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The funny thing about technology is that most of the time, progress grinds along incrementally – but then suddenly, even unpredictably, there's an explosion that changes our entire world. Take two technologies that have a lot to do with cities and city life: transport and communications. And, since we're looking forward 20-30 years, let's go back 25, to 1978.

In 1978, cars looked and drove much as now. Fewer had fancy add-ons like power steering and automatic transmissions and air-conditioning – but you could get all those things, if you were willing to pay for them. They lacked smart chips under the bonnet, or elsewhere – but those have just made the car more sophisticated, and sometimes more infuriatingly difficult to operate. (Just imagine: in 1978 you could rent a car, turn on the radio and twiddle a dial to find a station). The motorway map was recognisable. The first high-speed Inter-City 125s were operating between London, Bristol and South Wales. Planes looked and flew much as they do now; the 747s were already flying the world.

In transport, incrementalism has ruled.

Not so in IT. If in 1978 you were technically savvy, a geek in fact, you could buy a video recorder, but you'd have a hard time to find anyone who could tune it. You might just find one of the first PCs, being produced in handfuls in little workshops around the San Francisco Bay area.To enjoy the internet, you'd have to be a member of the Pentagon top brass: it was called the ARPANET, it was strictly for defence purposes. Mobile phones you might find discussed as a future possibility, but only in magazines for anoraks. For the world-wide web, you'd need to go to a particularly imaginative science-fiction writer.

So it's here that cataclysmic change has occurred. And will, almost undoubtedly, continue to occur: the big changes will come through the rapid profusion of nanotechnologies [The world's tiniest tweezers], producing computing systems so small that they could be embodied inside our heads, coupled with speech recognition allowing us to communicate directly. Someone rightly described the web as a huge prosthetic addition to the mind; but imagine how much more effective it would be implanted in the brain as an infinite extension of human memory. Clive Sinclair, the British computer pioneer, memorably said years ago that he saw computers of the future as little animals nestling on your shoulder; nanotechnology could make them into something as tiny as a speck of dust on your coat.

But will transport technology, too, progress incrementally and thus almost unnoticeably? Here, we could be surprised. The car could change more fundamentally in the next quarter century than in its entire first century: first through the rapid development of alternative energy sources, most probably, though not exclusively, the hydrogen fuel cell; and second through information and control technology to automate its operation, at least on main roads.

If the Docklands Light Railway and the Central Line in London can operate automatically, with a human being present merely to open the doors and reassure the passengers, if aircraft increasingly fly by wire, taking off and landing themselves, it's hardly fanciful to imagine that cars could do the same. Already, in California, we've seen cars driving themselves almost bumper-to-bumper along a specially equipped lane of a busy freeway. Coupled with sophisticated electronic tolling facilities, this could transform the way we drive.

But what would be the impact on cities and on urban life? Paradoxically, the eco-car – hydrogen-fuelled, non-polluting, automatically controlled – could turn current transport debates on their head: there would no longer be the same objections to the spread of car ownership and to the car culture, and our motorways could take much bigger flows of traffic without the threat of total gridlock. And that, in turn, would remove one of the objections to long-distance commuting and the spread of people and homes deep into the Countryside. Couple that with IT that would allow us all to intercommunicate and to generate knowledge anywhere we happened to be, this could at last achieve the promise of cybercottage life that has always proved a chimera – so far [Meades160].

But will it? That will depend on human psychology. All the evidence so far suggests that the more we e-communicate, the more we find a need to communicate face-to-face. It was no accident that the invention of the telephone was followed by the first skyscrapers in Chicago and New York. Don't bet on the death of the city just yet – certainly not by 2025.