be on traffic duty

Perhaps he had been on traffic duty at the time?

We don't put someone who's just been on traffic duty to work on that cyber-crime."

Officer Behrle writes an average of four or five tickets an hour during the time he is on traffic duty, and the average fine is more than $100.

The first officers arrived seven minutes later, soon followed by PC Keith Simmonds of Oxted station who was on traffic duty that night and who saved the injured baby from the wrecked house.