You can’t measure safe driving in miles per hour

Larry Girling, a Speed Awareness Workshop instructor, muses on speed

I drove back from the December meeting with a resolve to write a piece for the Master Tutor concerning speed, aware that our Vice Chairman had indicated that he was similarly minded to write on the subject.

The heading I have chosen may be, perhaps, more suitable for Brian’s piece [Ed - I prefer Brian’s title!], but as it is a quote from the late Paul Smith, who sadly passed away on 13th December 2007, I consider it appropriate here. Paul was the founder of the Safe Speed campaign, and whether or not you agreed with his views, you had to admire his passion for the subject.

Anyway, back to my initial thoughts. Have you noticed that the Highways Agency have recently taken to using those huge roadside matrix signs to display information that they consider will be helpful to us motorists? One I pass quite frequently when leaving Exeter and heading west tells me that Bodmin is 63 miles distant, and that I will reach that town in 60 minutes.

Now it has been more years than I care to remember since I studied mathematics, but I make that an average speed of 63 mph. We don’t have motorways down here in Cornwall, and the route involves a mixture of dual and single carriageway roads. I’ve never timed it but I reckon I’d be pushed to achieve that average speed.

But as I was saying (this is sounding more and more like one of Ronnie Corbett’s jokes, isn’t it?) driving back from the December meeting I spotted another of these signs informing me that the distance to a particular junction was 42 miles and that I would reach it in 36 minutes.

This was more than my maths could cope with and I resorted to using a calculator when I next stopped at a service station for a break (after driving for two hours, you understand). The average speed required was apparently 69.999996 mph. I checked my on-board computer and my average speed from Walsall had been 57 mph.

So what is the point of this, presumably, Government instigated information? The motorist will believe it and get to the half way point behind time. So what does he (or she) then do? Why, “puts the right foot dahn” of course!

Ok, you and I know the information is gathered from the TrafficMaster network. Which I am a fan of, and have used, ever since its inception. It is, after all, the basis of the SmartNav system I have installed in my two tuition cars. But in the car, the lady merely says “there are no known traffic problems on your route”. Fine, so I carry on driving at the speed I judge to be appropriate. Why can’t the huge matrix signs say the same?

But what is an appropriate speed, I hear you ask? Here you will find yourself bombarded with conflicting advice. According to Roy Buchanan, the Principal Road Safety Officer for the London Borough of Sutton “The A30 across Bodmin Moor is a dream road. It would be illegal but not dangerous to cruise at 100 mph along some stretches” [1]. Thank you, Mr Buchanan, but I would prefer it if you would confine your cruising to roads in your area and not mine.

As I am sure many other IMTD members do, I instruct on the Speed Awareness Workshops. A particularly apt title, I feel, with the objective “To develop your existing knowledge of the consequences of speeding”.

One of the exercises is to imagine a scenario where a driver is travelling at exactly 30 mph in a 30 mph limit. He (or she) is overtaking a stationary bus which is thirty feet long. As the driver reaches the rear of the bus, a child runs into the road from behind the front of it. I dress up the scenario by saying that the car is in first class condition - ceramic brakes, ABS, brand new tyres etc. The weather and road surface is good and the driver is mentally and physically alert.

So the question is will the driver be able to stop? The consensus in the group is, usually, no. The differences arise when I ask at what speed will the car hit the child? Until someone remembers that the ‘thinking distance’ at 30mph is (you’ve guessed it) thirty feet. I then move the child to forty five feet and one inch from the front of the bus and the impact speed becomes zero.

I then repeat the exercise for different speeds until we discover that the impact speed at an initial speed of 40mph is 26+ mph. Near enough the posted limit. The “I was only doing 39” brigade are usually quiet at this point.

So the speed you and I choose to drive at is our personal responsibility.

I will close with a quote from the new edition of Roadcraft: “Next time you take a significant corner on an open road, imagine there is a pregnant woman with a toddler in a pushchair about to cross the road just beyond your limit point. Does this alter your driving?” [2]