Having thought it over some more, I think multidrop RS485 using async serial protocol might be better because of the long cable runs, with an attiny84 at each signal. If you use Cat 5 cable (or preferably Cat 6 for its lower resistance), then depending on the power requirement of the signals, you might be able to use 1 pair for the RS422 and the remaining 3 pairs for power. The attiny84 has enough pins to connect all 4 lights, the RS485 transceiver, and the switch.