On Tue, 25 Oct 2005, John Rowland wrote:

Why doesn't Britain extend the "flashing amber" signal from meaning "you
can go if no pedestrians are crossing" to also mean "you can go if no
cars are crossing"?

Good idea.

I'm not entirely sure about using flashing amber, though: rightly or
wrongly, people associate amber with 'go' - and, indeed, 'go, quick!' -
which is not what you want to say here. Also, the main failure modes (in
driving rain, with your windscreen wipers thrashing about, and people's
umbrellas zipping through your line of sight) are going to be only seeing
the lit phases - and so mistaking it for a 'go' sign - or only seeing the
unlit phases, and so not seeing it at all!

I was thinking about this a while ago, and i thought that the best thing
might be to use shape - build red lights with two elements, an inverted
triangle and a circle enclosing it, like an upside-down version of this:

http://www.analyzemath.com/Geometry/...cumcircle2.gif

When you mean 'stop', light both bits; when you mean 'probably stop, but
go if nobody's coming', you light the triangle. The idea here is that the
probably-stop light looks like an illuminated version of the existing
'give way' sign, which will hopefully trigger the right behaviour in
drivers who see it. And, since it's solid red, the main failure mode is
going to be to mistake it for a circular red, which is fine - it's always
safe to stop at a probably-stop. The downside, of course, is that you need
to build entirely new, and more complex, lights.

If you want to use existing lights, then i'd say you need something which
includes a solid red: that means 'stop', giving fail-safe behaviour if a
driver misses the other element. Ideally, you'd then have another element
which doesn't mean 'go' on its own, to give fail-safety if the driver
doesn't see the red. The trouble is, there isn't anything like that - all
forms of green mean 'go' and, despite what the highway code says, so do
all forms of yellow. Perhaps a solid red + briefly flashing green would
do; the quick pulses of green wouldn't be enough to let anyone think it
was a solid green, but would be seen by a driver who was stopped at the
light.

All that said, isn't the real solution to make the lights (or rather, the
junction) sensor-controlled, or perhaps better-sensor-controlled? If the
junction knew there was a queue of cars waiting to go one way, and cars
were only a few a minute the other way, it could just change its lights to
let them through.

This could then be used on numerous traffic lights late at night.

Or at any time and place where this pattern of traffic occurs. Mostly at
night, granted.

Why has Britain never copied the Japanese idea of having a digital
countdown above traffic lights? Surely it would increase capacity, and
also give drivers free time to have drinks or change CDs instead of
staring at the red light.

Maybe there's a worry that if people know they can go in 1 second, they'll
go right now, since it's bound to be safe, isn't it ...

tom

--
If a scientist were to cut his ear off, no one would take it as evidence
of heightened sensibility -- Peter Medawar