CO$_{2 }$(metric tons)  =  Fuel Usage (gallons) x 19.643 pounds CO$_{2 }$per gallon x short ton per 2,000 pound  x 0.907185 metric ton per short ton  CH$_{4 }$(metric tons)  =  Fuel Usage (gallons) x 0.000003 pounds CH$_{4 }$per gallon x short ton per 2,000  pound x 0.907185 metric ton per short ton  N$_{2}$O (metric tons)  =  Fuel Usage (gallons) x 0.00000023 pounds N$_{2}$O per gallon x short ton per 2,000  pound x 0.907185 metric ton per short ton  CO$_{2e }$(in metric tons) = CO$_{2 }$+ CH$_{4 }$x 34 + N$_{2}$O x 298  Equation C-9. CO$_{2e }$Emission Calculation of Gasoline GSE  C.2.4 Ground Access Vehicles  66  Ground access vehicles exclude those ground support equipment (GSE) used for servicing aircraft and airport.  69$_{ }$ In general, the computation and data inputs for computing motor vehicle GHG emissions are  similar to those used for computing motor vehicle criteria pollutants (see  Appendix A4 ,  Ground  Access Vehicles Emissions Inventory for Criteria Pollutant s ). As discussed,  some airports  monitor and collect information on the overall movement of traffic through the use of automatic  vehicle identification (AVI) systems. Other airports track fuel usage for some types of vehicle  operations (e.g., parking shuttle buses, rental car shuttles, airport fleet vehicles). Traffic volumes  can also be estimated based on passenger surveys and enplanement data.  From these data, the ground access vehicle usage (either in miles traveled or fuel usage) can be  determined.  The EPA’s MOVES model is then used to estimate fuel consumption  rates (in  gallons per mile) and  CO$_{2}$, CH$_{4}$, and N$_{2}$O emission factors (in grams per mile) based on  the  vehicle fleet mix.  Emissions from ground access vehicles are generally a function of traffic volumes , distances  traveled, vehicle operating characteristics, and fuel type. They are also typically associated with  three different types of vehicles trip types:  (i) those traveling within on- and off-airport  roadways, (ii) those traveling within airport parking facilities; and (iii) those accessing terminal  curbside areas associated with passenger pickup and drop-off.  The following section discusses the methodologies for computing  GHG emissions from ground  access vehicles. Ground access vehicles 66  encompass airport passenger vehicles (e.g., private  autos, taxis, limousines, shuttles, vans, buses, rental cars, etc.), vehicles transporting airport and  tenant employees, airport fleet (e.g., buses, shuttles, etc.), and vehicles transporting cargo to and  from airport as well as circulating around the airport.  APPENDIX C$_{ }$