There are a number of options available for reducing the environmental impact of urban bus fleets (or other heavy-duty diesel vehicle fleets). Some steps are relatively simple, while others are more complicated and require some investment and expertise. However, in every country that has been studied, the monetized health benefits of cleaner air have greatly exceeded the implementation costs of reducing vehicle pollution — using some of the steps suggested here. For example, in the United States, recent U.S. EPA regulatory programs aimed at reducing the exhaust emissions from new light-duty vehicles, new heavy-duty diesel trucks and buses, and off-road diesel engines have been estimated to provide approximately $16 of monetized health benefits for each $1 in implementation costs.