All this week we've been exploring the debate around a plan to stem congestion on U.S. 280 in Jefferson and Shelby Counties. The proposal from the Alabama Department of Transportation would add elevated lanes to a portion of the route. It would also add tolls to four lanes. But how effective would tolling be? WBHM's Andrew Yeager spoke with Richard Arnott, an urban economist at the University of California, Riverside. Arnott says tolls are one strategy cities use to control congestion. But toll roads are less common within a metropolitan area.