Like road rage, motorway madness is just an illusion! (6)
I believe the answer is:
mirage
'an illusion' is the definition.
(I've seen this before)
'like road rage motorway madness is just' is the wordplay.
I cannot really understand how this works, but
'road' could be 'mi' and 'mi' is located in the answer.
'madness' could be 'rage' (synonyms) and 'rage' is present in the answer.
This accounts for all the letters.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for mirage that I've seen before include "Illusions in the desert" , "Deceptive image, in the desert say" , "You might see this in desert" , "illusory thing" , "fighter craft" .)