It is possible to automate your 3 Aspect Signal or even a number of signals by using a series of Latching Relays and Magnetic Sensors. You will need 2 Relays and 3 sensors for each signal. This time the train activates the signal and changes each aspect as it travels along the track. There are three sensors along the track which are activated by the magnet on the underside of the locomotive. The distance between sensors should be at least the length of your train, to create safe isolation blocks between the sensors for the trains to travel in.