As far as one can travel with the transport chief (8)
I believe the answer is:
railhead
'as far as one can' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
'travel with the transport chief' is the wordplay.
'travel' becomes 'head' (head is a kind of travel).
'with' is a charade indicator (letters next to each other).
'the transport chief' becomes 'rail' (I am not sure about this - if you are sure you should believe this answer much more).
'head' put after 'rail' is 'RAILHEAD'.
Can you help me to learn more?
(Other definitions for railhead that I've seen before include "end of the line - with 26d" , "Terminal of the track" , "End of the train line" , "You've reached the end of the line here" .)