but if we have an expanding population, and need more housing, more and better roads are part of the answer
Infrastructure is the answer. You said it yourself, cocoanuttella, when new motorways are built, all they do is get congested.
Rather than continue with the madness that requires people to spend a big chunk of every day in a car, plan towns and cities and suburbs so that schools, shops, doctors, jobs, can all be got to by public transport or by walking or biking.
There is going to come a point, very, very soon, where if we are not to see climate change make all our lives very, very, very difficult, we are going to have to drastically change a lot of things, including our car-bound lifestyles. It's better to plan for that now, while we can.