Washington, D.C. is the nation’s capital — and its suburbs could be moving towards becoming the nation’s capital of privately owned express toll lanes. The Virginia side of the Potomac has placed a big bet on such roadways, with 14 miles of pay lanes in the middle of the region’s famous Beltway, reversible toll lanes along 29 miles of I-95, and construction under way on three more highway segments. Last September, Maryland Governor Larry Hogan announced an even more ambitious plan for his side of the river, covering 77 miles of the Beltway and I-270. If these plans go forward,...