Like road rage, motorway madness in 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 in' is the wordplay.
I cannot quite see how this works, but
'road' could be 'mi' (resembles M1 motorway) and 'mi' is located in the answer.
'madness' could be 'rage' (synonyms) and 'rage' is found within the answer.
This accounts for all the letters.
This explanation may well be incorrect...
'just' acts as a link.
Can you help me to learn more?
(Other definitions for mirage that I've seen before include "Optical illusion, in a desert say" , "Optical illusion caused by atmospheric conditions" , "illusory thing" , "unreal" , "Deceptive image, in the desert say" .)