All planned up front.
The end result is that by the time the project is actually finished (usually 4-5 years later) the population density has changed as well the traffic patterns and the project that was planned no longer meets the current needs. So they start the whole process over again. They never catch up to current needs. And we live under perpetual construction. First get the guys to tear up the road. All of it. Then a few months later bring in the guys to lay dirt and gravel. Then the guys come to flatten it. Next they lay down the asphalt. Finally at the end of the project the guys come by and lay down the paint on top of it all. The funding needed for the project is in the billions. Cost overruns abound. And whatever is delivered is already obsolete. Nice.