When it comes to mass transit, politicians never learn. Last month, Nashville Mayor Megan Berry announced a $5.2 billion proposal that involves building 26 miles of light rail and digging an expensive tunnel under the city’s downtown. Voters will be asked in May to approve a half-cent sales tax increase plus additions to hotel, car rental and business excise taxes to pay for the project.

San Antonio’s mayor, Ron Nirenberg, also wants to lay rail, even though his city’s voters blocked light-rail plans in 2000 and 2015. In 1933,...