Source Category

Status (Date Promulgated; Effective Date)

Marine engines

New recreational engines required to meet new standards with 55–80% reduction in emissions (depending on pollutant) (2002; 2006–2009)

Largest maritime commerce engines regulated to international standards for NOx (not PM) (2003; 2004)

Smaller maritime commerce engines regulated for NOx, PM (1999)


Initial standards for smoke only; new standards adopting International Civil Aviation

Organization rules requiring 20% reduction in NOx emissions (1997; full effect in 1999)


Regulations applying to new locomotive engines and to remanufactured engines from 1973 and later locomotives; ultimately (2040) expected to reduce NOx by 60%; PM by 46% (1997; Tier 0 for engines 1973–2001; Tier 1 for engines 2002–2004; Tier 2 for engines 2005 and later)

(HDVs), and motorcycles that are used for transportation on the road. On-road vehicles may be fueled with gasoline, diesel fuel, or alternative fuels, such as alcohol or natural gas. Nonroad sources refer to gasoline- and diesel-powered equipment and vehicles operated off-road, ranging in size from small engines used in lawn and garden equipment to locomotive engines and aircraft.

In principle, the mobile-source emissions can be controlled with three types of strategies:

  • New-source certification programs that specify emission standards applicable to new vehicles and motors.

  • In-use technological measures and controls, including specifications on fuel properties; vehicle inspection and maintenance programs; and retrofits to existing vehicles.

  • Nontechnological (for example, behavior modification) measures to control usage or activity (for example, via management of transportation).

This chapter summarizes how each of those strategies is used in the United States and concludes with a critical discussion.

The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement