You can have a lot of fun with a tiny traffic light using an Arduino and three different color lights. There are bunch of things you can do to build on it.

- 3d print a stand (here's one I did https://github.com/SalvatoreT/howmm/blob/master/week06/Traff...)

- incorporate an infrared sensor + infrared light to simulate triggering the red -> green flow

- make an intersection with each of the lights working together to show the right thing at the right time

- add a crosswalk