As The Washington Post reports, Oregon and Utah already have some form of mileage tax, but there are several reasons the idea has yet to take off. First of all, there are privacy concerns, since some level of data collection would be required. Additionally, some argue moving away from a gas tax could disincentivize buying fuel-efficient vehicles. Also, a mileage tax would arguably unfairly tax people who can’t afford to live in expensive cities but drive long commutes to reach jobs in metropolitan areas. Buttigieg’s comments drew criticism from both sides of the aisle on that front.