Ruth Brandon: My second car is a very slow Porsche indeed

On the street where I live we witness, twice daily, a theatre of frustration. Every morning between 8am and 9.30am, and again in the afternoon between 4pm and 8pm (and quite often much later), the road is jammed with vehicles going nowhere.

And what vehicles! Remember those bumper-stickers you used to see on superannuated Minis saying "My other car is a Porsche?" Lots of rich people live round our district of London, as it happens, and for them that's the exact truth. Onlookers are daily invited to admire Range Rovers and Jags and Ferraris, BMWs and Mercedes, soft-top Rollers and Bentleys...

But however much you spend on a car it can only go as fast as the traffic lets it. And in Britain today, that means no faster than all the pissy plebeian little Golfs and Vauxhalls, those low-end Peugeots and Renaults and antique VW vans that are still, for some unaccountable reason, permitted to litter the carriageway. God, the frustration! Jeeves, where's my autogyro?

It's been a long time since car adverts portrayed anyone driving along an actual street - presumably because everyone would know that, if there was room to move, it simply wasn't realistic. For a while they got round the traffic problem with computer-game projections - perfect, empty roads and bridges that sprang out of nowhere. Then there was a brief fashion for deserts.

Now, however, it's all about water. Have you noticed? The new Audi Quattro has to show its paces in the sea, the only remaining space without queues of cars. There's also an SUV that for some unaccountable reason has landed on an aircraft-carrier, where it won't be much use. And the new Vauxhall Astra is likewise heading for the ocean - in this case, surprisingly, to the urgent beat of "Rock Island Line". Hey, chaps, that's a railway. Didn't anyone tell you?

It's hard to figure out why anyone would spend serious money on big, fast cars now that you can't actually drive them anywhere. Yet they do. So obviously the transport function is negligible. Cars now are solely accessories. Of course, this is no new role for them. You knew, if you saw a pink Cadillac in 1960, that it contained either a film star or someone hoping to be taken for one.

Now, though, it's all much more complicated. Few are such clear and wonderful declarations as that of a local cake-shop owner who drives a pale-blue Rolls with gold handles, pale leather upholstery and lacy cushions just like his own cream-puffs, and whose number plate proudly proclaims proprietorship as he parks alongside his emporium.

He, at least, is the real thing. The sad truth is that, mostly, the owners of the dreamboats that hog all our side-road parking-bays are the dullest men in the world. Dentists and accountants vainly hope that ownership of a Porsche Carrera will make them as glamorous as their wheels; tax them, say I, and charge accountants with vanity plates double.