"Matty F" wrote in message
...
So, you are driving along at night and you reach traffic lights which
are red for you. Nobody else has been through the intersection for 10
minutes or more.
Why do traffic engineers make you wait at the red light for 10 or more
seconds before the green light for the cross road changes to orange?
I've spoken to a traffic light engineer and he has no good reason for
the delay, which can easily be set to 0 seconds. But they don't do
that, just because they have always had a delay. Are they stupid, or
is there a good reason for the delay?
I'm not actually that impatient, but there is a situation where public
transport has a tight schedule to keep, and the extra 10 or 20 seconds
on every trip does make a difference, and is a waste of time anyway.

The waiting time for the lights to change that you describe is the period
between green ending one way and green appearing the other is known as the
intergreen period.

The length of the intergreen is determined by the particular circumstances.
Probabably the junction you mention has a high record of red light runners
or some other factor.

Have a look at these four papers which provide a useful introduction and
explanations of the intergreen and other periods in the cycle (second paper
in list):

http://www.dft.gov.uk/pgr/roads/tpm/...fficco4102.pdf
http://www.dft.gov.uk/pgr/roads/tpm/...fficco4103.pdf
http://www.dft.gov.uk/pgr/roads/tpm/...fficco4104.pdf
http://www.dft.gov.uk/pgr/roads/tpm/...fficco4105.pdf

The above papers are all on this page:
http://www.dft.gov.uk/pgr/roads/tpm/...signals/tcbls/


Other computer control programmes have been developed for more complex
situations such as linking several sets of lights on the same road or for
co-ordinating control of lights in urban areas to prevent gridlock.

Explore the other papers he
http://www.dft.gov.uk/pgr/roads/tpm/...gnsandsignals/

This page on American traffic lights is fairly interesting:
http://en.wikipedia.org/wiki/Traffic_lights

Roger R