Low-Carbon Technology Pathways for Soot-Free Urban Bus Fleets in 20 Megacities

This study shows that in almost all cases, a switch away from dedicated CNG and diesel buses can be justified not only to achieve soot-free emissions but also to generate the greatest climate benefits from a future technology transition. Certain non-fossil fuels should be avoided entirely, such as palm oil biodiesel. And in at least two megacities—Johannesburg and Morocco—dedicated CNG or Euro VI diesel hybrid engines may provide a narrow climate benefit over some of the non-fossil alternatives. The introduction of some low-carbon fuels can take advantage of existing refueling infrastructure and deliver meaningful climate benefits, such as bio-CNG from landfill or digester gas and biodiesel from plant oils or animal fats. But, on the whole, zero-emission electric drive buses appear to provide the greatest magnitude of climate benefits for the greatest number of routes in the largest number of cities.