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30 <br />4.1 Emissions Model <br />MOBILE 6.2 was used to develop the emissions factors. Motor vehicle emissions controls <br />considered in the MOBII,E6.2 model include the following: <br />Strate~y <br />UM Program (per NC SIP) <br />Tier 2 vehicle's Emission Standards <br />Low Sulfur Gasoline and Diesel fuels <br />Heavy Duty Vehicle Rules 2004 and 2007 <br />Low RVP Gasoline <br />On board vapor recovery <br />Methodolo~v/Anyroach <br />Ran Model in Place <br />Ran Model in Place <br />Ran Model in Place <br />Ran Model in Place <br />Ran Model in Place <br />Ran Model in Place <br />Also, area specific information is used for such items as vehicle age distribution and vehicle type <br />distribution rather than national default values, as documented below. <br />4.1.1 Development of Emissions Factors <br />A critical element of any emissions analysis or estimate is the development and utilization of the <br />emissions factors applied to the travel estimates. In order to assure that the emissions factors used <br />in the conformity analysis were compatible with those used in the development of the North <br />Carolina SIP, DENR provides emission factors and model inputs for each non-attainment and <br />maintenance area in North Carolina. The MOBILE6.2 emissions factor model was used to develop <br />the emissions factors in 2009 for the Triangle. These factors are shown in Appendix F. <br />NCDENR provides motor vehicle emissions factors by federal functional classification of the <br />roadway system. In addition the percentage of motor vehicles subject to the inspection and <br />maintenance program is estimated from accident data. The scope of North Carolina's motor <br />vehicle inspection and maintenance program expanded to forty-eight counties by 2007. The <br />percentage of vehicles in each county subject to the I/M program is shown in Table 14. <br />Table 14. Percentage of Vehicles Subject to Inspection and Maintenance Programs <br />Location 2007-2035 <br />Wake Coun 95% <br />Durham Count 92% <br />Johnston Coun 91% <br />Chatham Coun 96% <br />Granville Coun 83% <br />Oran a Coun 89% <br />Franklin Coun 90% <br />4.I.2 Development of VMT Mix by Vehicle Type <br />The North Carolina Department of Transportation (NCDOT) provides data on VMT for six urban <br />and six rural road types; vehicle mix data are available for the same road types. Automatic traffic <br />recording stations and selected Highway Performance Monitoring System (HPMS) locations were <br />used and counts taken in 2007 are used to determine the percentage of vehicles, by vehicle type, <br />for various road types. Vehicle classification data was used in conjunction with MOBIL,E6.2 <br />default vehicle mix to estimate fleet distribution by functional class. The classification data was <br />22 <br />