The underpass is going to sink into the terrain by default -12. If you want the underpass perfectly flat with your city, say less sunken, maybe try this. Raise the ground +12 from where your city currently is. Place on new surface. Could give you the look your going for.

I can normally raise and lower with page up and down as well. but the method above might be better just because there's alot of little pieces involved.

Hello, I am trying to place this but i can only place it underground. I cant move it up or down. is there a fix for this?