Air Pollution:

Reliability of EPA's Mobile Source Emission Model Could Be Improved

RCED-90-138: Published: May 14, 1990. Publicly Released: Jun 18, 1990.

Additional Materials:


Office of Public Affairs
(202) 512-4800

Pursuant to a congressional request, GAO examined the: (1) reliability of the Environmental Protection Agency's (EPA) mobile source emission factor model (MOBILE4); and (2) effect of budget constraints on MOBILE4 reliability.

GAO found that: (1) in order to enhance MOBILE4 reliability, EPA needed to define MOBILE4 assumptions; (2) although EPA had not determined the overall reliability of MOBILE4, EPA believed that its statistical reliability should surpass the previous version's; (3) EPA continued to develop and update model assumptions, which should improve the reliability of the next version; (4) MOBILE4 remained an important tool to understanding efforts to limit and decrease air pollution; (5) funding constraints limited EPA ability to perform emission testing of later motor vehicles, so MOBILE4 estimates were less reliable than its projections for earlier model years; (6) EPA addressed funding inadequacies by providing increased funds in fiscal year (FY) 1989 and FY 1990; and (7) EPA funding for MOBILE4 increased from $807,000 in FY 1988 to $1.5 million in FY 1989 and $2.1 million in FY 1990.

Mar 1, 2021

Jan 22, 2021

Jan 19, 2021

Jan 15, 2021

Jan 13, 2021

Jan 7, 2021

Dec 18, 2020

Dec 9, 2020

Looking for more? Browse all our products here