But the motorway soon generates new and additional car journeys, the motorway then gets more busy then congested
Roads themselves don't generate traffic. It is the desire and need of people to travel that generates demand for more and more journeys. We have more people working in the UK than ever before, which means more demand for travel to and from work. In the old days it was usually only the father/husband who worked, and many people stayed in the same job for years. This meant it was often viable to live within walking/cycling distance of one's workplace. Nowadays most households consist of several working people, for instance a working wife and husband, with a working son and daughter living with them. It is not viable for this type of household to live close to everyone in the house's workplace, hence the need for travel. In any case with less and less job security, even a single-worker household would have to move house regularly to live within walking distance of their workplace as the likes of David Begg seem to be advocating.
The other cause of increased journeys is greater afluence, as people get wealthier they can afford to travel more. Let's not forget that car journeys themselves are contributing enormously to economic activity and wealth creation. People travelling by car are going to/from work, where they create wealth, provide services and generate tax revenue. Many car travellers are going to the city centre shops, to the pub, on holiday, etc., where they will spend money and contribute towards keeping people in jobs, creating wealth, and paying more taxes in the process. Car use itself creates numerous jobs too in car manufaturing, retailing, servicing and petrol sales, not to mention an absolute torrent of tax income flowing to the state from the motorist. Every affluent city has lots of traffic. It's when there is hardly any traffic, like in the former Communist Eastern Europe, that it's time to worry.
"More roads cause more traffic" is a simplistic argument of anti-car extremists, who are to roads what Beeching and Thatcher were to the railways.
The other big irony is that so many anti-car types actually have cars themselves. Most anti-car politicians have luxury chauffeur driven vehicles provided at the taxpayers expense, or in Ken Livingstone's case taxis paid for through a lavish taxpayer-funded expense account.
The bottom line is that we need
all forms of transport to be good, most people travel by train, buse, car, taxi and by foot at some point.