Motorway madness, it appears! (6)
I believe the answer is:
mirage
'it appears' is the definition.
The definition suggests a singular noun which matches the answer.
'motorway madness' is the wordplay.
'motorway' becomes 'MI' (resembles M1, English motorway).
'madness' becomes 'rage' (synonyms).
'mi'+'rage'='MIRAGE'
Can you help me to learn more?
(Other definitions for mirage that I've seen before include "Something illusory and unattainable" , "French fighter aircraft" , "Hallucination caused by hot air" , "vision" , "Deceptive image, in the desert say" .)