Status of the Nation’s Highways, Bridges, and Transit:
2002 Conditions and Performance Report
Part I: Description of Current System
Part II: Investment Performance Analyses
Part III: Bridges
Part IV: Special Topics
Part V: Supplemental Analyses of System Components
While the Clean Air Act has controlled pollutant emissions from all air pollution sources, the greatest success can be found in the control of on-road mobile sources. Emissions reductions from motor vehicles have accounted for 84 percent of the total emissions reductions of the six criteria pollutants since 1970.
Air pollutant levels nationally have improved considerably, and although some areas have shown increases, concentration levels in most urban areas, where problems have historically been the most severe, have shown marked
improvement in response to stringent controls.
Since 1970, population has increased 38 percent; the number of people employed has increased 68 percent; the Gross Domestic Product has increased 147 percent; the number of drivers has increased 68 percent; and total vehicle miles traveled (VMT) per year have increased 142 percent. Despite these challenges, national on-road motor vehicle emissions have declined 77 percent.
Increasingly tight EPA engine and fuel standards for both cars and trucks have been instrumental in decreasing emissions, and will continue to do so. Emissions reductions have also been the focus of other programs, such as the Congestion Mitigation and Air Quality Improvement Program, which authorized over $8 billion in TEA-21 for transportation projects aimed at reducing emissions.
Transit vehicles account for a very small percentage of total vehicle emissions,
less than one percent of the total. Transit operators, however, are still
making strides in improving emissions from transit vehicles through the
introduction of clean-burning, more fuel-efficient buses. Since 1992,
the share of alternative fuel buses in the transit fleet increased from
1.2 percent in 1992 to 7.5 percent in 2000. Alternative fuel transit buses
currently operate in 39 States.
Reducing pollutant emissions from motor vehicles has been the major factor to this trend in cleaner air, while enhancing the community and social benefits of transportation. Technological innovations, cleaner fuels, and targeted highway and transit programs have reduced emissions significantly over the past 30 years, and this trend is projected to continue well into the future.