Central control creates more problems than it solves. Allowing cars to go a lot faster makes little sense because of how energy inefficient it is. Your average car tops out its fuel efficiency around 55 miles an hour, and declines precipitously beyond that point. Cars that can easily go 200mph and do it efficiently aren't even on the drawing board today. You'd have to address that before it makes any sense at all to have central control. As gturner said, there's also a much higher accident risk at such speeds. The only place such high speeds even make sense is intercity/interstate highways, in which case you'd be much better served having high-speed trains instead. Autonomous self-driving cars exist today and could be a common sight in the next decade or two. Central control of them makes very little sense, though.