On Sat, 21 Feb 2015 22:14:47 -0000, JNugent wrote:

On 21/02/2015 17:38, Tough Guy no. 1265 wrote:

This has been asked before, and I only got stupid answers like "the cars
need time to stop". Why is it when you press the button on a pelican
crossing (just a basic one, not at a junction), there is always a delay
of about 10 seconds before the lights for the cars change? And no it
isn't to allow the cars time to stop. It makes no difference if the
light sequence starts at or 10 seconds after the pedestrian pressing the
button. Just think about it.

Please sir!

I know the answer to this one!

The delay is built-in in order to damp the effect of several pedestrians
(or even one) pressing the buttons repeatedly in quick succession.

If the circuitry responded immediately (I know of no reason why that
couldn't physically be arranged), at a point where pedestrians crossing
the road arrived in a near-constant stream, and bear8ing in mind that
the lights must allow the individual a reasonable amount of time to
cross even if he is disabled or has restricted mobility, the lights for
traffic would be red for too much of the time and green for an
insufficient time. At very busy locations, the lights might be red for
traffic more or less constantly during the rush hour, which isn't a good
thing even for pedestrians, many of whom intend to travel (or have just
arrived) by road vehicle.

What an odd way to program it. Surely all it needs to do is to leave a gap AFTER the car lights go green again, before it can react again. Unless it has VERY simple circuitry, like it's made of 555 timers or something, this could be done just as easily.

alt.electronics added.

--
There once was a time when all people believed in god and the church ruled. This time was called the Dark Ages. -- Richard Lederer