By 'traffic film' do you mean ordinary dirt Col72? Black trim can usually be cleaned and smartened with dedicated trim cleaners such as 'Back to Black'. You could try some white spirit or meths first to see if that removes the spots.
Try a clean rag with some white spirit, meths or petrol - gently!. One of those should remove the residue then use a black trim conditioner to make the black plastic look good again. Good luck!