WASHINGTON, D.C. 20460
                            APR -3 1997
                                                            OFFICE OF
                                                         AIR AND RADIATION

     As part of its  ongoing efforts to provide assistance to
States regarding in-use  testing programs and to promote
uniformity with respect  to smoke test procedures, the
Environmental Protection Agency (EPA)  is recommending the use of
the SAE J1667 procedure  for state-operated in-use testing
programs for highway heavy-duty diesel vehicles  (HDDV).  This
guidance document  provides a technical recommendation that States
can follow in the  implementation of their in-use emission testing
programs.  Because highway HDDV travel across the country, EPA
believes that the  adoption of a common smoke test procedure by
States would help  address the concerns brought up by the trucking
industry and heavy-duty  engine manufacturers by promoting
consistency between  smoke measurements in state-operated in-use
testing programs for HDDV.

     The procedure SAE J1667,  entitled Snap Acceleration Smoke
Test Procedure  for Heavy-Duty Diesel Vehicles, was developed
between 1992 and 1996 by a committee of members representing the
trucking industry, heavy-duty engine manufacturers,  test
equipment manufacturers,  and state and federal regulators.  SAE
J1667, issued in February,  1996,  recommends a smoke test method,
instrument specifications and correction factors for ambient  .
conditions, including altitude compensation.  The SAE J1667 is a
snap acceleration  test under idle conditions, using engine
inertia for loading,  and is specifically designed for identifying
excessive smoke emitters.   Since it is a non-moving vehicle test,
the SAE J1667 can  be conducted along the roadside or in a test

     The Clean  Air Act Amendments of 1990 do not require states
to implement in-use  testing programs for highway HDDV.  However,
as a means to address concerns about in-use emissions from HDDV,
many states today  are implementing in-use smoke testing programs.
Excessive emission of black smoke from HDDV is one of the most
common complaints  received from the public by state and local air
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quality agencies.  Since the excessive emission of black smoke is
often an indicator that an engine is in need of maintenance
and/or repair and gaseous/particulate emission levels may also be
high, states are focusing on black smoke opacity measurements for
their in-use testing programs.

     EPA is aware of several states which are in various phases
of considering, or have already adopted, some form of an in-use
smoke emission test for HDDV.  These states include:  Arizona,
California, Colorado, Connecticut, Illinois, Maryland,
Massachusetts, Nevada, New Jersey, New York, Ohio, Utah and
Washington.  Even though most of the state-operated in-use
programs include smoke measurements, not all programs use the
same test procedure for in-use smoke evaluations.  These
inconsistencies have created major concerns for the trucking
industry,  since trucks that travel across the country may be
subject to inspections in different states with different test
procedures.  By using similar test procedures,  states would have
the advantage of being able to compare test results.  Therefore,
testing and administrative costs could be minimized.
Furthermore,  any environmental benefits that could be derived
from the implementation of these programs would be much easier to
quantify in regions that use the same test methods.

     For the reasons cited above,  EPA believes  that uniformity in
smoke test procedures is appropriate and is recommending the use
of the SAE J1667 procedure for smoke evaluations in state-
operated in-use testing programs.   The SAE J1667 test is a peer-
reviewed procedure that has been developed by a joint government-
industry committee to provide a reliable method for in-use smoke
measurement.   The procedure is currently being  used by several
states and is viewed favorably by the trucking  industry and
highway heavy-duty engine manufacturers.
    o/T. Oge,
     e of Mobi
   ctor                  Date