According to the U.S. Census Bureau, nearly 90 percent of the 4.5 million workers in the Los Angeles area spend an average of 60 minutes each day commuting on a roadway or railway. When USC researchers from the Viterbi School of Engineering set out to study the environmental benefits of different modes of public transit in LA, they found some unexpected results: certain SoCal public transit routes that were entirely underground exposed passengers to greater concentrations of carcinogens in the air. The research was published in Aerosol and Air Quality Research on November 29, 2017.