Most expensive projects that would come from proposal or feasibility study

[tolbs17]

Not the ones that are currently under construction like the Hampton Roads Bridge Tunnel...

And no projects that are officially dead

https://connect.ncdot.gov/projects/planning/FeasibilityStudiesDocuments/Feasibility-Study_0810A_Report_2015.pdf

This will be massive. If they plan to elevate the express lanes, that would be a HUGE game changer that would be $2 billion while the one on surface will be $1 billion. I think for cost saving they should leave out the elevated plan and just go with the surface plan.

SCDOT said widening I-95 would cost about $4 billion so that's another game changer for there but I have a feeling it's years away and not a main priority.

[thspfc]

Isn't there a massive proposal for I-10, I-45, and I-69 in Houston? Or is that already underway?

[Bruce]

Washington's I-605 study to build a superbypass between Chehalis and Canada estimated a cost of between $42 billion and $50 billion in 2004. Obviously it was not picked up for further consideration.

[SkyPesos]

I-73/I-74

[CoreySamson]

Isn't there a massive proposal for I-10, I-45, and I-69 in Houston? Or is that already underway?

I believe the project would involve a complete rebuild of downtown freeways, removal of Pierce Elevated, moving I-45 to the east side of downtown, rebuilding 4 system interchanges, and various realigning and widening of the roads involved. MaxConcrete suggests this could cost up to $7 billion by itself. I don't think it's already underway, but it is a serious plan.

[Rick Powell]

In Chicagoland, the two most expensive highway projects being recently or currently studied are the I-290 Eisenhower Expressway between I-294 and Racine Avenue, and North Lake Shore Drive from south of the Chicago River to Hollywood Avenue. Both $3B+ and who knows with today's inflation.

[jp the roadgeek]

Widening I-95 between New Haven and NYC has to rank up there given the land constraints and the prices of land in Fairfield and Westchester County.

[jakeroot]

Washington's I-605 study to build a superbypass between Chehalis and Canada estimated a cost of between $42 billion and $50 billion in 2004. Obviously it was not picked up for further consideration.

I didn't realize it was that much, the Wikipedia page suggests it would have only been, at most, around $19 or $20 billion.

It is rather amazing that it would have still cost less than ST3 (something I too support, for the record -- future ST4 as well).

edit: there is this article which suggests an Oregon to Canada freeway could have cost upwards of $57 billion.