It is widely k n o w n that road transport creates many different kinds of 'externalities', affecting human health, regional and global c l i - mates, congestion, road wear and tear, accidents, noise, soiling and the so-called 'barrier effect'. The a im of this chapter is to present order of magnitudes estimates of these costs for Sweden and to discuss the policy response. Chapter 2 has presented the case that it is the marginal external costs that matter from an efficiency point of view, and yet a comprehensive picture of these costs is almost impossible to give, since these costs vary dramatically i n different circumstances. Therefore, i n addition to some examples of estimated marginal external costs, the total tax-relevant external costs w i l l also be presented since these give an indicat ion of the severity of the problems. These costs are defined as the total amount of tax p a i d that w o u l d occur if the road charge system were designed i n an economically optimal way. Finally, these costs are compared w i t h the actual tax p a i d i n order to see whether road users as a group are 'over-charged' or not.