A more complex MOE used for both traditional capacity-related transportation improvements and TSMO projects is emission levels. The emissions categories typically include hydrocarbons (HC)/reactive organic gases (ROG), nitrogen oxide (NOx), carbon monoxide (CO), carbon dioxide (CO2), particulate matter (PM10) or fine particulate matter (PM2.5), and sulfur dioxide (SO2). Most emissions estimates are based on the application of an emissions rate per VMT. However, emissions rates are sensitive to a variety of variables, such as vehicle speeds and type of vehicle.