SAY WHAT YOU LIKE about The Highway Code - the flat prose style, the see-it-coming plot line, the two-dimensional characters, especially in the illustrations - but it flies off the shelves. The current edition was published in November 2007 and, by the end of that year, had sold 181,368 copies, hoisting it to No 74 in the bestseller lists of 2007, between A Short History of Tractors in Ukrainian by Marina Lewycka, and Mercy by Jodi Picoult.

Bear in mind, though, that the 2005 edition, on sale until the autumn of that year, sold 170,593 copies in 2007. The combined total of The Highway Code sales for last year, then, is 351,961 copies, which would lift it to No 15 in the 2007 chart, just above Richard Dawkins's The God Delusion, marginally behind Ian McEwan's Atonement, significantly ahead of Jamie Oliver's Little Book of Big Treats, and utterly beyond Russell Brand's booky wook.

This, note, is fully 77 years after the Ministry of Transport's guide for road users was first published. Other codes may come and go - the Da Vinci, the Moses, the Eternity - but the legendary pageturner stays on, delivering big sales returns, year after year.

OK, so you could argue that its readership is somewhat captive. The Highway Code is one of a small number of books that can be described without hyperbole as “compulsory reading”. It really is (to adopt some more blurb-speak) for anyone who ever drove a car, or even thought about driving one. Accordingly, there is something optimistic (even if perfectly true) about the assertion on the back cover of the latest edition, that the Code is “for life, not just for learners”. There is something optimistic, too, about the latest design's reader-friendly boxes, throwing you forward to later pages. “What parts of your vehicle must you keep clear of snow? Turn to rule 229.”

Yet the old criticism that the authors simply stick to the same tired formula, time after time, simply won't wash. The narrative of the Code develops from edition to edition. By how much, one can gauge precisely from The Original Highway Code which binds together facsimile editions of the first four Codes in all their slim and robustly illustrated glory.

The original Highway Code of 1931, a 24-page pamphlet, depicts exactly eight road signs. The 2007 edition (the 15th) clocks in at 145 pages and depicts 178. It brought in 29 new points of order, including the risk of smoking while driving (bad for your health, obviously, but potentially bad in other ways, too), while introducing a new section of “advice for novice drivers” and new signs for Home Zones and Quiet Lanes - “places where people could be using the whole of the road for a range of activities”, or, as people in London tend to think of it, Soho.

By contrast, driving in the earliest days of the Code appears to have been a sublimely unburdened experience in which one was merely required to keep a mild lookout for bendy roads and schools (amusingly depicted on signs by a flaming torch of learning) and know what a uniformed constable meant when he stood in front of you with his arm in the air.

Call it the golden age of motoring, perhaps - no driving test necessary (until 1935), no speed limits outside built-up areas and no sleeping policemen anywhere, unless they were, in fact, policemen asleep. Alas, it was also the golden age of killing people. In 1931, when there were only 2.3 million vehicles on the road, 7,000 people died in road accidents. Today, with more than 30 million vehicles around the place, the annual death toll is half that, at about 3,500.

We owe this staggering reduction explicitly to The Highway Code, issued and introduced in 1931 by the Minister of Transport “with the authority of Parliament” and intended to “make the roads safer for you and all others who use the King's Highway”. That first edition made no mention of traffic lights, which had started going up in 1926. But it did caution against sheep and “packs of hounds”, and it did pre-empt, by more than half a century, the phenomenon we know as road rage. (“If another driver shows lack of care or good manners do not attempt any form of retaliation.”)

Some things don't change. A level crossing is still illustrated as a wooden gate. The sign for an open crossing still, quaintly, shows a steam train. The table of stopping distances, introduced in 1946, is identical to the table in the current edition, give or take a shift to metric and despite half a century of advances in the development of car brakes.

Yet in so many respects the 2007 Code would be written in a foreign language to readers of those early editions, with its references to “powered mobility scooters”, “congestion charging zones”, “head restraints”, “mobile phones and in-vehicle technology”, “active frontal airbags”, and “Red Route stopping controls.” The sign meaning “no vehicles carrying explosives”, anyone? Bonus points if you can correctly distinguish between a pelican crossing, a toucan crossing and a puffin crossing. And where the current edition has whole pages of carefully inoffensive notes on the likelihood of variously disadvantaged people staggering randomly into your path, the 1946 edition was blisteringly crisp and postwar: “Allow for other people doing something silly at any minute.”

Even so, allowing for differences of tone and content, the thread that links these editions is society. Without the Code, there is (it is no exaggeration to say) only anarchy, death and unregulated behaviour at junctions. It preaches respect for one's neighbour and, if necessary, his horse. It promotes concern for the young, the weak and the infirm, and their horses, too, if applicable. It urges consideration, above all, for those who are less fortunate than ourselves (namely, cyclists).

And though designed to regulate an activity increasingly derided as antisocial, it may yet be one of the most valuable and binding documents we have for the promotion of civil conduct. It certainly seems to be the most widely read.

The Original Highway Code
Michael O'Mara, £7.99; 128pp Buy the book here

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