Chapter III – part two: A large town

Peak hour generation and parking

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Commuters. The area under study contains about 60% of the floor space of the ‘central zone’ defined in connection with the foregoing traffic estimate. We assumed that the employment in the study area and the number of cars used for the work journey would be of the same proportion (60%). The number of persons coming to work by car could therefore be about 16,000 in 11,500 cars, all needing parking space. It is estimated that they would create a peak hour flow, assuming present working hours are maintained, of about 8,000 p.c.u. per hour.*
* p.c.u., or passenger car units, is a measure of the volume of mixed types of vehicles in a traffic stream expressed in terms of the equivalent number of ‘passenger cars’, e.g., 1 bus = 3 p.c.u.

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Shoppers. Out of 67,000 daily shopping journeys into the central area from outside, we assumed that 64%, or 43,000 would eventually be made by car. With an occupancy rate of 1.3, this would result in 33,000 cars. Assuming a parking turnover of 5, then 6,600 spaces would be needed. Assuming 10% of the cars leave during the peak hour, the peak hour flow would be 3,300 p.c.u.

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Essential traffic. We estimated that the total daily generation would eventually amount to 34,500 journeys, of which 11,500 would involve cars and the remainder vans and lorries. Some 2,000 parking spaces would be needed for the cars at a turnover of 6.0, and 3,600 spaces of various kinds for the others at a turnover of 6.5. Assuming 8% of these vehicles leave during the peak hour, the flow would be 3,675 p.c.u.

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Buses. We estimated that approximately 775 buses would be needed at the peak hour to cater for workers and shoppers not using cars. This would be equivalent to an outward flow of 2,325 p.c.u. We allowed in addition an outward flow of 700 p.c.u. during the peak hour for other forms of traffic, such as visitors to public buildings, or places of entertainment.

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Total parking and peak hour generation. The parking spaces required, and the maximum acceptable peak hour generation, are obtained by summation of the above figures. The totals are set out in Tables 4 and 5.

Table 4: Central area parking and loading requirements

Type of traffic	Number of parking spaces	Number of loading bays, and other resting spaces	Total
Commuters	11,500
Shoppers	6,600
Essential cars	2,000
Essential vans and lorries		3,600
Total	20,100	3,600	23,700

Table 5: Central area peak hour generation

	Peak hour generation (p.c.u.)
Type of traffic	Cars	Lorries	Buses	Total
Commuters	8,000			8,000
Shoppers	3,300			3,300
Essential	920			920
Buses			2,325	2,325
Other				700
Total	12,920	2,755	2,323	18,000