From Longman Dictionary of Contemporary Englishtraffic copˈtraffic cop noun [countable] informal 1 SCPa police officer who stands in the road and directs traffic2 a police officer who stops people who are driving in an illegal way
Examples from the Corpus
traffic cop• As the reader might expect, I had my hands full acting like a traffic cop.• Silicon Valley also is playing a major role in policing the Internet jam, like a traffic cop in downtown San Francisco. 