Chapter 3 – Part four: A central metropolitan block

Allocation of the permissible generation

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The problem we had to deal with was to allocate the permissible generation of the study area between a number of demands. The ‘essential’ traffic we assumed had to be provided for in full. Because we knew that the balance was not nearly big enough to allow all the trips to be made by car, we first estimated the amount of essential traffic, and by deduction obtained a balance which had to serve for car commuters, car shoppers, miscellaneous car trips, and also for buses. The only way we could proceed was by a process of trial and error. In the calculations summarised below we have, after estimating the needs of essential traffic, adopted an arbitrary allocation for buses. We then worked out the balance available for all optional traffic, and after making another arbitrary allocation for shopping-by-car traffic and other private traffic, we arrived at the final balance available for journey to work by car. This last figure we expressed in terms of the percentage of all persons working in the area for whom space could be found to enable them to commute by car. The figure is 20%.

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We then checked back on our arbitrary assumptions for bus traffic. Having deduced how many could travel by car, and also how many would walk, we knew the remainder would require public transport. Some would travel by tube and others by express bus from ‘picking-up’ points connected directly to the network, so that only a proportion would actually board local buses. The proportion travelling by tube was assumed to be much the same as at present, i.e. about 60%, and of the remainder, about half were assumed to find local buses. In this manner, it was deduced that about 190 buses would have to leave the area during the peak hour, a figure which was sufficiently close to our original assumption not to invalidate the remaining calculations

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The calculations made to determine the number of parking spaces, loading bays, etc., and the proportion and amount of optional traffic are summarised in Table 10.

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The parking requirements and amount of traffic generated are summarised in Table 11. We realise the tenuous nature of some of the assumptions on which these allocations are based, but we think they are broadly of the order that would have to be made in practice. The assumption that 20% of the shoppers would travel by car was made because it led to the same percentage applying to persons driving to work by car. In other words the capacity available was allocated equally, but any other proportions could have been chosen.

Table 11: Number of parking spaces required and traffic generated (complete redevelopment)

* It was assumed that 3,000 dwellings would be needed for the 7,000 permanent residences, of which 1,000 were allocated 2 car spaces eaach and 2,000 were allocated 1.5 car spaces each.

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We estimate that, if there were no restraints whatsoever on the use of cars for journey to work, about 70% of all people working in the area would choose this means of travel. The remainder would be people who for one reason or another use other means of travel. So in fact the allocation we have made would meet almost 30% of the actual demand. By similar reasoning the allocation for shoppers might enable as much as 60% of the actual demand for car shopping to be met, allowing for the fact that many shoppers would already be in the area for some other purpose.