In Cars Traffic Control you are responsible for the traffic control. Only you can take control over the traffic lights and make the traffic look as it should be. Use your mouse to click on the traffic light and change the color. At the beginning it will be easier because it is enough to block two roads and let the vehicles from the other two roads pass by without crashing. However, as you progress there will be no time for that, so you will have to take the risk and complete the Cars Traffic Control mission.