don't think there's any space for additional lanes here.

The Dan Ryan backs up because of the capacity of the freeways it feeds into, not because of its own capacity. Adding lanes, elevated or otherwise, wouldn't do much.

I-80/94 from IL 394 to I-65, however, could benefit from more lanes, and they'd have to be elevated.

The Eisenhower as well.

[bing101]

Interestingly Manila Skyway in the Philippines is a Double decked Freeway in the middle of the Metro and it is within proximity to the "West Valley Fault" in the Manila area. When I went there I went through Manila skyway to get to NLEX and go to the Central Luzon area.

https://www.rappler.com/technology/features/94600-tremors-app-valley-fault-system-metro-manila/