Accident costs can be an important element in the cost/benefit assessment of transport policy and, where a policy is likely to result in modal transfer, it is necessary to predict the associated change in the number of accidents by reference to casualty rates disaggregated by mode. The casualty rates per kilometre given here apply to London as a whole and were designed for general application to aggregate predictions. Based on accident data from police records and travel data from the 1978/9 National Travel Survey and the 1981/2 Greater London Transportation Survey, the rates varied from over 1500 Casualties per 1000 million kilometres for motor cyclists down to 75 casualties per 1000 million kilometres for bus passengers. A similar pattern of risk applied to males or females travelling on weekdays or at the weekend and, again, when the rates were translated into money costs: 760 per 100000 kilometres at 1986 prices for motor cyclists on weekdays and 2770 per 100000 kilometres at the weekend, down to 14 per 100000 kilometres for bus passengers. Compared with national values, the casualty rates for London were two to four times higher (depending on the mode) but the average levels of severity were less and this tended to reduce the differences in cost rates. The method is illustrated by applying the cost rates to the changes in travel distance predicted by the TRRL London Area Model, following a doubling of the bus and underground rail fares. This gave an increase in the total cost of accidents (with damage to property and damage-only accidents included) of 31 per cent of the total transfer cost (accident costs plus loss of consumer surplus) or nine per cent of the net loss of social benefit. A 50 per cent increase in car operating costs gave a saving in accident costs almost equal to the loss of consumer surplus (so that the net transfer cost was small) and represented four per cent of the net gain of social benefit.

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