Use same technology as wireless network or bluetooth or cell phone (but only need short range) or similar method, at each cross road, or in each cell region, set up a wireless receiver which can communicate with cars going through that cross road or cell region. Each car equipped with such device which can communicate inform with the receiver to the central travel signal control system for better traffic signal control, minimize the waiting time of drivers and routing the traffic flow. To address the privacy problem, the device should allow the driver to randomly select a unique device ID or part of the ID and the traffic control receiver assign another part to form a unique ID every time the car first entering through the signal-controlled street region at the beginning of the travel or allow the device to change the ID dynamically for every travel or daily, etc.

The device even can let driver input the destination to allow the central computer algorithm for better optimization of the traffic flow once the system has whole picture of such traffic data.
The center computer collects those signals, its ID, location and time, and calculates the drive direction or destination, then optimizes the traffic signal system. We will have a better traffic signal controlling system, reduce the waiting time, and have better traffic flow routing.