I've been trying to figure this out guys, messing around with the settings and I can't replicate it, so I'm not exactly sure what's going wrong. Sometimes things fall apart when node snapping isn't active, but that doesn't seem to be it. It might be something with how close together I squeezed the tunnels to make it look like a single entrance.

I don't have work tomorrow, so I'll probably have an alternate version up then.

I've the absolutly same problem :( I tried to use the terraforming tools but got no evidence from them

@I tried leveling the terrain several times and had the same issue

CS will use the underground view anytime you are placing something with tunnels. My guess is that there was some slight unevenness in the ground, I made it with very tight height clearances, so a change in elevation that might not be very noticeable could possibly mess it up. I'd go over the ground with the level tool in terraforming, just to make sure the ground's perfect, that should work. If not, or if anyone else is having this problem, let me know.

I'll also make a version out of all elevated segments, with the major road passing over the interchange, which should make it immune to that.

When placing this it goes to the underground view and the places it in a way that's unusable, tunnels showing over roads uneven ground (even though it was placed on flat) creating a really odd tunnel at the end