You all have kicked some modding ass lately.... Orion, Udon, and now this.... great work and thanks to all that have taken the "fixing" of Simcity seriously.... I truly hope that EA/Maxis has taken note of these things and are holding their heads in (RENEWED) shame.
Was just screwing around with this one here for a bit.. it really works great! Power/Water/Sewage/Traffic can all follow the tunnels out of box. You can even use the non-Udon roads (out of box) for raising and lowering, and agents will use them though since they can't be "upgraded" yet, the graphic looks funky where it just cuts into a mountain and disappears. Be careful of your directions, I had two one way streets leading up lol and residents wouldn't move in to the R zoning on the other side of the tunnels.
Also, just a tip I figured out from the practice. First, I used a udon MD to lead up to the point where I want the tunnel to start, and a udon MD at the exit point. Then I added the udon LD (cause I wanted a tunnel) and upgraded that. Perfect. The reason I suggest this is because it seems that if you draw the udon LD all the way, it will upgrade everything and you'll get a tunnel above ground. Once the tunnel (or bridge as the case may be) is upgraded, then upgrade your Medium entry/exits. I hope that this will come with some localization text soon too.
Again, great job!