Peter Calthorpe

Calthorpe started from an engineering fact, not an aesthetic preference: the minimum density at which a transit line can support itself without permanent subsidy is known, and American sprawl is far below it. Hence transit-oriented development, TOD: concentrate housing, offices and shops within roughly a ten-minute walk of each station, and leave the rest at lower densities.

His contribution was turning that into a manual a city hall can apply. The Next American Metropolis (1993) does not stop at diagnosis: it sets radii, densities, street sections, use mixes and housing types. He had earlier coined the «pedestrian pocket», the compact neighbourhood unit beside the stop, which is the seed of the idea.

An American architect and planner born in 1949, Calthorpe was one of the founders of the Congress for the New Urbanism in 1993 and has led regional plans for Portland, Salt Lake City, Los Angeles and the state of California as a whole, as well as work in China and Abu Dhabi. With Sim Van der Ryn he had written Sustainable Communities (1986), one of the first books to join urban design and energy.

The Regional City (2001), with William Fulton, argued that the problem is not solved neighbourhood by neighbourhood but at metropolitan scale, where housing, transport and taxes are decided. Urbanism in the Age of Climate Change (2011) quantified the emissions saved by each urban option. He is fairly criticised for the fact that many developments labelled TOD end up as expensive estates next to a station, without the social mix the model promised.