November 22, 1996

                  Comments on Use of MOBILE5b

On October 11, 1996, the Office of Mobile Sources (OMS) released
an interim version of the highway vehicle emission factor model
for use in recalculation of 15% VOC reductions by the States and
others.  This model and the release memo were mailed to all EPA
Regional Offices and posted on the Technology Transfer Network
(TTN) computer bulletin board system (BBS).  The reader is
referred to the release memo for additional details.

In releasing MOBILE5b, OMS made clear that no parties are
currently required to use MOBILE5b, and that we seek comment from
affected parties as to when the use of this version of the model
is appropriate, when if ever use of this version should be
required, and explanation of the impact that this model version
might have on various ongoing analyses, including conformity
determinations.  This message provides additional information on
what comments are being solicited, how comments should be
submitted to OMS, and what will be done after the comment period
has closed.

In the release memo, OMS noted that we were providing sixty (60)
days for comments to be submitted on the following issues:  How
does release of MOBILE5b impact the SIP process?  How does
release of MOBILE5b impact conformity evaluations?  When and
under what conditions would it be advantageous, and when and
under what conditions would it be disadvantageous, for parties to
use MOBILE5b over MOBILE5a?  What issues need to be addressed in
any guidance on using MOBILE5b?  The reader is referred to the
release memo for a more complete discussion.

Taking into account the scope of the issues on which comment is
solicited and the approaching holiday season, OMS has determined
that it would be appropriate to accept comment through
December 31, 1996.  Comments on when and how MOBILE5b should or
should not be used, when its use should or should not be allowed
or required, and when it is advantageous or disadvantageous to
use MOBILE5b rather than MOBILE5a, may be submitted in three
ways:

1.   By mail -- Send comments to:  U. S. EPA - NVFEL
                              Assessment and Modeling Division
                              2565 Plymouth Road
                              Ann Arbor, MI  48105

2.   By fax -- Send comments to:        (313) 741-7939

3.   By e-mail -- Send comments to:     MOBILE@epamail.epa.gov

In all cases, commenters should clearly indicate that what is
being submitted is "Comments on Use of MOBILE5b."