APPENDIX A
                                    
            Instructions for the Use of Hybrid and
         Technician Training and Certification Credits
                                    
                  (User's Guide for MOB5a_H)

     The emissions benefits of the technician training and 
certification program discussed in Enclosure 2, and of the 
retest-based hybrid I/M program option discussed in Enclosure 3, 
cannot be modeled using the standard release version of MOBILE5a 
(26-Mar-93).  A specially modified version of MOBILE5a has been 
developed and is being released to deal specifically with these two 
program options.  This version of the model is called MOB5a_H.  This 
attachment (which can be inserted in the User's Guide to MOBILE5) 
describes how these two programs can be modeled.

     The enclosed MOB5a_H diskette contains all of the files needed to 
use the new retest-based hybrid (RBH) and technician training and 
certification (TTC) program options.  It includes seven (7) files 
necessary to run the model:

       MOB5a_H.EXE
       MOB5a_H.S
       HYBRID.IMC
       IMDATA3.D
       PPEFF.D
       PPEFFM5.D
       TTC.D

     The first of these is the compiled, executable file of the new 
version of the standard MOBILE5a model, which has been altered to 
include the new I/M program options.  The only modifications that were 
made to MOBILE5a in order to create MOB5a_H were those required to 
permit the calculation of emissions credits with a RBH I/M program 
design and/or with TTC added to an I/M program.  If neither of these 
options are used, then MOB5a_H will produce exactly the same emission 
factors as are produced by MOBILE5a.

     The second file is simply the FORTRAN source code for MOB5a_H.  
If you intend to run the model on your DOS-based PC, you should not 
require this source code file.  The last five files, however, are data 
files which should be kept in the same directory as the altered model 
MOB5a_H.  Several other files which are necessary, and which are 
distributed with the standard release of MOBILE5a, have not been 
included in this distribution in order to save space.  These three 
files, which are listed below, should be duplicated and also put in 
the directory with the altered version of MOBILE5a.  (As an 
alternative, the seven new files listed above can be put in the same 
directory as the standard MOBILE5a release, allowing the three files 
listed below to be shared for use by MOBILE5a or MOB5a_H).

       F77L3.EER
       TECH12.D
       IMDATA.D

     This new version of the MOBILE5a model must be used in order to 
properly determine the impact of Retest Based Hybrid (RBH) programs or 
Technician Training and Certification (TTC) on I/M program credits.  
In order to reduce the changes needed in the MOBILE model code and so 
to provide the ability to model these types of program options as 
quickly as possible, the new options have not been fully integrated 
into MOBILE, and so the use of this version requires careful 
manipulation of the data files.  It will be entirely possible to 
incorrectly determine the results needed and to be unable to detect 
the problem.  Therefore, if the emission factors produced from a given 
scenario seem to be too large or too small, the modeler is advised to 
carefully re-run that case, paying very close attention to the data 
files and how they are being used.


Age-Based Hybrid Programs

     The MOBILE5a model has always been able to be used to model an 
Age-Based Hybrid I/M program design by manually setting the model year 
ranges covered by each program element for each calendar year of 
evaluation.  This is done by having a different program type 
(test-only or test-and-repair) for each of the two I/M Program 
Descriptive Records with separate (non- overlapping) model year 
coverages.  (Note:  The modeler should also consult Section 2.2.5 of 
the User's Guide to MOBILE5, which discusses the two I/M Program 
Descriptive Records and their use in detail, when setting up model 
runs.)  When running an Aged-Based Hybrid program design, do not use 
any of the Retest-Based Hybrid I/M credits or data files described 
below.

     The following equations show how to determine the MOBILE5a inputs 
for Last Model Year and First Model Year for each of the I/M Program 
Descriptive Records for the runs in order to model the Age-Based 
Hybrid:


Test-only Group (where older vehicles are required to get their 
initial test (and retests) at test-only facilities) :

First Model Year of Test-only Group  =  Oldest Model Year to be Tested

Last Model Year of Test-only Group  =  Evaluation Year - (Age of First 
                                       Test at Test-only + 1)


Test-and-Repair Group (where new vehicles are allowed to get their 
initial test (and retests) at test-and-repair facilities)

First Model Year of Test-and-Repair Group  =  Last Model Year of 
                                              Test-only Group + 1

Last Model Year of Test-and-Repair Group  =  2020


     For modeling the complete exemption of new vehicles (i.e., 
starting testing after two years old) the following equation should be 
used to figure the input for Last Model Year:

Last Model Year  =  Evaluation Year - (Age at First Test + 1)

     Any state interested in modeling one of these options should 
contact EPA Regional Office staff for assistance in performing the 
modeling.


Retest-Based Hybrid Programs

     There are two distinct parts to this scenario, the effect of the 
retest-based hybrid (RBH) option on exhaust emissions, and the effect 
on evaporative emissions.  The RBH program credits for exhaust 
emissions are stored in the data file HYBRID.IMC.  This file contains 
the RBH program effects for all of the I/M program test types and 
cutpoint choices found in the original MOBILE5a I/M credit files.  
This data file is substituted for the data normally read from the data 
file IMDATA.D.

     To avoid confusion, EPA recommends that the I/M credits in the 
data file HYBRID.IMC be accessed using the alternate I/M credit option 
found in the I/M Program Descriptive Record, described in Chapter 2, 
Section 2.2.5, in the "User's Guide to MOBILE5."  Essentially, if the 
appropriate alternate I/M credit flag for 1981 and newer vehicles is 
set to 2, then the user simply adds the name of the file which 
contains the alternate I/M credits (along with the directory path, if 
necessary) as an additional record following the last I/M Program 
Descriptive Record.  Be sure that the I/M credit flag is set in the 
first I/M Program Descriptive Record.  The location for the I/M credit 
flags in the second I/M Program Descriptive Record are used simply as 
space holders and are not read or used by MOBILE5a. 

     The enclosed MOB5a_H diskette also contains example input and 
output files used to estimate retest-based hybrid (RBH) and technician 
training and certification (TTC) program benefits.  All input files 
use the extension *.IN and the corresponding output file uses the 
extension *.OUT.  The included example input files are:

       ANNUAL.IN
       BITOIM24.IN
       BITOASM.IN
       BIHYIM24.IN
       BIHYASM.IN
       BIABHY5.IN
       BIABHY7.IN
       IDLE1TO.IN
       IDLE2TR.IN
       ASM5TR.IN

     See the hardcopy of the example files that are included at the 
end of this attachment for an illustration of an input file for 
MOB5a_H that is set up in accordance with these directions. (Note:  
The modeler should also consult Section 2.2.5 of the User's Guide to 
MOBILE5, which discusses the two I/M Program Descriptive Records and 
their use in detail, when setting up model runs.)

     Since the credits for RBH I/M programs are themselves already a 
mix of test-only and test-and-repair option credits, the user must 
indicate the RBH program option using a new Program Type value of 4 in 
any I/M Program Descriptive Record(s) used.  Once the alternate I/M 
credits have been read in for a MOB5a_H run, all further I/M program 
credit calculations for 1981 and newer vehicles will assume the use of 
RBH credits.  The benefits for the pre-1981 model year vehicles are 
adjusted to reflect the RBH program design if the Program Type flag is 
set 

     If the modeler wishes to include the effects of both RBH, and 
either standard test-only or test-and-repair, program elements (e.g., 
for different calendar years of evaluation, with a standard program 
through a given year and an RBH program after that; or, for a program 
that applies RBH and a standard program option for vehicles on the 
basis of model years), this will require separate MOBILE runs.  This 
situation cannot be modeled by using the two I/M Program Descriptive 
Records in a single model run.

     The effectiveness of the functional pressure and purge tests at 
reducing evaporative emissions are contained in a credit array named 
PPEFF in the MOBILE model.  There is no user input to override this 
credit array provided in MOBILE5a.  EPA has modified MOB5a_H to read 
the credit array for pressure and purge test effectiveness from a data 
file named PPEFF.D, which has been distributed with MOB5a_H.  As a 
result, the effectiveness of the pressure and purge checks using 
MOB5a_H can be altered by changing the contents of the PPEFF.D data 
file. MOB5a_H will always read the PPEFF.D file, so that file must 
always be located in the same directory as MOB5a_H and must always be 
named PPEFF.D. The user does not need to make any changes in the 
PPEFF.D input file provided with MOB5a_H in order to obtain emission 
factors for evaporative emissions that reflect the RBH effectiveness.

     However, if the RBH effectiveness on prressure and purge testing 
is not desired, the contents of the PPEFF.D file will need to be 
changed to be consistent with the pressure and purge effects included 
in the original release of MOBILE5a.  This can be accomplished through 
use of the file PPEFFM5.D, which duplicates the credit array contained 
in the standard MOBILE5a program, and which is included with this 
release of MOB5a_H.  Since the program will always read the file named 
PPEFF.D, as discussed in the preceding paragraph, this approach 
requires careful renaming of files and tracking of the resulting file 
name/content combinations.

     If the modeler wants to include the RBH effectiveness on the 
pressure and purge test benefits, then PPEFF.D as supplied should be 
used.  However, if the modeler does not want RBH effectiveness 
included in the evap credits, then the file supplied with this release 
named PPEFFM5.D (containing the original MOBILE5a credits for pressure 
and purge) must be renamed PPEFF.D (since that is the file that 
MOB5a_H always reads), and the file supplied with this release that is 
named PPEFF.D must be renamed with some other name (since two files in 
the same directory cannot have the same exact name).  The 
possibilities of confusion in this area are great, and extreme care is 
recommended in attempting to model these situations.


Technician Training and Certification Benefits

     The Technician Training and Certification (TTC) effects on I/M 
program benefits are modeled using an additional data file named 
TTC.D, which has been included with the MOB5a_H.EXE file.  This file 
contains the additional benefits added to the standard I/M credits 
used by the MOBILE model.  This file is automatically read by 
MOB5a_H.EXE, and therefore must always reside in the same directory as 
the executable file.  To activate the TTC benefits, the user must set 
the TTC flag, which is located in the space immediately to the right 
of the IMFLAG located in the Control Section when using the vertical 
input option.  See the example MOB5a_H input file illustrating this 
option at the end of this attachment.  (See also Chapter 2, Section 
2.1 of the "User's Guide to MOBILE5".)  Note that the TTC option is 
not available when using the horizontal input option.

     The new TTC flag has two possible values:

      1 = No TTC effects (default; assumed if no value entered)
      2 = Full (100%) TTC benefits

     The TTC effect will be added to the I/M program benefits for all 
1981 and newer passenger cars and light-duty trucks, regardless of 
test type, frequency, or cutpoints.  The benefits for TTC are already 
assumed in the base credits for pre-1981 model year vehicles, and are 
not changed by using the TTC flag.  The additional benefits from TTC 
will be reduced by the same discount as is applied to the standard I/M 
credits for users choosing the test-and-repair program option.  
Setting the program test type to indicate a Retest Based Hybrid (RBH) 
program will slightly reduce the TTC benefits reflecting the reduced 
level of repairs in a RBH program.

     As noted above, the correct use of data files is critical to the 
correct modeling of the situations described (RBH program, TTC program 
as addition to other program types, RBH with TTC addition, whether or 
not evaporative emissions tests are to be modeled using RBH and/or 
TTC).  The most likely situations to be modeled are listed below with 
notes on the model and data file(s) to be used to obtain the correct 
results.


1.   If TTC effects are to be included, but no RBH effects for exhaust 
or evap emissions (i.e., the program is a pure test-only or a pure 
test-and-repair program), then:  Use MOB5a_H with the optional TTC 
flag set to 2 and with the PPEFFM5.D file supplied on the diskette 
renamed PPEFF.D (and the supplied file PPEFF.D renamed something else, 
as detailed above).

2.   It is possible to model the exhaust benefits to be RBH-based, but 
the evap benefits to be the standard evap benefits by using MOB5a_H 
with the PPEFFM5.D file supplied on the diskette renamed PPEFF.D (and 
the supplied file PPEFF.D renamed something else, as detailed above).



ASM2 Test Procedure

     It has always been possible to model the Acceleration Simulation 
Mode (ASM) test procedure using MOBILE5a using the special I/M credit 
file released in September 1993 and setting the alternate I/M credit 
flag on the I/M Program Descriptive Record.  These credits are 
described in the MOBILE5 User Information Sheet #3.  In MOB5a_H, a new 
level to the Test Type field on the I/M Program Descriptive Record has 
been added to allow for the use of the ASM test procedure.  Setting 
the Test Type field to "5" indicates the use of the two-mode ASM 
(ASM2) 5015/2525 test procedure and the MOB5a_H output will indicate 
the use of the ASM2 test procedure.  However, users may also continue 
to specify the Loaded/Idle test (Test Type = "3") as was done in 
MOBILE5a, and the ASM2 credits will be used.  However, the output will 
indicate the use of the Loaded/Idle test procedure.

     The new ASM2 credits have been added to the standard IMDATA.D 
file and the new file has been named IMDATA3.D.  This file can be used 
to replace the standard IMDATA.D file, since it contains all of the 
existing I/M credits, other than the hybrid options.  The Retest Based 
Hybrid version of these ASM2 credits are found in the HYBRID.IMC data 
file.  Cutpoints analyzed for the ASM2 test procedure were chosen to 
match the failure rate for the IM240 test procedure.  For example, if 
the ASM2 only the HC and CO cutpoints used in the California El Monte 
study are increased by a factor of 1.2, the failure rate of the ASM2 
matches that of an IM240 test using the standard 0.8/15/2.0 g/mi 
HC/CO/NOx cutpoints.  Since the actual ASM cutpoints used are a large 
matrice of values, the ASM2 credits can be accessed by indicating the 
corresponding IM240 test cutpoints which give the same failure rate.  
Only two additional sets of ASM2 cutpoints have been analyzed at this 
time, for the following IM240 cutpoint sets:

      0.8/15/2.0 g/mi HC/CO/NOx

      1.2/20/3.0 g/mi HC/CO/NOx