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A PHYSICIST WRITES . . .

(March 2008)

This month I am going to talk sense. I mean I want to discuss different sorts of sense. As drivers, one that we all need of course is road sense. I can remember acquiring a little piece of this at the age of seven or eight. My father and I sometimes cycled together along a quiet road and then took a right exit at an ordinary roundabout. One day he pointed out that we really ought to be passing the other two exits first, instead of heading straight for the third! This came back to me recently when, driving over a wide roundabout, I passed a young man on a bicycle zooming the other way, on my side of the central island.

Hence the question that I put to Peter Rodger, Chief Examiner of the IAM, when he spoke at our Thames Valley Group meeting last month: I learned road sense during many youthful years on bicycles, but plainly todayís youth fail to do the same on theirs, so how do driving instructors cope with the task of instilling road sense into them as they start to learn to drive?

I suspect Peter Rodger didnít quite catch the end of my question, because his answer focused on parental attitudes and shortcomings. Some members then responded that many children are put through Cycle Proficiency training. Very good ó but I still wonder how driving instructors set about teaching basic road sense when this does turn out to be lacking in their pupils.

An important part of road sense is speed sense. Taking your eyes off the road to look at the speedometer can be risky sometimes, so you try to judge your speed from how fast the surroundings appear to be moving past. But as Iíve pointed out before (October 2004), when these Ďsurroundingsí are the sides of the road, they give you a different indication of speed depending on whether the road is wide or narrow. And then sometimes all you can see around you are other vehicles on the motorway: what help are they, as you try to estimate your speed? So you do have to glance down and read the speedometer occasionally.

On second thoughts though, neither judging your speed nor reading it give you a true Ďsenseí of it. Sitting in the driving seat, sealed into your car, you might as well be in some sort of driving simulator looking at a screen! To know what your speed really is, you need to feel the wind in your face, and some of the roughness of the road in the seat ó as I did on my last, fast, drop-handlebar bicycle, long ago...

Then thereís energy sense. I explained back in April 2006 what a devastating quantity of kinetic energy your car possesses even at 30 mph. I also pointed out that if your speed doubles, the kinetic energy quadruples! And then if you come to rest in a hurry, all of this energy has to be absorbed and dissipated as heat by the brakes. Unless of course itís something else that stops you.

If I mention acceleration sense, most of you will know what Iím thinking of: the skill of planning an accelerating manoeuvre and then completing it at just the right time and speed and place. But more often, surely, what is needed is deceleration sense. A good example of applying this is when youíre approaching a busy roundabout and trying to adjust your braking so as to slot into a gap thatís coming round.

Or suppose that when such a roundabout first comes into view, several vehicles are ahead of you: do you think of taking your foot off the accelerator as soon as you see them? After all, itís unlikely that they will clear out of your way before you get there.

And if youíre on a straight road and a vehicle emerges in front of you and begins to accelerate, is it obvious to you that the sooner you react and lift your foot (and maybe even touch the brake) the less you will actually need to slow down, while you are catching up with the other vehicle? Thatís deceleration sense!

Another sort that isnít often talked about is gradient sense. To me this means anticipating the effects of a slope (uphill or downhill) rather than just reacting to them. Going up, not only will your acceleration naturally be less than on the level ó unless you apply more gas ó but also you may have to avoid block-changing (1st gear to 3rd and so on), if this is your habit. Less obviously, can you use the incline to slow you down when necessary, instead of braking? Though if you do, remember that a driver right behind might still be grateful for just a touch on the brake pedal to illuminate your brake lights.

Going down, it only takes a slight gradient (depending on the gear youíre in) to allow you to maintain your speed without depressing the accelerator. On steeper hills, you may like to remember what I calculated for you in September 2005: whatever the indicated percentage gradient is, your minimum braking distance will rise by about twice this (eg, by 20% if the gradient is 10%), compared with on the level in the same conditions.

Donít forget that hills also affect your fuel consumption! I astonished even myself in September 2006 when I worked out that a Ďnormalí figure of 40 mpg drops to 20 mpg (very roughly) on a mere 3% upward slope. If the gradient is 10% the consumption becomes about 10 mpg ó and you can only compensate for this a little bit by coasting downhill the other side (thatís if there is an other side).

Lastly, letís consider junction sense: the disappearing art of not blocking road intersections. To reverse this trend, should even more junctions be given yellow hatching? On the contrary, I think all road signs, markings and lights should be removed, and obstructing any intersection should become an offence. Culprits would be easy enough to catch, because they would be stationary.

After all, as was argued on BBC2 Newsnight recently, we wouldnít approve of yellow hatching disfiguring buildings, so why do we tolerate it on roads? And last month at our group meeting, Peter Rodger showed us some astonishing film of a totally unmarked junction working perfectly well under heavy traffic (he did mention it was situated in India). He said the absence of road signs and so on brings out our instinct to drive safely and courteously. I rest my case!

Peter Soul

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