Traffic crossing madness

For many years I've wondered why pedestrian crossings have a delay when you press the button?

Today I walked up to Screwfix to buy some screws, believe it of not, and had to cross the road on the industrial estate in the process. Pressing the button causes you to wait what seems like fifteen seconds, just long enough for you to get across the road if there is a break in the traffic before the lights change.

So pressing the button I duly waited the fifteen or so seconds, during which there were no cars coming and I felt like a lemon standing there and could easily have crossed the road twice over. After the delay the lights changed to red just in time for a few cars to come along and have to stop. How many times have any of us pressed the button only for there to be an immediate gap in the traffic so we cross the road and then the lights go red and there is nobody there to cross?

So why do crossings have this strange delay? I think about these sort of things because I'm a bit odd like that. Is it because the designers thought that the cars might be stopped twice in a row if there are more people wanting to cross and the lights would always be red? In which case just put a timer on the circuit so that it can't go red twice in a set period. Then you'd only have to wait if there were lots of people crossing. Drivers would never have to watch someone cross as they approach only for the lights to go red when they've finished.

It's just a thought, but a thought that's been driving me mad for years.