They just never learn:
Some years ago, Anthony Downs elaborated and popularized the idea with his "Law of Peak Hour Congestion." Here is a nice summary. Without pricing, extra road capacity will simply attract traffic from other sources (other modes, other routes, other times of day, new trips, etc.). Congestion will not be "solved." The idea is simple -- and the lesson has been ignored a thousand times. Officials are loathe to price but love building things. This is "bi-partisan". Crony capitalism is non-denominational.