you could probably check with some governmental environment agencies, but that's sometimes a bit biased.
i'm more or less familiar with the fuel consumption per passenger per 100km of the LH
fleet and it ranges from something like 4,5l (i think that's the A340-600) to round about 9,5l (Avro) (that's liters of course, don't know how much that is in gallons).
so if you know much your car consumes, you can see when which transport mode is more efficient.
don't know about trains, sorry.
If only pure sweetness was offered, why's this bitter taste left in my mouth.