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.

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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.

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