They had an old 110v set of wired traffic lights and I refitted these to work wirelessly from a 12v battery.

This consisted of a control box that sent commands to eash slave traffic light.
The control box consisted of an Arduino Mega, LCD shield and NRF2401 2.4GHz radio transciever - housed in a 3D printed box.
The controller can control up to 4 sets of lights and has a really good working distance.

The traffic lights were completely stripped of all electronics and the 55W halogen bulb were repalced with 3 x 1W LEDs of the required clours (Red, Amber, Green).

The hardware consisted of an Arduino Nano, NRF2401 2.4GHz radio transciever, relays, micro switches for settings and LED driving circuitry.

Version 1 of the hardware was all manually wired and took a long time to solder up.

I also created a version 2 of the hardware using custom built PCBs with a better switch for the settings.

There's also a V3 of the hardware that uses Logic-Level MOSFETS instead of relays. (No images as yet though)