Roman with a settled routine in public transport (6)
I believe the answer is:
brutus
'roman' is the definition.
(I know this)
'settled routine in public transport' is the wordplay.
'settled routine' becomes 'rut' (I've seen this before).
'in' is an insertion indicator.
'public transport' becomes 'bus' (bus is a kind of public transport).
'rut' put into 'bus' is 'BRUTUS'.
'with a' acts as a link.
(Other definitions for brutus that I've seen before include ""The noblest Roman of them all"" , "He was last to stab Julius Caesar" , "Conspirator in the murder of Julius Caesar" , "legendary hero" , "An honourable man, said Antony" .)