This report compiles a large data set of in-use transit bus emissions tests for use in a meta-analysis to define ranges of exhaust emissions for urban bus fuel and technology combinations. The analysis also looks at both local and global emissions to understand their impact on human health and the environment.

Key findings include:

• There is a wide range of emissions values even for the same fuel and technology.
• Many of the factors explored, such as altitude and drive cycle, do have an impact on emissions.
• No single fuel is best in all categories of emissions if the appropriate exhaust after-treatment technologies are used, which means that these technologies are key to reducing emissions.
• The technologies that show the lowest emissions for key pollutants, such as NOx, PM, and CO2 equivalence, are compressed natural gas with a three-way catalyst, 100 percent biodiesel, and ultra-low sulfur diesel with selective catalyst reduction.

Download the report in English here: Exhaust emissions of transit buses

Download the report in Spanish here: Emisiones de escape de autobuses de transporte publico