the social cost of further vehicle-generated pollution will dier as well.
Four main types of external costs have been included in our analysis: accidents; emissions;
noise; and unrecovered costs associated with the provision, operation, and maintenance of public
facilities. In each case we have used conservative values for the various key parameters, so thatour estimates of external costs constitute baseline values. Increasing the values assigned to preventing
a fatality, reducing trac noise, or improving air quality will lead to concomitantly
higher external cost ®gures.