Achieving NOx and Greenhouse gas emissions goals in California’s Heavy-Duty transportation sector

•Meeting California’s South Coast emissions goals difficult under all scenarios.•Accelerating fleet turnover is likely the most important NOx control strategy.•Encourage renewables fueled Heavy-Heavy-Duty Near-Zero-Emission Vehicles. We evaluate the NOx and greenhouse gas (GHG) emissions trends of the Heavy-Duty (HD) transportation sector in California’s South Coast region, under four future scenarios with varying deployment trends of near-zero-emission vehicles and zero-emission vehicles (NZEV and ZEVs) over two decades. Modeling analysis using original vehicle population projections and real-world NOx emission factors, are used to estimate emissions over the 2020 to 2040 timeframe. Analysis shows that emissions are significantly impacted by the rate of deployment of cleaner technology options. GHG results show that very aggressive deployment of low carbon technologies is necessary to achieve 2040 emission targets. The results show accelerating the fleet turnover to be a more important NOx control strategy than dividing the vehicle replacement between NZEVs and ZEVs. The analysis suggests that Heavy-Heavy-Duty (HHD) NZEVs should be encouraged in the near to mid-term, and even long-term, if operated on renewable natural gas.