Why Not Smart Roads?

So smart roads? A road that provides relative location and speed of each vehicle for computational efficiency and avoidance. This seems like the most reasonable autonomous driving scheme. Enter destination. Network provides minimal path for vehicles not to smack into each other as the distance between cars is maintained for safety and efficiency. The only safety drawback I can think off is non-vehicle hazards in the roadway. I realize there are governmental infrastructure requirements, which would stop such an endeavor. It also means less money to be made so less incentive for commercial capital investment. I have a long car commute, and this thought experiment occasionally occupies the drive. What other considerations am I missing?