Roadwar 2000 was awesome. The sequel, Roadwar Europa had some small but useful interface improvements if I remember correctly. Played the hell out of them both. I wish there was a modern equivalent.
The last thing I played that scratched that itch was the online game Dark-Wind. I was addicted to it for some months many years ago. The management aspects and car combat were both great, if only there were a real fleshed out single player version of a game like that.