Mayor: Periodically an ice cream company will hold a free ice cream day as a promotion  Showing up may not cost you any money, but it sure does cost you time  We learn from this that when something valuable costs no money you get overconsumption and long lines  Currently, those who drive to work complain about the congestion they face in their rush-hour commutes  What is needed is a system for charging people for the use of roads during rush hour
Then rush hour congestion will abate
It is a general claim used in support of the argument's overall conclusion.