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Saturday, 6 October 2012

"Queue Ahead". The Department of Transport's Big Mistake

In recent years, England's Department for Transport has invested heavily in large electronic signboards which now blight every English motorway (I don't know about Scotland or Wales - I don't drive there). France has done the same, on a lesser scale. Germany has yet to succumb - it is still spending its money on road building.

I don't think these signboards (I think of them as Gantries) can deliver what I guess was promised, "real time information". I think they make the roads less safe.  I think they do not improve traffic flow. If those three things are true, then the Department for Transport should switch off these expensive toys and sell the gantries for scrap.

Let me to try to develop the argument from the example of "Queue Ahead", probably the most common infomessage flashed up - rivalled only by the nannymessage "Don't Drink and Drive".

So somewhere Ahead a camera has revealed a Queue to a Control Centre operative (or maybe a computer program) and the message is flashed down the line, with some time delay which I can't estimate.

If you are not already sitting in a Queue when you read the message - which is then simply fatuous rather than informative - then you will make some response. Some drivers will slow down in anticipation. Other drivers, familiar with Queues Ahead which no longer exist when you get there or Queues Five Miles Ahead, do nothing. This uneven response is dangerous - vehicles are slowing or not slowing in an unpredictable way. That is a recipe for an accident.

By way of contrast, I give this example. Recently, I was driving up the A20 from the Channel Tunnel, in heavy traffic, when suddenly - with absolutely no warning - there was a torrential downpour accompanied by lots of lightning. Visibility dropped dramatically and instantly. Remarkably, not only did all vehicles reduce their speed within seconds - they all reduced to 40 mph (I checked when I realised what was happening). So the pattern of traffic was maintained - no one changed lane because no one needed to. And Nanny was nowhere to be seen.

There was probably a time when "Queue Ahead" made me slow down  but - so often was there no Queue to be found (whatever congestion the camera had found had cleared itself by the real time I got there) or else the Queue was five miles away -  that now I no longer do. "Queue Ahead" is now just an irritant - and irritated drivers are less safe drivers. This is a very good reason for scrapping these signs.

But there are other drivers who respond to "Queue Ahead" and dutifully slow down. They thus contribute to creating a Queue where there was none. This is very easily done.

Think of what happens when drivers spot a police car on Cruise Control at 68mph in the slow lane. The drivers brake. Within seconds a Queue develops, broken only as fast as drivers dare to overtake the police car. "Queue Ahead" has the same disruptive effect as the patrolling police car.

The moral is simple: if you want to keep traffic moving, switch off the signs. And keep police cars off motorways.

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