It is a truth universally acknowledged that the key to tackling urban congestion and pollution lies in persuading residents to choose 'good' transport - foot, bicycle, public transport - rather than take the car. Ken Livingstone will announce improvements to London's public transport when he unveils the consultation draft of the GLA's Spatial Development Strategy next week.
But what will he do to persuade Londoners to cycle or walk?
Valencia - host to last week's conference on the future of cities - has, by default, stumbled upon a particularly successful solution. Faced with the threat of occasional flooding, the city re-routed its river. The decision was born of necessity, but the administration is to be applauded for seizing the opportunity and developing the drained riverbed as a meandering green space. The city gets its sport areas and parkland - but these could have been provided by selling some of the land for development, while holding back areas to be retained as public space.What makes the project visionary is the fact that the river bed has been kept in its entirety.The new map of the city is both familiar and radically transformed. Buildings which were designed with river frontage are still seen to their best advantage. The bridges which straddle the river bed retain their importance as transport routes, but are now also enjoyed as sculptural adornments to the park below - a significant improvement in a city which lists Santiago Calatrava as its most famous son. All new amenities are rendered highly accessible by virtue of the fact that the location of the river is as familiar to locals as the Thames is to Londoners. And the continuous swathe of public land makes walking and cycling though the city efficient, enjoyable and (reasonably) safe.
Clearly, re-routing the Thames is not on the cards, but Valencia's experience is a reminder that persuading people to leave their cars at home is not simply about improving public transport - or even about providing pedestrian and cycle routes. Any strategy to dramatically change the way residents choose to navigate the city needs to be combined with a gutsy attitude to urban design.