Per capita demand for daily travel in a number of developed countries has ceased to grow, which means that demographic change, both growth and ageing of the population, will be the main determinant of future travel demand and traffic levels. The effect of demographic change on travel demand arises through changes in land use, which in turn are affected by planning policy. In particular, how the additional population will be housed, whether on greenfield or brownfield sites, will be important for decisions on investment in the transport system. Increased population density within existing urban areas facilitates access and is best served by public transport. The declining share of car-based journeys in London illustrates the scope for containing traffic congestion and carbon emissions.