May 1, 1997

Memorandum

Subject: Air Quality Impacts of Raising the National Speed Limit

To:     Regional Air Directors
        Regional Air Branch Chiefs
        Regional Air Section Chiefs
        Regional Transportation Staff

From:   Michael Shelby
        Director, Energy and Transportation Sectors Division


Enclosed is a new study that documents likely increases in mobile source
emissions since the November 1995 repeal of national maximum speed
limits.  This analysis uses actual changes in individual state speed
limit laws.  This document provides information on likely impacts and
should be viewed as a resource for providing information to local areas
and other interested stakeholders.  More detailed analysis would
obviously be necessary for determination of emissions inventories and
for conformity.

Results of the analysis indicate that speed limit increases will
increase mobile source emissions.  Nationwide the increase in emission
levels is significant: VOC emissions are predicted to increase 2% (from
6,262,500 tons/year to 6,385,100 tons/year); NOx emissions are estimated
to increase 6% (from 9,130,800 tons/year to 9,705,700 tons/year); and CO
emissions are estimated to increase 7% (from 68,366,000 tons/year to
73,297,400 tons/year).  The report provides detailed tables on estimated
increases for each state.

The analysis uses emissions factors provided by EPA’s Mobile emissions
model.  In addition it provides a conservative estimate of increases in
emissions factors above the Mobile model’s limitation of a 65 mph
average speed.  The report also contains a case study of the emissions
impacts resulting from increased speed limits in three urban areas: the
Dallas-Fort Worth, TX MSA; the Phoenix-Mesa, AZ MSA; and the Salt Lake
City-Ogden, UT MSA. 

The analysis was performed under contract by E.H. Pechan and Associates.
For additional information, please contact Bob Noland at 202-260-2418.

cc: Gay MacGregor
    Director, Regional and State Programs Division