Wednesday, July 25, 2007

Green flash

RED: Stop.
AMBER: Stop. Unless you're so close to the signal that to stop would be hazardous.
GREEN: Go. Provided it is safe to do so, take care when turning left or right and give way to pedestrians.

And then there's FLASHING AMBER. Appearing at pedestrian crossings, this has exactly the same meaning as a Belisha beacon: Stop if there are any pedestrians crossing the road.

If a GREEN light changes to AMBER as you approach it, what should you do? Slow down and stop, or drop a gear and accelerate into the junction? Only one of these constitutes the correct, safe, legal answer.

The caveat is that the above are the rules for the UK. Other countries' rules might be a bit different, although as far as I know the basic RED = Stop, GREEN = Go is universal.

So what the blue blazes is a FLASHING GREEN supposed to mean? Stop? Slow down? Accelerate? It tells drivers that the lights are about to change to AMBER, and might well encourage them to accelerate to beat the RED. They'll be going too fast to stop safely when the AMBER light appears and thus have a perfect reason not to stop. How sensible can it possibly be to encourage drivers to accelerate into a road hazard? It seems to me to be an exercise in accident promotion. Mind you, I bet that anyone who slows down at a FLASHING GREEN in anticipation of the AMBER and RED will get hooted, and in extreme cases rammed from behind. If there's a need to provide additional warning that the lights are about to change, what's wrong with increasing the AMBER time? It's already three seconds, although if the braking distance chart in the UK Highway Code is to be believed, three seconds isn't enough time to stop from more than around 40kph. Of course, the Highway Code chart was originally written donkey's years ago in the ancient times of drum brakes, no servo assistance, and gripless crossply tyres. The arithmetic produces a deceleration of around 0.3g to 0.5g, which a modern car and a dry road should easily be able to exceed.

Some comments on the Gulf News article cite south-east Asia and Ajman as having the allegedly splendid idea of countdown timers on the signal heads. My own experiences in Thailand and Ajman are disconcerting, at least with regard to traffic lights. Passing through a junction with two or three seconds of GREEN to go, traffic waiting on the other phases suddenly launches into the junction when those drivers can see that there are only four or five seconds of RED still to go.

Amber gamblers and light jumpers do not mix.

Actually, I'm not too keen on the British two seconds of RED with AMBER either because that can also encourage jumping the lights. A change from RED directly to GREEN is perfectly acceptable. Yes, it takes time for the first driver in the queue to react to the appearance of a GREEN. Believe it or not, traffic engineers are aware of this, and factor it into the calculations of cycle time and phasing. Signals are not deliberately designed to cause maximum delay, nor to optimise inconvenience to the maximum possible number of road users. The lights do that all by themselves; they know when you're late for an appointment and do it deliberately. Resistentialism is the word.

Purveyors of the New York Nanosecond might believe that it's compulsory to take off like a scalded cat the moment the lights change. Believe it or not, Monaco excepted, the public road network is neither a Formula 1 circuit nor a drag strip.

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