Arduino: Simple Traffic Lights [MINI PROJECT]

This is a simple Arduino circuit that imitates a traffic light controller. It's intentionally made very simple so that it's easy to understand the code.

Once you have understood it, try to expand on the code so that it behaves more like real traffic lights. Ex: Real traffic lights never jump straight from red to green. Instead, they light up the red and yellow for a bit, before turning on the green light.