Appendix F 

Effect of Senior Exemption on 2002 

Highway Mobile Source Emissions 
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): 

AGE VEHICLES

10 years 1,629 

11 years 2,120 

12 years 2,239 

13 years 2,630 

14 years 2,496 

15 years 2,350 

16 years 2,369 

17 years 2,227 

18 years 1,708 

19 years 1,111 

20 years 669 

21 years 586 

22 years 496 

23 years 833 

24 years 794 

25 years 44 

F-1 
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)

x

was divided by the total summer-adjusted 2002 VMT (122,754,275 miles) with a 

resulting overall grams-per-mile NOx 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. 

x

• 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 fractions,1

 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 

 

1

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

traveled by each vehicle type. 

F-2 
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 NO reduction credit loss for 2002 was determined to be 0.03 ton 

per day. 

x

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. 

• 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. 

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