Following yesterday’s post on making London more dense, Tim Lund suggested I do a slightly more sophisticated analysis. Planners in London use a metric called the Public Transport Accessibility Level, or ‘PTAL’, which does pretty much what you’d expect.
Rules for things like car parking levels and the density of housing you should build are based on these, because obviously if you’re in central London you have no need for a car and you can justify quite tall blocks of flats, but in low rise suburbia with only sporadic bus services it’s accepted that more car parking and less dense housing is appropriate.
So if you were to follow these rules, how much more housing could you build in London?
First, I took the data for PTAL levels (the map on the left). Then I took my wards, sliced up to remove any areas that cannot be built on, cut out the Heathrow airport too because it was such an extreme outlier, and worked out the median PTAL level for each one (the map on the right). Click for a larger version.
Then I took all the wards where the density was below London’s median. I calculated how many homes you could have, taking the midrange for urban areas for each PTAL level from the Housing Supplementary Planning Guidance (page 32). I deducted the actual number of households from that potential to arrive at the extra homes you could build if you were to bring the areas in line with the planners’ expectations.
This would imply flattening the lowest density half of London and building anew at densities between 80 and 225 homes per hectare.
Here are the results. This map shows all the wards that fell below the median, colour-coded based on the number of extra units you re-built them at the density suggested by the London Plan, using every bit of land for housing:
Obviously nobody is about to demolish such an extensive area and re-build it from scratch, and to take every inch of commercial and industrial land for housing and mixed-use development. The environmental impacts of such a huge demolition and construction program would also be ruinous. So it’s a slightly absurd number. But it gives you an idea of what’s possible. Maybe this is what would have happened if we had a sustainable planning system during the 1930s, when these sprawl suburbs were built?
An interesting ‘part three’ would be to take those areas and see what capacity there is on brownfield site. Sadly, I don’t know of any good up-to-date sources of brownfield data. There’s this data produced by the now defunct London Development Agency, not updated since 2009, which you can see on a map here. One to think about…