TDM tends to provide modest, but multiple benefits. Conventional transportation planning tends to undervalue TDM by focusing on just one or two objectives at a time. Transportation markets often violate these principles in ways that increase encourage excessive automobile use, as summarized in the table below. Market Requirements Common Transport Market Distortion Consumer choice. Consumers should have viable choices.
Consumers often have few viable alternatives to automobile travel.
Producers should face competition to encourage innovation and efficient pricing. Most roads and transit service is provided by public monopolies. There is often little competition or incentive for innovation. Consumers should bear the costs they impose. Transportation planning practices, zoning codes, and tax policies tend to favor automobile travel.