摘要：This paper uses analytical and numerical models to illustrate how the presence of other distortions withinthe transport system changes the overall welfare effect of a congestion tax. These other distortions includea transit fare subsidy, congestion on competing (unpriced) routes, accident externalities, gasoline taxes,and pollution externalities.Each of these pre-existing distortions can substantially alter the welfare effect of a congestion tax thatwould be predicted by a first-best analysis. If congestion taxes encourage travel on other congestedroutes, they can produce sizeable indirect welfare losses. In addition, induced reductions in the demandfor gasoline can lead to substantial welfare losses when, as appears to be the case for European countries,gasoline taxes significantly exceed marginal pollution damages. On the other hand, congestion taxes mayproduce significant welfare gains by offsetting accident externalities, though these gains are partiallyoffset by increased accidents on competing roadways. To the extent that congestion taxes increase thedemand for transit, they can induce significant welfare gains or losses, depending on whether transit faresare above or below marginal supply costs.The importance of other distortions varies considerably across different transport systems and acrossdifferent countries. Our generic analysis illustrates the proportionate change in the welfare effect of acongestion tax due to each of these distortions over a wide range of parameter scenarios.
