3.4. Natural Gas Vehicles

Following the same methodology used in EMFAC2021, staff incorporated the most recent vehicle registration data acquired from DMV to update the natural gas module. Similar to EMFAC2021, staff used two prediction classes: a flat average and a linear regression class. The flat average class assumes a constant fraction of natural gas penetration, while the linear regression class assumes that the natural gas fraction increases as a function of model year until it reaches 100%. As in EMFAC2021, EMFAC2025 applied fractions obtained from the DMV directly. Figure 3.30 compares the heavy-duty natural gas population in EMFAC2021 and EMFAC2025. For more details regarding the methodology, please refer to EMFAC2021 Technical Documentation Section 4.2.4 (CARB, 2021).

Figure 3.30: Projected Statewide Heavy-Duty Natural Gas Population