You might as well go live in a desert. Plenty of land out there and I'm sure the cost of trucking in water would be much less than creating a livable environment under the surface. What you're suggesting would not be worth it unless we actually ran out of surface space.
While I'll agree with you, I'd like to point out that many intersections operate by using switches underneath the road that detect the weight of a car in order to trigger the intersection. I've ridden up at some intersections without a car and had to move to the sidewalk simply because I couldn't trigger the switch and there were no cars on my side.