This rulemaking revises the tailpipe emission portions of the Federal Test Procedure (FTP) for light-duty vehicles (LDVs) and light- duty trucks (LDTs). The primary new element of the rulemaking is a Supplemental Federal Test Procedure (SFTP) designed to address shortcomings with the current FTP in the representation of aggressive (high speed and/or high acceleration) driving behavior, rapid speed fluctuations, driving behavior following startup, and use of air conditioning. An element of the rulemaking that also affects the preexisting ``conventional'' FTP is a new set of requirements designed to more accurately reflect real road forces on the test dynamometer. The Agency is also finalizing new emissions standards for the new control areas with a specified phase-in period for these standards. These regulations are expected to reduce emissions from LDVs and LDTs by two percent for non-methane hydrocarbons (NMHC), 11 percent for carbon monoxide (CO), and nine percent for oxides of nitrogen (NO<INF>X).