Why is the signal always red?
or the signal is always greener on the other side.
The Denver Regional Council of Governments put together a primer on signal timing (get it here). The brief pdf does a great job of explaining how traffic signals are timed and the trade-offs involved when developing timing plans – all in layman terms with great graphics.
I wish I would have had this when I was the traffic engineer for the city of Maple Grove. I would have put it on our website and pointed residents/elected officials to it when they had questions/complaints about our signals.