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Chapter III – part two: A large town

An intermediate network: 208–214

 Novermber 1963    The Buchanan Report    Chapter 3ii  
Contents • Chapter 3ii • An intermediate network

But it is abundantly clear that the scale of the primary network is markedly influenced by the extent to which private cars are used for the journey to work.

An intermediate network

208

The first of the two preceding exercises demonstrates that full car ownership and use in a city the size of Leeds postulates a network of such formidable dimensions that it could not be faced. Yet we are quite sure the public would not accept the other extreme, demonstrated in the second exercise, of confining personal movements to public transport. Between these extremes is a wide range of alternatives. The choice in practice would depend on many factors, from the scope for redevelopment to national and local capital investment policies.

209

But it is abundantly clear that the scale of the primary network is markedly influenced by the extent to which private cars are used for the journey to work. This point is illustrated in Figure 119. This shows how the total flow during the peak hour sharply declines as the use of cars for the work journey is progressively reduced, even assuming (as here that the commercial business and industrial traffic is unrestricted.

210

The converse of the conclusion demonstrated in Figure 119 is that for a given road system having a certain peak flow capacity, if it is assumed that there should be no restriction on the peak period use of essential vehicles and cars for shopping and other non-work purposes, then the proportion of all persons who can go to work by car is predetermined.

Fig. 119 Estimated peak hour and daily traffic flows from the central part of the city with varying degrees of restraint on the use of private cars for the work journeys.
Fig. 119 Estimated peak hour and daily traffic flows from the central part of the city with varying degrees of restraint on the use of private cars for the work journeys.
211

Figure 219 also illustrates the same relationships in terms of the total daily flow. The decline in total flow as the use of cars for journeys to work is progressively reduced, is less sharp. Car commuters’ trips form a much smaller part of the total daily flow, even where their use is unrestricted.

212

An authority faced with the problem of deciding what level of traffic to cater for would have many alternatives to choose from. But it is to be presumed, in view of the general demand for unrestricted use of the motor car, that the greatest possible effort would be made to satisfy the demand. This has been the objective affecting our own choice of an intermediate network with which to demonstrate the process of adapting a network to the actual conditions of the city. The case we have considered is one in which the use of cars for the journey to work is fixed at the following levels:

  1. Journeys to the central employment zone (z)—40% of potential demand.
  2. Journeys to the inner employment zones (v, x, y)—70% of potential demand (excluding the central zone).
  3. to the outer employment zone—no reduction.
213

The remaining journeys to work would be by public transport. It is important to note that the percentage figures relate to the potential demand, not to the total number of persons employed. Thus 40% of the potential demand for travelling to work by car to the central zone would represent about 26% of the total persons employed in the centre.

214

The theoretical network for this level of traffic is shown in Figure 121.

Fig. 121 The theoretical intermediate network which would meet about 40% of the potential demand for travelling to work by car in the central zone. The distributors shown in red would need to be built to motorway standards.
Fig. 121 The theoretical intermediate network which would meet about 40% of the potential demand for travelling to work by car in the central zone. The distributors shown in red would need to be built to motorway standards.
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