U.S. Environmental Protection Agency      Office of Mobile Sources

September 16, 1997

Update of Fleet Characterization Data for Use in MOBILE6

Released for Stakeholder Review and Comment


The Office of Mobile Sources, Assessment and Modeling Division,
announces the release of “Update of Fleet Characterization Data for
Use in MOBILE6" for stakeholder review and comment. This document
(M6FLT001.PDF) is available at the MOBILE6 section of the OMS Web
Site (http:/www.epa.gov/omswww/models.htm).

The aforementioned report was developed by Acurex Environmental
Corporation under contract for the EPA Office of Mobile Sources. The
report attempts to characterize the national vehicle fleet, based on
a “snapshot” as of July 1, 1996. The fleet data is disaggregated into
eighteen categories based on fuel type and gross vehicle weight (GVW)
class. The report includes a summary of the data sources employed,
the data analysis methodologies, and the results of the analysis.

During the development of this report, the contractor, was made aware
of the impending release of new data characterizing light-duty
vehicle annual mileage accumulation rates. The current report relies
on data from a survey study, conducted by the U.S. Department of
Transportation, known as the 1990 Nationwide Personal Transportation
Survey (NPTS). The new data is in the form of a 1995 NPTS study
which, unlike the 1990 version, includes actual odometer readings
(past versions of this study relied on auto owner’s estimates of
mileage). In light of this newly developed data, EPA is issuing an
additional work assignment to Acurex Environmental; this work
assignment will require the contractor to recalculate mileage
accumulation for light-duty vehicles based on the 1995 NPTS study
data.

As part of EPA’s internal review of this report, a possible data
error was discovered. There appears to be a problem with the
reporting of truck registrations above and below 8,500 lb GVW. The
dividing line for regulatory emission standards for light-duty
vehicles and heavy-duty engines is defined by vehicles weighing up to
8,500 lb GVW and vehicles weighing above 8,500 lb GVW, respectively.
As the heavy-duty standards are less stringent than the light-duty
standards, it is important to accurately characterize the number of
trucks above and below 8,500 GVW. Acurex reported the following split
of diesel trucks below 10,000 lb GVW:

                              Model Year

GVW Range      1990    1991    1992    1993     1994     1995

0-8,500       69,433  74,807  87,028  125,823  136,342  168,267
8,500-10,000  72,117  77,685  93,290  133,923  131,869  162,857


The total number of 0-10,000 lb GVW diesel trucks reported by Acurex
is reasonably consistent with reported sales data. However, their
roughly 50/50 split above and below 8,500 lb GVW does not appear to
be reasonable. According to some sources, only General Motors offered
a light-duty diesel during this period and, according to reports in
Automotive News, even GM sold mostly heavy-duty diesels. The popular
Cummins turbo-diesel sold in Dodge pickup trucks and the Navistar
diesel sold in Ford pickup trucks and full-size vans are certified
only to heavy-duty engine standards and are not available in vehicles
under 8,500 lb GVW (i.e., LDDTs). Thus, the large majority of diesels
sold in 0-10,000 lb GVW trucks are in trucks above 8,500 lb GVW. This
is not reflected in the R. L. Polk data used by Acurex in this
report.

Data reported in the 1996 Fuel Economy Trends Report supports the
case that relatively few diesels are sold vehicles below 8,500 lb
GVW. The following table presents approximate diesel sales using the
diesel fuel metering percentage in Table E-4 of the Trends Report:

                           Model Year

GVW Range    1990   1991   1992    1993    1994    1995

0-8,500      6,000  6,000  3,000  <2,000  <2,200  14,000


The problem might lie in the registration data reported to R.L. Polk.
The traditional 3/4 ton pickup truck, such as the Ford F250 and the
Dodge D250, is available with a variety of GVW ratings. While the
base 3/4 ton pickup trucks are under 8,500 lb GVW, there are optional
load packages with GVW ratings above 8,500 lb. If the registration
data only reports vehicle models and does not include a GVW rating,
it would likely result in the recording of all 3/4 ton pickups as
under 8,500 lb GVW. Note that, if this is the case, then there may be
some under prediction of gasoline engines in the 8,500-10,000 lb GVW
range as well, of roughly the same order of magnitude (e.g. about
100,000 to 150,000 vehicles in 1995).

Please note that EPA is seeking any input from stakeholders and
reviewers that might aid us in addressing and resolving this issue.

Comments on this report and its proposed use in MOBILE6 should be
sent to the attention of Tracie Jackson. Comments may be submitted
electronically to jackson.tracie@ epamail.epa.gov, or by fax to (313)
741-7939, or by mail to “MOBILE6 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 September 17, 1997.
Comments will be accepted for sixty (60) days, ending November 16,
1997. 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 follow-up document within 30 days of the close
of the comment period.

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

Sincerely,

Emission Inventory Group, Assessment and Modeling Division, US EPA

Telephone: (313) 741-7903; fax (313) 741-7939
Email: mobile@epamail.epa.gov