'Greenhouse gas emmisions'?
Does this include the source power generation? Of course not, because some regions use wind/solar/nuclear, which have a vastly different greenhouse gas emmsiions then others.
Why not use SIMPLE standard units. It's up to the buyers to know the source of the fuel.
N/m@0-10km/h, 11-50km/h, 51-80km/h, 81-100km/h
All cars can compete on this scale. If a 3000kg SUV takes 40kN/m to go from 0-10km/h, and an all electric 1000kg Prius takes 5kN to achieve the same task, we can figure out what is better.
They should also mandate the energy density be displayed at all fuel pumps/charging stations.
natural gas: 200N/L
(my mind is fuzzy on how to apply this to all-electric, but plenty of the folks on here are smarter then I am), but my point still stands.
Label everything based on the one common denominator: energy.