February 18, 1998


Document Released for Stakeholder Review and Comment

Trip Length Activity Factors for Running Loss and Exhaust Running
Emissions

Report Number M6.FLT.005

     The Office of Mobile Sources, Assessment and Modeling Division,
announces the release of "Trip Length Activity Factors for Running
Loss and Exhaust Running Emissions" for stakeholder review and
comment.  This document M6FLT005.PDF/M6FLT005.WPD is available at the
MOBILE6 section of the OMS Web Site (http://www.epa.gov/omswww/models.htm).

     MOBILE6 will compute and report hourly emission factors for
start, running, and evaporative emissions.  These outputs will be in
addition to the standard daily emission estimates which are currently
calculated by MOBILE5.  The hourly emission factors will allow the
MOBILE6 model to provide more precise output that accounts for the
time of day that vehicle emissions occur.

     This document describes the data and methodology used to
calculate running loss and exhaust emission length activity factors.
The data used in the analysis were collected from two instrumented
vehicle studies.  The results of the analysis will be built into the
MOBILE6 model as data parameters.  These results are shown in tabular
form in the document.  The results include three distributions.  These
are: (1) estimates for the number of vehicle trips per day, (2) a
distribution of trips by hour weighted by vehicle miles travelled
(VMT), and (3) the hourly VMT distribution by trip length (in units of
time).  In addition, the three distributions were stratified by
weekday and weekend.  These distributions will be used with the
corresponding vehicle running loss emissions data and running exhaust
emission data in MOBILE6 to estimate hourly running loss and exhaust
emission rates.

     Comments on this report and its proposed use in MOBILE6 should be
sent to the attention of Ed Glover.  Comments may be submitted
electronically to mobile@epamail.epa.gov, or by fax to (313)741-7939,
or by mail to "MOBILE6 Review Comments", US EPA Assessment and
Modeling Division, 2565 Plymouth Road, Ann Arbor MI 48105.  Electronic
submission of comments is preferred.  In your comments, please note
clearly the document that you are commenting on including the report
title and the code number listed. Please be sure to include your name,
address, affiliation, and any other pertinent information.

This document is being released and posted on February 18, 1998.
Comments will be accepted for sixty (60) days, ending April 19, 1998.
EPA will then review and consider all comments received, and will
provide a summary of those comments and how we are responding to them
in the form of a followup document within 30 days after the close of
the comment period (by May 18, 1998).


Thank you for your continuing interest in the development of MOBILE6.

Sincerely,

Emission Inventory Group, Assessment and Modeling Division
US EPA Office of Mobile Sources