The EPA first began setting emission standards for motor vehicles in the late 1960’s. Since that time, the standards have changed multiple times, becoming more and more strict as technology advanced and policymakers gained a greater understanding of the impact of vehicular emissions on the environment and human health. Emission standards are developed separately for different types of vehicles and can generally be organized into three different areas: light- and medium-duty vehicles, heavy-duty vehicles, and heavy-duty nonroad equipment (such as locomotives and construction equipment). This page discusses the standards currently used by the Environmental Protection Agency (EPA) for vehicles which are registered for on-road use.
Please note that some states have adopted emission standards set in place by the California Air Resources Board (CARB), including California and several northeastern states. As Texas uses the emission standards set in place by EPA, this information is limited to a discussion of these standards. For more information on the California emission standards, see CARB.