Reducing emissions from diesel engines is one of the most important public health challenges facing the country. Despite the EPA’s stringent diesel engine and fuel standards taking effect over the next decade, the 20 million engines already in use will continue to emit large amounts of nitrogen oxide and particulate matter, both of which will contribute to serious public health problems for years to come. Fortunately, a variety of cost-effective technologies can dramatically reduce harmful emissions, save fuel, and help our nation meet its clean air and sustainability goals. This book analyzes the cost-effectiveness of various diesel emission reduction strategies, wherein the EPA compares the amount of federal grant funds used, to the lifetime tons reduced, to evaluate the effectiveness of federal investments in spurring diesel emission reductions.