On Sat, 16 Aug 2003 11:19:12 +0000 (UTC), Tim Woodall
wrote:

On Sat, 16 Aug 2003 06:48:58 GMT,
Peter Lawrence wrote:
On Thu, 14 Aug 2003 23:30:12 +0100, Robert Woolley
wrote:


They are detectors which use microwaves to 'see traffic' and adjust
accordingly. Microwaves get reflected by moving metal objects. They
don't work well if traffic is generally very slow moving.

So why does anyone think they are useful in London?

My experiments with the ones near me suggest that the sensors are
responsive to both the echo size and speed. In the car I can
get them to trigger at any speed but on the bike I can't stop pedalling
until the point I need to brake hard for the junction. I've had a
few hard stares from pedestrians waiting to cross who clearly think
I hadn't seen either them or the lights until the last possible
moment. 20-25mph seemed to be the trigger speed I needed to be at
in order to trip the lights and still have time to stop.
(the junction is currently being "redesigned" so it will be
interesting to see what happens in the future)


Microwave detectors tend not to be used in central London where
traffic speeds are low.

Their principal advantage over loop detectors is that they don't
suffer the problems of utitilities destroying them when carrying out
maintenance work.

Detectors can be set to be sensitive to cyclists. Close to where I
live, a jogging pedestrian in the carriageway can trigger a detector
at one lightly used of traffic signals.


Rob.

--
rob at robertwoolley dot co dot uk