Concrete driveway thickness??

I just had a new 112' stamped cement driveway installed. The first 15 feet are part of the city's easement. The city required the easement to be 6" thick. The rest of my driveway is 4" thick. The cement is 3000psi and contains fiber mesh. The city requires the cement to contain a certain amount of fiber mesh so the contractor had to provide documentation to the city before they would sign off on the driveway. The city also required the driveway base to be lime rock which is the same base used for all roads around here. I also asked the contractor to put rebar mesh down just to make me happy. If the city required their part of my driveway to be 6" then I would have gone with 6" for the entire driveway for a heavy coach. The distance from the cement plant to my home was 54 minutes and 4000psi cement sets up to fast for me to have a stamped cement driveway. It was 95 degrees when my driveway was poured.