Late at night, the traffic lights on Finchley Road at the junction of West
Heath Avenue often go red for a couple of seconds before reverting to green.
This is far too short for another traffic or pedestrian phase to have
occurred in between. It seems that sensors facing into the side roads detect
that there is no traffic there and that this causes the green phase for the
side roads to be skipped, but unfortunately the other lights have flipped to
red before this decision is made. Surely this must be a mistake rather than
design.

How are the phases of traffic lights controlled anyway? Is there a program
inside them written in some standard programming language, and someone has
put the IF statement in the wrong place? I would have guessed that the
danger of conflicting greens would have prevented the control sequence from
being written in a standard language and that something much less flexible
would have been used, which would have prevented the error I see at this
junction.

"Basil Jet" wrote in message
...

Late at night, the traffic lights on Finchley Road at the junction of West
Heath Avenue often go red for a couple of seconds before reverting to
green. This is far too short for another traffic or pedestrian phase to
have occurred in between. It seems that sensors facing into the side roads
detect that there is no traffic there and that this causes the green phase
for the side roads to be skipped, but unfortunately the other lights have
flipped to red before this decision is made. Surely this must be a mistake
rather than design.

It is quite common for lights to run though a short cycle when they have not
been triggered for some time. I presume the controller is running some sort
of error check sequence.

Colin Bignell

On Thu, 16 Jul 2009 00:23:13 +0100
"Basil Jet" wrote:
red before this decision is made. Surely this must be a mistake rather than
design.

Don't bet on it. perhaps it wasn't intentional to start with but when it was
realised it would slow traffic down they probably decided not to fix it.
The lights on the purley way in croydon still go red to let imaginary cars out
of empty shop car parks and industrial estates at 1am. Don't tell me thats
not done on purpose just to slow down traffic who might be trying to get a
move on on an empty dual carraigeway. You're not allowed to get anywhere
quickly in london.

How are the phases of traffic lights controlled anyway? Is there a program
inside them written in some standard programming language, and someone has

They probably used to run off an 4 or 8 bit microcontroller with the program
written in assembler, but these days it seems that you can't be a self
respecting embedded systems designer without specifying that the hardware must
be a PC running Windoze because the only thing you can code in is VB.

B2003

On 16 July, 11:39, wrote:
On Thu, 16 Jul 2009 00:23:13 +0100

"Basil Jet" wrote:
red before this decision is made. Surely this must be a mistake rather than
design.

Don't bet on it. perhaps it wasn't intentional to start with but when it was
realised it would slow traffic down they probably decided not to fix it.
The lights on the purley way in croydon still go red to let imaginary cars out
of empty shop car parks and industrial estates at 1am. Don't tell me thats
not done on purpose just to slow down traffic who might be trying to get a
move on on an empty dual carraigeway. You're not allowed to get anywhere
quickly in london.

How are the phases of traffic lights controlled anyway? Is there a program
inside them written in some standard programming language, and someone has

They probably used to run off an 4 or 8 bit microcontroller with the program
written in assembler, but these days it seems that you can't be a self
respecting embedded systems designer without specifying that the hardware must
be a PC running Windoze because the only thing you can code in is VB.

B2003

I should report it to TFL for London. I had a similar problem at a
junction a couple of years ago. it turned out the sensor for
detecting cars was broken so between 2200 and 0600 it would not let
any cars out of the side road. Had to pass through a red light
(carefully) with the permission of the police car who was waiting
behind me.

In article ,
wrote:
Don't bet on it. perhaps it wasn't intentional to start with but when it was
realised it would slow traffic down they probably decided not to fix it.
The lights on the purley way in croydon still go red to let imaginary cars out
of empty shop car parks and industrial estates at 1am. Don't tell me thats
not done on purpose just to slow down traffic who might be trying to get a
move on on an empty dual carraigeway. You're not allowed to get anywhere
quickly in london.

It's probably done on purpose on grounds of cost: lights with a
fixed (or timed) pattern will be cheaper to buy and maintain than
lights with sensors etc.

--
:wq

On Thu, 16 Jul 2009 17:05:16 +0100
Mike Bristow wrote:
of empty shop car parks and industrial estates at 1am. Don't tell me thats
not done on purpose just to slow down traffic who might be trying to get a
move on on an empty dual carraigeway. You're not allowed to get anywhere
quickly in london.

It's probably done on purpose on grounds of cost: lights with a
fixed (or timed) pattern will be cheaper to buy and maintain than
lights with sensors etc.

Except that each set of lights has a rather expensive red light camera
mounted in both directions.

B2003

On Thu, 16 Jul 2009 00:23:13 +0100, "Basil Jet"
wrote:

You can avoid the junction by using the passover

dies

Guy
--
http://www.chapmancentral.co.uk

On Thu, 16 Jul 2009 00:23:13 +0100, Basil Jet
wrote:
How are the phases of traffic lights controlled anyway? Is there a
program inside them written in some standard programming language,

Pretty much, yes. It's on a PROM but I can't remember what language is
used.

and someone has put the IF statement in the wrong place? I would have
guessed that the
danger of conflicting greens would have prevented the control sequence
from being written in a standard language and that something much less
flexible would have been used, which would have prevented the error Isee
at this junction.

Allegedly, a new PROM is created for each junction, while temporary lights
run on a standard sequence. Often the PROM is re-blown after the previous
one has been shown (by long queues) to be wrong.

I say allegedly because at one junction I know, the westbound stops before
the eastbound if no vehicles are detected there. At this junction this is
completely pointless, as both westbound and eastbound traffic is only
allowed to go straight on.

Colin McKenzie

--
No-one has ever proved that cycle helmets make cycling any safer at the
population level, and anyway cycling is about as safe per mile as walking.
Make an informed choice - visit www.cyclehelmets.org.

Colin McKenzie wrote:

at one junction I know, the westbound stops
before the eastbound if no vehicles are detected there. At this
junction this is completely pointless, as both westbound and
eastbound traffic is only allowed to go straight on.

Are there perhaps separate pedestrian crossings for the two halves of the
road?

trainmanUK wrote:

TFL for London.

giggle