Absolutely nothing on main road and train back is routine (8)
I believe the answer is:
familiar
'is routine' is the definition.
(routine can mean familiar or ordinary)
'absolutely nothing on main road and train back' is the wordplay.
'absolutely nothing' becomes 'FA' (slang term - sweet Fanny Adams).
'on' means one lot of letters go next to another.
'main road' becomes 'MI' (resembles Ml motorway).
'and' means one lot of letters go next to another.
'train back' becomes 'liar' (I can't justify this - if you can you should give a lot more credence to this answer).
'fa'+'mi'+'liar'='FAMILIAR'
(Other definitions for familiar that I've seen before include "Conversant with the witch's cat?" , "Well known from long association" , "spirit" , "Witch's companion" , "Well-acquainted with a witch's cat" .)