Don't Car DX close to houses where it might make the locals nervous. Secondly, don't Car DX from office parking lots or anywhere that is posted. There are plenty of good spots close to where you live, you simply have to scout around and be willing to try them out. Apartment dwellers, try DXing from your car right on the apartment grounds. It certainly will be quieter than inside the apartment and you might just find plenty of room for some temporary antennas.
Parks can be good, too.
DXing from small, neighborhood parks will probably be an improvement on your conditions at home. One of the first things I do when arriving in a new city is to get a good map showing all the parks. These are areas where the roads are, but there aren't any buildings. It could be a housing development that went bust early or a commercial area that never filled up with buildings. The bottom line is that no one is driving that way because there is nothing in the area for them to drive to.