Regulatory Background on the U.S. Mobile Source Emission Control Program

The Clean Air Act

Concern about automobile pollutants dates back to the mid-1950s, when the U.S. Congress first funded research on automobile air pollution control. Then in the 1960s, Congress enacted a federal program authorizing the Secretary of Health, Education and Welfare to establish motor vehicle standards to reduce tailpipe emissions. Congress, dissatisfied with the lack of progress, seized the initiative and specified not only emission limits, but also deadlines for meeting the standards, and an enforcement program to ensure compliance. These changes became a major part of the Clean Air Act Amendments of 1970.

In this 1970 law Congress estimated the magnitude of emissions reductions for automobiles that would be necessary to achieve healthy air quality. For cars, the Act required a 90-percent reduction in hydrocarbons (HC) and carbon monoxide (CO) emissions over 1970 vehicle levels by the 1975 model year and a 90-percent reduction of nitrogen oxides (NOx) over 1971 vehicle levels by the 1976 model year. The Clean Air Act also gave EPA the authority to set standards for trucks and buses and to regulate additional pollutants. In addition, Congress established the framework for an integrated compliance program to ensure vehicles met those standards at the design stage, at the point of production, and in actual use.

Lawmakers recognized that the technology needed to meet the standards did not yet exist and the schedule for compliance was ambitious. But most agreed that the only way to motivate automobile industry to develop the necessary technology was to create the incentive to force such development - thus the concept of technology-forcing standards was born.

The auto companies were not always willing participants in this grand experiment of "technology-forcing" standards, but they and their suppliers rose to the task and began developing the needed technology. By the mid-1970s substantial progress had been made; auto pollutants had been reduced and interim emissions standards met. But the final, congressionally-mandated standards were delayed by both congressional and administrative action. In 1977, Congress amended the Clean Air Act and finally drew the bottom line: gasoline-powered automobiles would be required to meet the stringent HC standard by the 1980 model year, a slightly relaxed NOx standard by 1981, and the CO standard by 1983.

In 1990, Congress again strengthened the motor vehicle program. The 1990 Clean Air Act Amendments established tighter standards for automobiles, trucks, and buses, called for the control of nonroad engines, strengthened EPA's in-use compliance, and established requirements for both conventional and alternative fuels.

Now over 30 years old, the Mobile Source Emission Control Program is generally regarded as a resounding success; it has become a model for other countries that are seeking to address motor vehicle related pollution problems. The nation's air is cleaner now than at any time during the previous three decades. Moreover, the program is extremely popular with the public. Opinion polls have repeatedly shown that Americans want pollution from cars, trucks and buses to be controlled, and that they are willing to pay the price of that control.