The Arduino Pro Mini used to control the traffic light is not only responsible for playing the tones through a piezo speaker, but as you might expect, for firing off the relays which ultimately ...

Nothing comes close to the awesomeness of this traffic light server monitoring system which has been created using a little Arduino wizardry ...

To make things a little easier on yourself, Arduino shield-maker 1Sheeld shows off how to hack a clock to change color depending on traffic conditions.