Beyond the Big Blob – Outside the first 15 Minutes – The Real Challenge of Zero Carbon Strategic Plans

Soon we will see consultation on the Arc. The reactions are predictable. How big a blob, how many homes, only a few will use the railway station, what about outside its walkable catchment, if large wont then it be car dependent sprawl?

These are good questions. Will a big blob be like Milton Keynes or be like central Oxford, or Toledo, or wherever?

Planning for the first 15 minutes outside a station old or new in theoretical terms is easy. We have well established typologies at a range of densities showing how that community can be developed in a broadly zero carbon way. I have discussed this on this blog many times. You can imagine a grid of ‘hex bins’ hexagons of 400 in radius.

However there will be few such locations in any area – such as the Arc. The problem is how you develop the hexagon outside the first 15 minute neighbourhood, then the next one. The problem is how you get sustainable development at scale. Indeed I have mapped and studied the whole if the Arc, and several other places internationally using such a technique called ‘planagon planet’ its aim is to investigate options for making global rapid urbanisation sustinable and studyng options to do so.

For a rail corridor you have several options. You can place stops regularly, giving it a metro service. The problem then is you slow fast through traffic, which can demand a four track rather than two track solution. Though the marginal cost of the land acquisition for the extra two tracks is small. You need a metro service however as without a large ridership you don’t get frequent services, and without frequent services you dont achieve a high enough transit mobile split to achieve zero carbon. I remember discussing a ‘turbostar’ model I developed for the Arc with the NIC showing you only got a 30% + mobile split if you had service frequencies of less than 3 minutes a Japanese style digitally signals managed service. I was stunned by the answer that this was planned. This isnt really practical however unless you have a string of closed packed stations with development around them.

Another (complemnetary) option is to have rapid feeder services feeding into to stations – via BRT. This you have to do outside the linear clusters, having development of a density and amount to form a whole town of several planagons not just a single ‘planagon’ of development. You can then use this method to test out various scales and densities of development and how they are distributed around transit nodes and corridors.

Hence it is wise not to talk of blobs and ‘sytrategic locations’ but of places and the patterns of development they should form. Once you have a broad vision of the kind of place and the kind of pattern, only then can you go on to dicuss where they should be pinned on the strategic map.

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