The University of California report was mentioned on another list so I was
already aware of it. I agree with Ian's conclusions.
I haven't looked through the report, but have the following factors been taken
(a) The network of airports is far less dense than that of rail stations, so an
air based transport system would still need supplementary vehicles to carry
people to/from their nearest airport.
(b) I suspect that the proportion of air travellers who drive to/from the
airport is much greater than the proportion of rail travellers, leading to yet
(c) Trains typically have a much smaller load factor than planes, so there is
more potential for improving their environmental performance by increasing