Road pricing can potentially provide positive environmental results, although specific environmental results may be mixed. Congestion reduction effects do lower some pollutants by decreasing or eliminating stop and go driving in heavy traffic, Put faster travel can also increase emissions of other pollutants.
Recent research that examined the effects of road pricing on a broad range of pollutants found that encouraging reduced vehicle travel and modal shifts would lead to a net reduction in emissions of all the pollutants examined.46 In addition, by shifting more of the costs of driving to marginal costs and away from fixed costs (e.g., car registration fees, flat insurance rates only loosely related to miles driven, etc.), drivers would drive somewhat less, yielding environmental benefits. However, if comprehensive road pricing were not supplemented by some kind of charge on carbon emissions (such as a carbon tax), there would be some offsetting impacts because it would then become relatively cheaper to drive lower-mileage vehicles (since gasoline consumption would no longer be taxed).