CrossRoads:
Wouldn't need address assigning either - just pass message on to next module indicating "I'm done, your turn".
I believe there are roadside hazard warning lamps as used on the top of lines of traffic cones that work on the principle of a simple radio trigger - each one flashes and then broadcasts a pulse that triggers the next one. I suspect it would use a simple tuned receiver / transmitter and a hardware timer rather than a microcontroller, though. Anything involving thousands of separately addressable units stretched over half a mile would need several thousand dollars worth of control equipment, or vast quantities of wiring. It's all technically feasible but doing it cost effectively and reliably would be the trick. I don't suppose you'd be happy with a solution costing thousands of dollars that crapped out after a couple of hard winters.