Progressing like a rail passenger? (2,5)
I believe the answer is:
in train
I believe this clue is a double definition.
'progressing' is the first definition.
(in train means in progress)
'like a rail passenger?' is the second definition.
(riding in a train)
(Other definitions for in train that I've seen before include "Being dealt with (going by rail!)" , "... properly directed" , "Being on board" , "On the move" , "making progress" .)