This is a very basic traffic light circuit that is built around the TTL family 74145.
The circuit is stepped by a 555 astable oscillator. The rate at which the timer IC changes is determined by the value of resistance.
The Oscillators output is divided by a 74LS90 divider that produces a (BCD) output.
There are four counts for RED, two counts for ORANGE and four counts for GREEN.
A presentation prepared by my friend's friend. I have done no editing at all, I'm just uploading the presentation as it is.