California’s transportation and power generation sectors emit more than 50 percent of the state’s greenhouse gas (GHG) emissions. The state GHG emission mitigation goals include reducing GHG emissions to 1990 levels by 2020. Additionally, to improve air quality throughout the state, aggressive criteria pollutant emission standards have been established for both sectors. Transitioning from fossil fuels to renewable fuels is one strategy to meet these environmental goals. Landfills and wastewater treatment plants are a source for the production of alternative fuels like renewable natural gas (RNG) and hydrogen (H2) which could then be used in either sector. To evaluate this strategy, the impact on GHG and criteria pollutant emissions, and on air quality resulting from the production and use of RNG in zero or near-zero emission medium-duty vehicles (MDV) and heavy-duty vehicles (HDV) are analyzed. The research reveals that (1) RNG produced from biogas is the most cost effective strategy to utilize the limited resource of biogas available in California even though H2 is the most attractive fuel, (2) the transportation sector is the more effective sector for the use of RNG fuel, (3) MDV and HDV outfitted with commercially available near-zero emission CNG engines with RNG results in substantial reductions in both GHG and criteria pollutant emissions, and significantly improves air quality than the use of H2 in LDV, and (4) the reductions in GHG and criteria pollutant emissions and improvements in air quality exceed those achieved with the MDV and HDV populations envisioned by the State Implementation Plan (SIP).