Exhibit 4 – Senior I/M Program Details

Mobile6‐based I/M emissions were retained for this off‐model exercise because they were considered

to still be conservatively high.  In the future, GA EPD and ARC will evaluate the development of MOVES‐

based senior I/M credits.

Effect of Senior Exemption on 2002 Highway Mobile Source Emissions

During their 1996 session the Georgia General Assembly amended the Georgia Motor Vehicle Emission

Inspection and Maintenance Act (O.C.G.A. Section 12‐9, et seq), to exempt from emission testing those

otherwise subject vehicles ten years old or older driven fewer than 5,000 miles per year and owned by

persons 65 years old or older.  

The actual numbers of vehicles that received senior citizen exemptions from Georgia's inspection and

maintenance (I/M) program waiver centers in 2002 are shown in the table below (source: Appendix I,

Detailed List of Waivers Processed, from 2002 Annual Operations Report for Georgia's Enhanced

Inspection and Maintenance Program, July 30, 2003):

Table 1 – Vehicles with Waivers by Year

Age (years) Vehicles

10 1,629

11 2,120

12 2,239

13 2,630

14 2,496

15 2,350

16 2,369

17 2,227

18 1,708

19 1,111

20 669

21 586

22 496

23 833

24 794

25 44

2002 NOx Credit Loss

MOBILE6.2 emission factors for calculating the 2002 NOx credit loss from these exempted vehicles were

determined in the following manner. Six combined highway mobile source control strategies were

modeled:  

• enhanced I/M in all 13 Atlanta ozone nonattainment area counties;  

• the Federal Motor Vehicle Control Program, including Tier 1 and Tier 2 tailpipe standards;  
• Stage II vapor recovery;  

• low‐sulfur (150 parts per million, or ppm) and low Reid Vapor Pressure (7.0 pounds per square

inch, or psi) gasoline;  

• the National Low Emission Vehicle (NLEV) program; and  

• technician training and certification).  

The enhanced I/M program is a decentralized annual hybrid with onboard diagnostics (OBD‐II) system

checks on 1996 and newer model year vehicles; and two‐mode ASM tests on 25‐year‐old through 1995

model year vehicles. Anti‐tampering inspections (checking for catalyst removal) are performed on 25‐

year‐old through 1995 model year vehicles, and gas cap pressure tests are performed on all vehicles

subject to inspection.  

• An overall 2002 highway mobile source NO inventory based on July 1, 2002, MOBILE6.2 emission

factors with all controls in place (310,382,142 grams per day) was divided by the total summer‐

adjusted 2002 VMT (122,754,275 miles) with a resulting overall grams‐per‐mile NO emission

factor of 2.528.

• MOBILE6.2 runs with all subject vehicles receiving their appropriate test were performed to

determine the speed that would result in a July 1, 2002, NO emission factor of 2.528 grams per

mile: 38.58 miles per hour.

• Two separate July 1, 2002, MOBILE6.2 runs, at 38.58 mph and with emissions calculated by model

year, were made: one with hybrid I/M on 25‐year‐old and newer subject vehicles; the other with

OBD‐II system checks on 1996 and newer vehicles, with 1995 and older vehicles exempted.  

• Next, both sets (covered and exempt) of emission factors were separately multiplied by the VMT

fractions1

, normalized to total 1.000, for the appropriate vehicle types (LDGV, LDGT12, LDGT34),

and the three products were then added together to produce a single passenger vehicle

emission factor for each exempted vehicle age.  

• The differences in the covered and exempt emission factors were then determined for each

exempted vehicle age, these differences were multiplied by 4999, the maximum allowable

yearly miles traveled by exempt vehicles, and that product was then multiplied by the number

of vehicles of that age to determine grams per year.  Grams per year were converted to tons per

day (907,180 grams per ton, 365 days per year) and the resulting NOx reduction credit loss for

2002 was determined to be 0.03 tons per day.

2002 VOC Credit Loss

MOBILE6.2 emission factors for calculating the 2002 VOC credit loss from these exempted vehicles were

determined in the following manner:  

• An overall 2002 highway mobile source VOC inventory based on July 1, 2002, MOBILE6.2 emission

factors with all controls in place (158,026,372 grams per day) was divided by the total 2002 VMT

(122,754,275 miles) with a resulting overall grams‐per‐mile VOC emission factor of 1.287.  

• MOBILE6.2 runs with all subject vehicles receiving their appropriate test were performed to

determine the speed that would result in a July 1, 2002, VOC emission factor of 1.287 grams per

mile: 30.6 miles per hour.  

                                                            

1 An output of MOBILE6.2, the VMT (vehicle miles traveled) fraction is the fraction of total VMT traveled by each

vehicle type
• Two separate July 1, 2002, MOBILE6.2 runs, at 30.6 mph and with emissions calculated by model

year, were made: one with hybrid I/M on 25‐year‐old and newer subject vehicles; the other with

OBD‐II system checks on 1996 and newer vehicles, with 1995 and older vehicles exempted.  

• Next, both sets (covered and exempt) of emission factors were separately multiplied by the VMT

fractions, normalized to total 1.000, for the appropriate vehicle types (LDGV, LDGT12, LDGT34),

and the three products were then added together to produce a single passenger vehicle

emission factor for each exempted vehicle age.  

• The differences in the covered and exempt emission factors were then determined for each

exempted vehicle age, these differences were multiplied by 4999, the maximum allowable

yearly miles traveled by exempt vehicles, and that product was then multiplied by the number

of vehicles of that age to determine grams per year. Grams per year were converted to tons per

day (907,180 grams per ton, 365 days per year) and the resulting VOC reduction credit loss for

2002 was determined to be 0.05 tons per day.