There are no corridors in the United States in which transit carries a significant share of travel that are not downtown corridors. This experience includes Dallas-Fort Worth, New York and most other metropolitan centers. This occurs because it is only to downtown destinations that transit is able to provide the quick, no-transfer express service that can compete with automobile trips. People are not going to switch to transit if it means transferring and thus much longer travel times. The point is that light rail has been demonstrated to be incapable of materially reducing traffic volumes in downtown oriented corridors.
Light rail has even less potential in non-downtown oriented corridors.
Because it does not reduce traffic congestion, it also has little, if any impact on air pollution. I know that there has been much publicity about the perceived development impacts of DART light rail. But development is a complex issue, and the DART reports greatly oversimplify the situation. Dallas-Fort Worth is the fastest growing of the nation's top ten metropolitan areas. That means that development is occurring at a rapid pace.