Older diesel locomotives may have higher per passenger mile emission rates of NOx and PM compared to other transport modes. Therefore, to reduce human exposure to train-generated air pollution, measures to reduce emissions from existing locomotives are desirable. Fuel use and emission rates (FUER) depend on exhaust after-treatment technology, locomotive operation, and fuels. Variation in locomotive operation results in spatial variation of FUER along the route. Thus, there could be hotspot locations with high emissions. Switching fuels to biodiesel blends affects FUER due to differences in fuel physical and chemical properties. Here, interactions between technology, operation, and fuels were evaluated. Rail yard (RY) and over-the-rail (OTR) measurements were conducted using portable emission measurement system (PEMS) to quantify FUER. Data from multiple measurements were time-aligned and screened for errors. RY measurements included three replicates of a predefined test schedule. OTR measurements included 6 one-way trips on the Piedmont rail route between Raleigh, NC and Charlotte, NC. The retrofit of a selective catalytic reduction-based Blended exhaust After Treatment System (BATS) for controlling NOx emissions was evaluated based on RY measurements. Simultaneously, PEMS-based emission rates were benchmarked to a Federal equivalent method (FEM). The effect of operation was assessed by comparing one-way trips with the highest and lowest trip total fuel use and emissions. Spatial variability in FUER was compared to spatial variability in train speed, acceleration, rail-grade and rail curves. In prior work, FUER were quantified for several blends of biodiesel and diesel. Less than 1 % of the data were excluded during screening. PEMS-based emission rates of CO2, NOx and PM were highly correlated with the FEM. BATS is highly recommended for reducing NOx emissions. Efficient locomotive operation including fewer notch changes and avoiding rapid accelerations and decelerations is recommended for reducing trip total fuel use and emissions. A 20 percent blend of biodiesel in diesel is effective in reducing CO, HC and PM emission rates. A combination of technology, operation and fuels is highly recommended to simultaneously reduce fuel use and emissions of CO, HC, NOx and PM. This research demonstrates that PEMS-based measurements are reliable for quantifying the effect of technology, operation and fuels on FUER.
