3.3. Transit Bus

Staff followed the same methodology as EMFAC2021 for developing the transit bus (UBUS) inventory. The only change comes from the data sources. Staff used two main data sources for transit buses in EMFAC2025: National Transit Database (NTD) and Innovative Clean Transit (ICT) Reports. As part of the ICT regulation, all transit agencies in California are required to report their inventory annually. Hence, staff used these reports to extract the population of transit buses. However, ICT reports do not contain bus activity such as VMT. As a result, staff employed NTD reports to extract the VMT per bus at the transit agency level, estimating the VMT based on ICT report population.

EMFAC2025 used NTD and ICT reports from calendar year 2023 to develop the UBUS inventory based on ICT rule phase-in (FTA, 2024, CARB, 2024). For more details about the projections and ICT phase-in, refer to Section 4.2.3 of EMFAC2021 Technical Documentation (CARB, 2021).

Figure 3.28 and Figure 3.29 compare the UBUS populations and VMT between EMFAC2025 and EMFAC2021, respectively.

Figure 3.28: Transit Bus (UBUS) Population: EMFAC2025 vs. EMFAC2021

Figure 3.29: Transit Bus (UBUS) Vehicle Miles Traveled: EMFAC2025 vs. EMFAC2021