Chapter III – part three: A historic town

Siting the ‘barriers’

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We were now face to face with the environmental management problem. We had, as it were, brought the traffic to the several ‘gates’ of the old city. How much could now be admitted and through which gates? And how could cross-penetration all over the area be prevented? The answer appeared to lie in devising ‘barriers’ to cross-movement which would have the effect of breaking down the whole area into sub-units, each with gates to the network, but without direct connection to each other. The crucial matter to decide was where to place the barriers and how many would be required to have the desired effect.

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To answer these questions it was necessary to understand the traffic-desires as they would be likely to arise, irrespective of restraints, within the old city when vehicle ownership approaches the maximum. We started with the known present-day peak hour flows of each kind of vehicle into and out of the area. We separated these flows between through traffic and local traffic, and also between usage for industry, business, travelling to work, shopping and other private uses. We then applied ‘growth factors’ to each in turn. We assumed that commuters’ cars (in the absence of any major discouragement) would increase by nearly 4 times, carrying almost 70% of the working population instead of about 20% as at present, with a slightly lower number of persons per car; that shopping and other private traffic would increase by about 3 times; and that commercial and business traffic would be about 23 times the present-day level.

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We were able to trace where, and in what proportions, this traffic would be generated within the old city by analysing the characteristics of nine of the ten sub-divisions previously made (the tenth being the cathedral close which is not normally a significant traffic generator). We made broad estimates of the number of jobs in each zone, and sub-divided the total generation of work journey movements and ‘essential’ movements in proportion. Similarly, the generation of shopping and other private movements was sub-divided in proportion to estimates of the shopping floor area in each zone. Table 6 shows the estimated peak hour generation allotted to each zone.

Table 6: Peak hour generation in each zone (p.c.u.)

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We assumed that the traffic associated with the nine zones would disperse in six general directions, and that the proportion of all traffic moving in each direction would be much the same as it is now. It was then possible to trace the paths of the various groups of traffic under two sets of conditions, assuming in both cases the existence of the primary network previously described, and the existence of the additional link across the south-east quarter of the old city:

1. That there would be freedom of passage all through the existing streets of the old city, with connections on all sides to the primary network.
2. That the old city would be divided (as far as traffic circulation is concerned) into self-contained units, roughly equivalent to the nine zones previously selected, each unit being independently connected to the network.

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In the first set of conditions (freedom of movement throughout the old city) we made ‘traffic assignments’ to each possible route, taking into account whether people, faced with a free choice, would proceed direct to their destinations via the city streets, or go round the primary network for part of the journey. In practice the choice would be influenced by many considerations, but the main one is duration of journey-time.

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These assignments showed conclusively that if traffic were allowed to filter at will through the area, the demand for road space near the centre would be far in excess (about 50%) of the actual physical capacity of the streets, and many times the ‘environmental capacity’.

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We then investigated the second set of conditions in which the driver has no alternative but to proceed direct to or from the zone of his choice via the primary network. We concluded that it would not be necessary to accept the rigid division into nine zones, but that a minimum of four main groups would suffice, with two main barriers to cross-movement. The first barrier would be on an east-west line roughly along the line of the River Wensum. This would have the advantage, inter alia, of preventing traffic generated in the predominantly industrial area from penetrating into the old street network of the historic city. The location of the second barrier, which would be required on a north-south line, is more difficult to determine because there is no natural line to follow. But a barrier roughly from St. Georges Bridge on the Wensum to Ber Street to the south would allow a reasonably good internal circulation system to be formed out of the existing streets, with fairly evenly balanced loads as far as the primary network is concerned.

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The four main groups and the two barriers are shown in Figure 162. These are illustrations of principles only. In practice much detailed study, accompanied perhaps by full-scale experiments, would be required of traffic behaviour, and of the possible social consequences of the barriers, before final decisions could be taken. It is possible, moreover, that some further breakdown of the four main groups would be required to deal with conditions at certain localities.

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It should perhaps be emphasised that by ‘barriers’ we do mean a physical stopping off of streets to prevent the passage of vehicles (with the possible exception of buses), though not, of course, of pedestrians or cyclists. We do mean literally the closing to traffic of the bridges over the Wensum except towards the west where the barrier would lie south of the industrial area. The concept, in effect, is to convert the old city into four ‘rooms’ each with its ‘doors’ from a new external corridor system, instead of each room being in direct communication with the next through a multitude of doors. If this seems a startling concept we can only observe that a policy somewhat on these lines, with the discipline it will involve for motor traffic, seems to be the only way of saving the old city from a descent into such chaos that eventually an irresistible demand will arise for it to be swept away.