Buses, subways, and trains allow passengers to stand up as they travel. This clearly improves the packing potential, and allows a greater capacity of passengers per trip, thus increasing energy efficiency.
The NY Times thought that Airbus had considered doing this at some time. The paper eventually retracted the story as no one could find firm evidence as to the validity of the assertion.
Hilarity ensues when some right-wingers mock and debunk the innocuous NY Times reportage, all the while lying and then trying to cover up their own wild-eyed assertions. They don't succeed however, as ordinary blokes can record the lies for posterity.