Melted tarmac runs under vehicle (7)
I believe the answer is:
tramcar
'vehicle' is the definition.
(tramcar is a kind of vehicle)
'melted tarmac runs under' is the wordplay.
'melted' is an anagram indicator.
'runs' becomes 'r' (cricket abbreviation).
'under' is a charade indicator (letters next to each other).
'tarmac' is an anagram of 'tramca'.
'tramca'+'r'='TRAMCAR'
(Other definitions for tramcar that I've seen before include "Public street transport on rails" , "Electric transport" , "Passenger vehicle running on rails" , "Electrical vehicle" , "Electrically driven public transport vehicle" .)