42 U.S. Code § 16102. Diesel fueled vehicles

(a) Definition of tier 2 emission standards

In this section, the term “tier 2 emission standards” means the motor vehicle emission standards that apply to passenger cars, light trucks, and larger passenger vehicles manufactured after the 2003 model year, as issued on February 10, 2000, by the Administrator of the Environmental Protection Agency under sections 7521 and 7545 of this title.

(b) Diesel combustion and after-treatment technologies

The Secretary shall accelerate efforts to improve diesel combustion and after-treatment technologies for use in diesel fueled motor vehicles.

(c) GoalsThe Secretary shall carry out subsection (b) with a view toward achieving the following goals:
(1) Developing and demonstrating diesel technologies that, not later than 2010, meet the following standards:
The heavy-duty emissions standards of 2007 that are applicable to heavy-duty vehicles under regulations issued by the Administrator of the Environmental Protection Agency as of August 8, 2005.
Developing the next generation of low-emission, high efficiency diesel engine technologies, including homogeneous charge compression ignition technology.