Art Carden: Heavy traffic is a problem every economist in the world knows how to solve: price road access, and charge high prices during rush hour. With technologies like E-ZPass and mobile apps, it’s easier than ever. That we don’t pick this low-hanging fruit is a pretty serious indictment of public policy. If we can’t address what is literally a principles-level textbook example of a negative spillover with a fairly easy fix, what hope do we have for effective public policy on other margins? (