The UN predicts that, 'India will become the largest country in population size by around 2022, while Nigeria could surpass the United States by 2050'. In the UK Government forecasters expect the population to increase to almost 80 million by 2051, and possibly over 90 million by 2081, as a result of rising birth rate and longer living.

Wherever these people reside has to enable them to enjoy sustainable lifestyles which minimise carbon emissions. The UN states, 'The climate change debate and action often focuses on energy and industrial activity as the key sectors contributing to greenhouse gas emissions. However, the transport sector, which is responsible for one quarter of energy-related greenhouse gas emissions worldwide, with its emissions increasing at a faster rate than any other sectors, must be included in any effective policy response to climate change. Sustainable transport must be viewed and integrated as an essential ingredient in sustainable development strategies. Transport infrastructure lasts for decades, which means that the decisions which local and national governments make today will have long lasting impacts on urban development and form, as well as climate.'  The UK Government Committee on Climate Change reports, 'Transport greenhouse gas emissions continue to be the largest emitting sector, (and) emissions are rising.'

The first of the many sustainability criteria for new homes and workplaces must be permanent way public transport. The occupants of even the most efficient buildings will consume unacceptable amounts of energy and greatly increase traffic congestion if they have to use private cars for everyday journeys. Their housing and workplaces must be in locations connected by excellent and attractive rail services.

New infrastructure costs billions and takes years to build, so it is essential to make full use of the existing network to provide the spines to serve the necessary growth, and to concentrate large-scale development within walking distance of rail stations - either existing or new.

Only after the transport conditions have been satisfied should the other sustainability criteria such as economics, energy, water, waste, food, biodiversity, etcetera be investigated to find suitable locations for truly sustainable development.

For more details visit www.ConnectedCities.co.uk

Camilla Ween RIBA, MCIHT, AoU, Harvard Loeb Fellow, Camilla is an architect and urbanist working at the intersection of transportation and the urban design. Camilla works on city growth, the integration of public transport and the creation of humane urban megacities that are socially equitable and environmentally friendly. She works in Africa, Central and South America and Asia; most recently for the Foreign and Commonwealth Office / UN Habitat Future Cities Programme in Malaysia.

Brian Q Love is a Registered and Chartered Architect, a Fellow of the Royal Society of Arts, a Member of the Town and Country Planning Association and an Associate of the Chartered Institute of Highways and Transport. He is chief executive of ConnectedCities Ltd and a director of Love Architecture, an RIBA Chartered Practice.