These are not carbon neutral, a vehicle emits CO2 when burning them and that is not captured even in half by the growing plants.+
And you have to fertilize them for this efficiency, and those either require non-neutral manufacturing process, or composting which releases methane (in itself a biofuel that could be used but isn't). Plants also release some methane on their own when growing.
That's not even counting loss of biodiversity or replacing carbon-negative fields, farming grasslands and forests.
You could make a biofuel carbon neutral but we're not even close. Bioethanol for example has a CO2 producing fermentation step.
Going biohydrogen and burying the plants could work. (Even methane is not clean enough to offset planting, unfortunately.)
And we do not want to go neutral but to reduce emissions.
I'm not here to pettifog about various definitions, studies and calculation methodologies. "Literally impossible" was claimed but now requires, uh, interpretations.
Electric vehicles are far more promising and compelling as a large scale solution to replace most existing consumer ICE transportation, but there are probably some roles for ICE vehicles using carbon neutral fuels.
And you have to fertilize them for this efficiency, and those either require non-neutral manufacturing process, or composting which releases methane (in itself a biofuel that could be used but isn't). Plants also release some methane on their own when growing.
That's not even counting loss of biodiversity or replacing carbon-negative fields, farming grasslands and forests.
You could make a biofuel carbon neutral but we're not even close. Bioethanol for example has a CO2 producing fermentation step. Going biohydrogen and burying the plants could work. (Even methane is not clean enough to offset planting, unfortunately.)
And we do not want to go neutral but to reduce emissions.
-- +) The number is 37% according to in-depth study: http://theconversation.com/biofuels-turn-out-to-be-a-climate...