The external costs of transport have been the subject of extensive research. Early gross estimates (Quinet, 1989) suggested congestion costs to account on average for 8.5% of the GDP and from 2.0 to 2.5% for safety. Recent estimates in Europe suggest that annual costs amount to a figure between 32 and 56 billion ECU (EU 1996). Cooper et al (1998) estimate
the costs in Britain at 7 billion ECU, or twice the amount collected by vehicle taxation.