Appendix 2: Cost-benefit analysis and accessibility and environment

Environment

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When vehicles are admitted into an area, environmental conditions are altered. Accessibility for vehicle-users may be improved, but the environmental standards lowered. There are many difficulties in assessing the effect of such changes on environment: what aspects to take account of, how to overcome the absence of established methods of measurement and the lack of specific environmental standards. These are questions for which there are as yet no fully satisfactory answers, so that precision and objectivity in assessing environmental conditions are not yet possible.

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To allow some comparison to be made of the environments of the various Newbury schemes, a second ‘check list’ has been constructed. It follows the lines, but not the content, of the (A) list used as part of the measure of Accessibility. It takes into account the safety, comfort, convenience, and appearance of an area when considered from the point of view of the people living there, working or walking about. These aspects are allotted maximum possible scores which are weighted on the basis of value judgments-for example, it is assumed that safety is more necessary to the occupants of an area than are any of the other factors included in the list. The maximum possible total score for any area is 100.

Check-list for adequacy of the Environment (E)

Items	Aspects taken into account (Broad Performance Standards)	Maximum possible score
Safety	1. Full separation of pedestrians and vehicles 2. No intrusion of through traffic or traffic of unsuitable character 3. No major conflict points; no excessive speeds	28 16 16
		60
Comfort	1. No undue proximity of pedestrian areas or buildings to medium-heavy vehicle flows 2. Ditto to grouped car parks or structures, e.g. garages, overpasses, etc. 3. No overpowering ‘scale effect’	7 5 3
		15
Convenience	1. No severance of closely linked uses by traffic routes (distributors) or unsuitable traffic flows 2. Adequacy of pedestrian access system within the area and to other areas 3. Adequacy of access to public transport for pedestrians	5 5 3
		15
Appearance	1. No dominance of scene by moving or parked vehicles 2. Ditto by structures for vehicles, e.g. garages, overpasses, etc. 3. Ditto by street furniture or traffic management devices	4 4 2
		10
	Maximum possible total score	100

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Both the (A) and the (E) lists consist of broad descriptions of desirable conditions. But in the absence of detailed standards and effective units of measurement, these broad descriptions themselves necessarily lack precision; and the testing of schemes against each item can at present be carried out only on a subjective basis. The values of (E) for the Newbury schemes were assessed on the basis of the above check list. The results are shown in Table 4, which indicates that the environmental score, as measured by (E), would increase from 38 under present conditions to 79.

Table 4: The environment of the Newbury schemes

	Present layout	Scheme A	Scheme B	Scheme C
Crude capacity (v.p.h.)	1,600	1,700	3,500	3,500
(E) score	38	64	72	79
Environmental Capacity	610	1,090	2,500	2,760
Total site area (acres)	113	124	132	132
Index of Environmental Capacity (per acre of site)	5.4	8.8	19.2	21.9

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The (E) score gives no indication of the capacity of an area to admit vehicles without detriment to the environment. For example, two quite differently arranged areas might each have an (E) score of 80, even though one might allow many more vehicles into it than the other. For this reason we have made use of the concept of Environmental Capacity (Chapter II, paras 129-132), and defined it as:

Environmental Capacity = Crude Capacity × B / 100

A high figure for Environmental Capacity may be brought about either by a high Crude Capacity or by a high (E) score, or both. Environmental Capacity is intended to indicate the ability of an area to admit vehicles without detriment to the environment. But since there is clearly no simple, linear relationship between safety, noise or convenience and the number of vehicles, environmental capacity does not measure the actual number of vehicles that could be accepted into the area. Environmental capacity should therefore be regarded as an index of capacity.

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Environmental Capacity cannot be used in the above form to compare alternative schemes of different sizes; for that reason it is expressed in Table 4 as a capacity per acre of site. The Table shows a progressive increase in Environmental Capacity per acre of site for Schemes A, B, and C. This increase in capacity is due to the combined effect of the higher Crude Capacities and higher (E) scores for Schemes B and C.

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The quality of the different schemes can now be compared.
If reference is made to Tables 3 and 4, the following points emerge:

1. The fairly high Accessibility for present conditions is partly explained by the good penetration that vehicles can achieve at the expense of environment. It is also explained by the comparatively low level of potential generation at present.
2. If no works are carried out, the Environmental Capacity of course remains constant, but Accessibility falls sharply, because of the greater potential traffic generation.
3. Scheme A would raise Environmental Capacity to a figure higher than exists at present, but Accessibility would remain below its present level.
4. Schemes B and C would have considerably higher Environmental Capacities and Accessibility than obtain at present. The C scheme has an Accessibility Index I 3 times that for present conditions but its Index of Environmental Capacity is about 4 times that for present conditions.