Traffic controller with knotted rope traps European (5,4)

'traffic controller' is the definition.
(type of road marking)

'with knotted rope traps european' is the wordplay.
'knotted' indicates anagramming the letters.
'rope' becomes 'line' (I've seen this in other clues).
'traps' indicates putting letters inside.
'european' becomes 'e' (abbreviation e.g. EU).
'with' anagrammed gives 'whit'.
'whit'+'line'='whitline'
'whitline' enclosing 'e' is 'WHITE LINE'.