Emissions Analysis of Southern California Metrolink Commuter Rail

The Southern California Regional Rail Authority began constructing a new commuter rail system called Metrolink in October 1992. When complete, the Metrolink system will form the nation's sixth largest commuter rail system and is expected to alleviate congestion and help obtain better air quality. To estimate the air quality impact, emissions of CO, HC, NO_x, and PM associated with an automobile-only–based commute and a Metrolink-based commute from Riverside to Los Angeles are compared. Analysis of the Metrolink-based commuting scenario includes the emissions from the home-to-station automobile trip and the Metrolink diesel locomotive emissions. Essential data for the automobile emissions modeling process were obtained through a survey of Metrolink passengers and through remote emissions sensing of Metrolink passenger vehicles. Train emissions were estimated using emission rate data provided by recent diesel locomotive studies. Results indicated that at current ridership levels there is a reduction in total amount of all four pollutants combined through Metrolink commuting. On a pollutant-by-pollutant basis, it was estimated that the Metrolink commuting scenario reduces the emissions of CO and HC relative to the automobile-only commuting scenario; however, it increases the emissions of NO_x and PM. The minimum amount of Metrolink ridership required to get a net emissions reduction from the system is predicted.