By Nichola Groom, Thomson-Reuters.
Fifteen years ago, California led the way to cleaner transit buses with strict tailpipe emissions standards that effectively ushered out diesel as the primary fuel for buses in the state and replaced it with natural gas.
Now, California is poised once again to take the lead, this time by mandating a switch to so-called "zero-emission" buses by 2040.
The new push by California's powerful Air Resources Board (CARB) has the potential to marginalize natural gas as a bus fuel in the same way its adoption once marginalized diesel.
In response, the California Natural Gas Vehicle Coalition has proposed expanding the definition of "zero-emission vehicles" to include not just electric buses, but also those powered by so-called "renewable natural gas," which is produced from cow manure or decomposing organic matter in landfills.