Cheap fare starts to get rail users back on the line (5)
I believe the answer is:
gruel
'cheap fare' is the definition.
(I've seen this before)
'starts to get rail users back on the line' is the wordplay.
'starts to' suggests taking the first letters.
'back on' says to take the final letters (the letter at the back).
'line' becomes 'l'.
The initial letters of 'get rail users' is 'gru'.
The last letter of 'the' is 'e'.
'gru'+'e'+'l'='GRUEL'
(Other definitions for gruel that I've seen before include "Unappetising food" , "Thin porridge" , "disappointing fare" , "Thin oatmeal dish" , "Thin soup" .)