MOTORING: Making road signs, boring but important


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The making of road signs is a lot more complicated than painting some information on a board and mounting it on a pole at the side of the road. There are many branches of sophisticated science involved, including chemistry, engineering, human physiology, climatology and traffic kinetics… for starters.

The final aim is simple enough: the sign must be clearly visible and easily legible to those who need to read it (e.g. motorists) – in good time to assimilate its information, make a decision and conduct a smooth and safe manoeuvre thereafter. And that’s not so simple when the reader might be moving at speed, simultaneously watching other things on the road, perhaps in adverse weather/lighting conditions, amid other vehicles that might obstruct the view.

To overcome the obstacles and optimise the result, the positioning of the sign and the size of the writing are vitally important, and several other design aspects are somewhere between necessary and helpful – the colour of the writing, the colour of the background, the retroreflectivity and uv-resistance of the paint, the size of the board, the number and meaning of words, the typeface and spacing of the writing, the x-height of the lettering, the height and strength of the poles and board, their distance from the side of the road… and so on.

Happily, our road sign writers don’t have to guess or experiment or practice to get better. The research has been done – extensively and exhaustively, for decades, all over the world – and there are precise and proven formulae for calculating every aspect of every sign on every road. There are whole books (and laws) devoted exclusively to the subject. History books. Technical manuals. Even one, on the human thought processes for the driver, which won a Nobel prize!

The universal design principles are the most tried, improved, tested and proven system available, and they are consistent. You can’t have every council or county or road contractor making different decisions and leave motorists guessing or peering or head-swivelling and emergency braking.

The essential aspect of signs that might be most surprising to laymen (and, it would seem, to some of our contractors and administrators) is how big a sign must be to do its job properly – especially where traffic is likely to be passing at 80-100 kph.

To cut a long calculation short, on an arterial highway a sign needs to be easily readable, with glance-distracted vision,  from well over 100 metres away. To ensure that, each small letter on it must be at least 20cm high (that’s roughly the distance from your wrist to your inner elbow).

There are similar sets of scientific principle – and books of rules – on road markings (add perspective distortions and psychology to the sciences), cambers, corners, brows, junction designs, slip roads and the shape and height-width ratios of speed bumps and rumble strips….

For those empowered and responsible for designing these items for Kenya’s road users, such literature is highly recommended bedtime reading… or internet surfing.

As with almost everything in road transport, getting it right in competence saves much, much more than it costs in corruption, congestion, wear-and-tear, accidents and mind-blowing exasperation. 

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