Chapter 3 – Part four: A central metropolitan block

Densities

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We then had to decide the densities of the re-instated uses. Working to London County Council standards, we assumed an average residential density of 200 persons per net acre for the 7,000 permanent residents (the remaining 2,000 of the total population being in hotels and hospitals), a minimum open space provision of 075 acres per 1,000 permanent residents, a plot ratio of so for Oxford Street shopping and 35 for all other non-residential uses. We also assumed that a 2-acre primary school site would be required. On the basis of these standards, 34 acres or 23% of the total site area, would be left for roads, loading and parking. This seemed very little, and gave us a warning that when road, parking and loading requirements were worked out in detail, it would probably be necessary to make more space available by one or both of two methods:

1. by raising plot ratios but keeping overall floor areas constant-in effect by reducing the amount of land covered by buildings, or
2. by creating more space through the introduction of additional physical levels for vehicles or pedestrians.

In these calculations we assumed that half the commercial use would be underground storage which in accordance with convention was excluded

Table 10: Estimation of essential and optional traffic

All traffic
Maximum permissible peak hour generation	12,200 p.c.u. per hour (1)
Essential traffic
Total future daily generation of essential journeys (round trips taken at 2 ⅔ times the present level)	36,000
Peak hour generation of essential journeys (assuming 8% of total journeys occur at peak hour)	2,900
Peak hour generation expressed in p.c.. (assuming one-third of vehicles are medium and heavy)	3,800 p.c u. (2)
Parking spaces required for cars used for essential purposes (assuming 12,000 car trips daily with turnover of 6)	2,000 spaces
Loading bays and parking space for other commercial vehicles (assuming 24,000 trips daily and turnover of 6.5)	3,700 spaces
Public service vehicles
Equivalent peak hour load created by P.S.V.s (assuming, pro tem, that 150 buses leave the area during the peak hour)	450 p.c.u per hour (3)
Optional traffic
Balance of peak hour generation available for all optional traffic, i.e. 1 - (2 + 3)	7,950 p.c u. per hour (4)
Allowance for trips other than those connected with work or shopping	750 p.c.u. per hour (5)
Shopping traffic
Estimated total number of daily trips by all forms of travel	115,000
Number of trips made by car at 20% of total	23,000
Number of cars used at occupancy rate of 1.5 persons car	15,500
Number of parking spaces required at turnover of 3.5	4,440
Equivalent peak hour load (assuming 14% of outward trips at peak hours)	2,200 p.c.u. per hour (6)
Work journey traffic
Balance of optional peak hour generation available for work journeys, i.e. 4 —(5 + 6)	5,000 p.c.u. i.e. 4 - (5 + 6)
Number of cars used for work journeys (assuming two thirds of workers leave during peak hour)	7,500
Equivalent number of workers travelling by car (assuming occupancy rate of 1°3 persons/car)	10,000
Total number of workers in area	50,000
Percentage of workers travelling by car	20%