[TB6] ☭Beef Chungus☭: Instead of connecting each microcontroller with each other directly, simply connect the composite of the controller to a cable anchor. So the composite output of the controller goes to the front cable anchor of the car, and the input to the rear anchor. Front most car would be the "main" car and that's where the display is hooked up. Hope this helps. :-)

How would you set it up for multiple passenger cars?