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The logic of the London density matrix?

Dr. Malcolm Hockaday 09 Nov 2015
It seems like London alone has a density matrix, such that the distance from public transport dictates the density approach to be applied when residential development schemes are assessed.  Over the 20 years from being introduced as regional guidance in the first London Plan, the matrix has sought “…to reflect and enhance existing local character by relating the accessibility of an area to appropriate development…”.  But does it? It’s since been regularly overtaken by ‘exceptional design quality’ to achieve higher densities in scheme approvals – but if design quality is a basic requisite, this should be happening everywhere in London anyway. The real outcome is that: fewer homes are being built than would otherwise be achievable on sites in inner London, if they are a just few more minutes’ walk from a bus route or tube station; and the potential occupiers of these unbuilt extra homes therefore have to live further out in the suburbs (or beyond). As an indicator, a Zoopla advertisement in October indicated that nearly four fifths of homes are beyond a reasonable walk to/ from a railway station.  So that overall journey times could easily be 30 minutes longer or more each way, day in, day out for Londoners.  Bad news for Londoners and bad news for sustainability, travel costs and congestion. It is often the effectively binary choice between PTAL1-3 or PTAL 4-6 which can virtually double the acceptable density.  If the London Boroughs as local planning authorities (LPAs) accepted a little more subtlety in interpretation this would not matter but they are all too often placed under pressure by objectors if considering accepting schemes at ‘above the maximum density’.  The London Boroughs are at the front line of this policy judgement and applying it to proposed developments, when it is the Greater London Authority (GLA) that has set the bar wrongly. Even the 2006 review of the matrix’s operation – only two years after its introduction – showed two-thirds of schemes even at that time as being at densities above the maximum for the PTAL rating. Then the GLA’s 2012 own review of housing density policy conducted mainly by consultant architects identified some of the weaknesses of the PTAL system as being related to public transport access but not to whether the nearest routes actually go to where people need to travel.  It suggested using parallel assessments about ‘access to opportunities and services’.  However, it also puts the true relevance of density quite eloquently: “On the one hand it informs everything to do with housing design and management. On the other hand, the actual density calculation of an acceptable development … is a product of all of the relevant design and management factors; if they are all met, the resultant density figure is what it isand is arguably irrelevant.” So why is the policy still in the Plan? The vocal pressure for densification across all parts of London should be recognised as: a) worthwhile for securing the more efficient use of urban land; b) a means of shortening journeys to work and travel times to services; and c) avoiding some of the overspill into the wider South East. Recognition should be given, too, to the fact that the traditional suburbs are not really likely to see massive change as a result of the policy shift. So the Zoopla advertisement crystallises the failure of the approach, with new developments being unnecessarily constrained and leading to far less attractive long distance commuting. The density matrix should therefore be abandoned in the next review of the London Plan.  It should be replaced with an approach of ‘optimisation’ as recommended by the 2012 review as, ‘developing land to the fullest amount consistent with all relevant planning objectives’. Then there would be a planning policy framework in place in the capital within which the development sector could operate and to maximise the use of scarce urban land for homes to house sustainably the rapidly-increasing London population.

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