Before, public transport could be hell (6)
I believe the answer is:
erebus
'be hell' is the definition.
(thesaurus)
'before public transport' is the wordplay.
'before' becomes 'ere' (usually literary).
'public transport' becomes 'bus' (bus is a kind of public transport).
'ere'+'bus'='EREBUS'
'could' acts as a link.
(Other definitions for erebus that I've seen before include "Greek god of darkness, son of Chaos" , "In place of darkness" , "The abode of the dead" , "Dark and gloomy cavern between earth and Hades." , "Antarctic volcano; region between earth and Hades" .)