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and the vehicle concentration. It is important to bear in mind that
the problems are essentially localised, since the concentration of
pollutants rapidly diminishes as distance from the source increases.
Vehicles may emit literally hundreds of different complex compounds, and
therefore a vigilant attitude must be preserved, and engines would have
to conform to arbitrary control values. There would be continual attempts
to establish what effect these controls would have, and what additional
cost of modifications to existing engines, or of the development and
production of new types, could be tolerated. Objection to degrees of
visible smoke can be established from subjective assessments by groups of
people, but the same method cannot be applied to gases which may be toxic,
or which may cause harm to develop slowly.
It is clear that the aims for the highest possible efficiency of
operation, and for the lowest possible cost of a power unit which will
perform a given task must now be sacrificed. While the term "cost
effectiveness" has become more widely quoted since legislation of various
forms has enveloped motor vehicles, it must be an almost impossible quantity
to evaluate, when attempting to weigh up commercial or economic viability
against an indeterminate effect of pollution on human, animal and plant
life, and the environment.
I have submitted a survey of the literature on this subject to
the appropriate Committee of the Society of Community Medicine, who will
be considering what further action on public health grounds is possible to
hasten the abatement of this increasing nuisance.

/OTHER
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