Under the Clean Air Act, EPA is responsible for setting National Ambient Air Quality Standards for certain pollutants considered harmful to public health and the environment. EPA has set these standards for six such pollutants, known as criteria air pollutants: carbon monoxide, nitrogen oxides, sulfur oxides, particulate matter, ozone, and lead. Diesel exhaust contains nitrogen oxides, particulate matter, and numerous other harmful chemicals. Exposure to nitrogen oxides can result in adverse respiratory effects, and nitrogen oxides contribute to the formation of ozone, which can cause respiratory illnesses, decreased lung function, and premature death. A large body of scientific evidence links exposure to particulate matter to serious health problems, including asthma, chronic bronchitis, heart attack, and premature death. Nondiesel mobile sources, industrial processes, and power plants, among other sources, generated the remaining nitrogen oxide emissions; fossil fuel combustion, dust, and agricultural activities, among other sources, generated the remaining particulate matter emissions. 43 percent and 42 percent of such emissions, respectively, from diesel engines. EPA has progressively implemented more stringent diesel emissions standards to lower the amount of key pollutants from mobile diesel sources since 1984. For example, EPA regulations for heavy-duty highway diesel engines required a 98 percent reduction from 1988 allowable levels of nitrogen oxide and particulate matter emissions for new engines built after 2009. The most recent emissions standards for construction and agricultural equipment began to take effect in 2008 and required a 95 percent reduction in nitrogen oxides and a 90 percent reduction in particulate matter from previous standards, which took effect in 2006 and 2007. In 2008, EPA issued its most recent regulations for new marine vessels and locomotives, which EPA expects will, by 2030, reduce nitrogen oxide emissions from the engines of these sources by about 80 percent and particulate matter emissions by about 90 percent compared to previous standards. Figures 1 and 2 show the effective dates of major reductions in allowable amounts of nitrogen oxide and particulate matter emissions from mobile diesel sources. Owners and operators of diesel engines can undertake a variety of activities to reduce diesel emissions, including retrofitting, rebuilding, or replacing existing diesel engines or vehicles; installing devices that reduce idling of diesel engines; and converting diesel engines and vehicles to use cleaner fuels. Retrofitting existing diesel engines generally involves the installation of emissions control devices, such as filters, on a vehicle’s tailpipe. Rebuilding components of existing diesel engines can return engines to their original emissions levels or involve the installation of new technology that produces lower levels of emissions. Replacing existing diesel engines and vehicles with newer, lower emitting engines or vehicles can lead to significant emissions reductions, but because it is a costly option, it may be most appropriate for the oldest, most polluting vehicles. Devices that reduce idling of diesel engines generally allow a vehicle’s heat, air conditioning, and other electrical equipment to run without operation of the vehicle’s main engine. Converting diesel vehicles and engines to use cleaner fuels can also provide significant emissions reductions. The Government Performance and Results Act, as amended, requires agencies to prepare annual performance plans that contain, among other things, a set of annual goals that establish the agencies’ intended performance and measures that can be used to assess progress toward achieving those goals. DOE, DOT, and EPA establish and organize these goals and performance measures at differing agency and administrative levels. Specifically, DOE and EPA establish strategic goals and performance measures for each goal as part of their agencywide performance plans. DOT establishes strategic goals as part of its agencywide strategic plan, but the agency’s administrations—the Federal Aviation Administration, Federal Highway Administration, and Federal Transit Administration, among others—generally establish their own performance measures for assessing their programs’ contributions to the department’s strategic goals. Federal grant and loan funding for activities that reduce mobile source diesel emissions is fragmented across 14 programs at DOE, DOT, and EPA. Many of these programs generally target air pollution, but of the 14 programs, one—EPA’s Diesel Emissions Reduction Act program—has a specific purpose of reducing mobile source diesel emissions. The remaining 13 programs focus on other goals or purposes, such as supporting energy efficiency projects or reducing petroleum use. Nevertheless, each of these programs allows or requires a portion of its funding to support activities that have the effect of reducing mobile source diesel emissions. For example, authorizing legislation for DOT’s Congestion Mitigation and Air Quality Improvement program directs grant recipients to give priority to certain activities, including retrofitting diesel engines and vehicles. The 14 programs provide funding through one or more mechanisms, including competitive grants, formula grants, and loans. Specifically, 13 of the programs provide funding through competitive and formula grants, and 1 program—DOT’s State Infrastructure Banks program—provides loans.gaps in the programs, such as mobile sources that are not eligible for funding. See appendix II for additional information about each program. We did not identify any From fiscal years 2007 through 2011, these 14 programs obligated at least $1.4 billion for activities that have the effect of reducing mobile source diesel emissions. According to data from DOE, DOT, and EPA, the American Recovery and Reinvestment Act of 2009 provided about $870 million of this funding. The $1.4 billion amount is a lower bound because DOT could not determine the amount of grant and loan funding some of its programs have provided for projects that reduce mobile source diesel emissions. According to DOT officials, the agency does not track this information because statutory program requirements do not call for the agency to do so. These activities that have the effect of reducing mobile source diesel emissions include replacing fleets of older diesel trucks or school buses with natural gas vehicles, installing particulate matter filters on construction equipment, and replacing diesel-powered airport luggage transporters with electric vehicles. As table 1 shows, some of the programs that support these activities have broad purposes, such as increasing energy efficiency in transportation, reducing petroleum consumption, or funding public transportation projects, and other programs have narrower purposes, such as reducing emissions at airports, constructing ferry boats and related facilities, or promoting alternative transportation systems in and around national parks. As table 2 shows, each of the 14 relevant programs overlaps with at least one other program in the specific types of activities they fund, the program goals, or the eligible recipients of funding. For example, 6 of the 14 programs share a broad goal of increasing energy efficiency, and local governments are eligible to receive grants under 10 of the programs. In addition, we found that 13 of the 14 programs fund activities that retrofit diesel engines or vehicles, and 11 programs fund activities that reduce diesel vehicle idling. We also identified the potential for overlap among these 11 programs and an excise tax exemption for certain vehicle idling reduction devices because the tax expenditure and the 11 programs all provide incentives to use idle reduction devices to reduce diesel emissions. Appendix III provides additional information on this and two other tax expenditures related to diesel emissions reductions. We also identified several instances of duplication where more than one program provided funding to the same recipient for the same type of activities. In one case, a state transportation agency received $5.4 million from DOT’s Transit Investments in Greenhouse Gas Emissions Reduction program to, among other things, upgrade 37 diesel buses to hybrid diesel-electric buses; $3.5 million from DOT’s Congestion Mitigation and Air Quality Improvement program to replace diesel buses with 4 hybrid diesel-electric buses; and $2.3 million from DOT’s Clean Fuels Grant program to replace 4 diesel buses with hybrid electric buses. In another case, a nonprofit organization received $1.1 million from EPA’s Diesel Emissions Reduction Act Program to install emission reduction and idle reduction technologies on 1,700 trucks as well as $5.6 million from a state infrastructure bank established under DOT’s program to equip trucks and truck fleets with emissions control and idle reduction devices. Even with duplication among the programs, several factors make it difficult to precisely determine whether unnecessary duplication exists. First, when different programs fund the same diesel emissions reduction activities, it is not necessarily wasteful. For example, a transit agency could use funds from two different programs to replace two separate fleets of aging diesel buses. Second, grant recipients may leverage funding from more than one program to support the full cost of diesel emissions reduction projects. In some cases, grant recipients have used funding from multiple agencies, in addition to local matching funds, to support the cost of large projects that include multiple diesel emissions reduction activities. Third, agencies were often unable to provide information necessary to determine whether and to what extent unnecessary duplication exists among the programs. For example, several agencies reported that they do not track costs for administrative functions at the program level. Without information on these costs, it is difficult to determine whether and to what extent programs perform duplicative administrative functions that could be consolidated to provide grants and loans more efficiently. The fragmentation, overlap, and duplication among these programs result, in part, from their legislative creation as separate programs with different purposes that fund a wide range of activities, some of which have the effect of reducing mobile source diesel emissions. We have previously reported that, as the federal government has responded over time to new needs and problems, many agencies have been given responsibilities for addressing the same or similar national issues. Some of this shared responsibility was intended to recognize that addressing some issues from a national perspective would necessarily involve more than one agency or approach. However, the resulting fragmentation, overlap, and duplication may waste administrative resources and create an environment in which participants are not served as efficiently and effectively as possible. In addition, we have previously reported that fragmentation, overlap, and duplication suggest the need for further examination of programs to identify potential areas for improvement, realignment, consolidation, or elimination. The effectiveness of federal funding for activities that reduce mobile source diesel emissions is unknown because agencies vary in the extent to which they have established performance measures. In addition, few programs collect performance information on their diesel emissions reduction activities because 13 of the 14 programs that fund these activities have purposes other than reducing diesel emissions.