Last Thursday, Maryland Governor Larry Hogan unveiled a $9 billion project to widen three of the state’s most heavily trafficked highways: I-270, I-495—also known as the Capital Beltway—and MD-295, the Baltimore-Washington Parkway. What the governor’s office dubbed the Traffic Relief Plan involves constructing two express toll lanes each way—or four total toll lanes—to all three highways. Widening the Capital Beltway and the section of I-270 connecting the growing commuter-city of Frederick to Washington, D.C., would cost an estimated $7.6 billion, which the state expects to be financed via public-private partnerships: Private companies would build and maintain the new toll lanes,...