Optimal Policy Instruments for Externality-Producing Durable Goods Under Time Inconsistency

When consumers exhibit present bias and are time-inconsistent, the standard solution to market failures caused by externalities--Pigouvian pricing--is suboptimal. I investigate policies aimed at externalities for time-inconsistent consumers. Welfare-maximizing policy in this case includes an instrument to correct the externality and an instrument to correct the present bias. Either instrument can be an incentive-based policy or a command-and-control policy. Calibrated to the US automobile market, simulation results from a model with time-inconsistent consumers suggest that the second-best gasoline tax is 18%-30% higher than marginal external damages. These simulations also suggest that social welfare is maximized with a gasoline tax set about equal to marginal external damages and a fuel economy tax that increases the price of an average non-hybrid car by about $750-$2200 relative to the price of an average hybrid car.