Travel free to the end of the line (4)
I believe the answer is:
ride
'travel' is the definition.
(eg to ride a bus)
'free to the end of the line' is the wordplay.
'free' becomes 'rid' (to be free of something is to be rid of it).
'to the end of the' indicates one should take the final letters.
The final letter of 'line' is 'e'.
'rid'+'e'='RIDE'
(Other definitions for ride that I've seen before include "Lie at anchor" , "Travel in or be carried on" , "Travel by horse, bus, etc" , "Jaunt" , "spin > lift > pedal" .)