“There’s no such thing as a routine traffic stop” is a police adage. Police don’t know the type of person they are pulling over and have to prepare for the unexpected.
 
“There’s rarely any such thing as a routine traffic stop any more where young people are involved” was printed in the Los Angeles (CA) Times on July 13, 1969. “I don’t think there is any such thing as a routine traffic stop anymore” was printed in The Fresno Bee/The Republican (Fresno, CA) on September 18, 1970. “There is no such thing as a “routine” traffic stop” was printed in the book Police Traffic Control (1971) by V. A. Leonard.
 
           
Newspapers.com
13 July 1969, Los Angeles (CA) Times, “The New Drug Tempo: Younger Users, More Arrests” by David Shaw, sec. J, pg. 4, col. 2:
“There’s rarely any such thing as a routine traffic stop any more where young people are involved. We’re too aware of the drug problem.”
(Spoken by an unnamed narcotics officer.—ed.)
 
Newspapers.com
18 September 1970, The Fresno Bee/The Republican (Fresno, CA), “Gun At Head Clinches It: No Stop Is Routine” by Gerald Merrell, pg. 1-C, cols. 4-5:
“I (Warren Gatrell of the California Highway Patrol—ed.) don’t think there is any such thing as a routine traffic stop anymore.” 
 
Google Books
Police Traffic Control
By V. A. Leonard
Springfield, IL: Thomas
1971
Pg. 51:
There is no such thing as a “routine” traffic stop. Every violator contact should be approached with caution and with the full knowledge that anything can happen. Human behavior is unpredictable at the moment, either as an emotional response, or as a result of the violator feeling that he cannot afford the search or run the risk of being taken into custody.
   
Newspapers.com
28 December 1975, Today (Cocoa, FL), “No Stop BY Police ‘Routine’” by Robert Rothman, pg. 2B, col. 2:
“I don’t think there’s any such thing as a routine traffic stop,” Sands said.
(Harry Sands of the Titusville Police Department.—ed.)
 
Google Books
Midnights:
A Year with the Wellfleet Police
By Alec Wilkinson
New York, NY: Random House
1982
Pg. 76:
You stop a car for speeding, it could be a routine thing, although they always say there is no such thing as a routine traffic stop, but say you pull somebody over, speeding, or a taillight out, that car could be stolen, or the person driving it or one of the passengers could be wanted somewhere.
   
Google Books
The Public and the Police:
A Partnership in Protection
By Earl M. Sweeney
Springfield, IL: C.C. Thomas
1982
Pg. 29:
Officer Survival
Because of the possibility of unwittingly stopping a wanted person or someone who has just committed a serious felony, there is no such thing as a “routine traffic stop.” 
 
Google Books
Law Enforcement Patrol Operations:
Police Systems and Practices
By Larry D. Nichols
Berkeley, CA: McCutchan Pub. Corp.
1990
Pg. 273:
THE “ROUTINE” TRAFFIC STOP
There is no such thing as a routine traffic stop! Any traffic stop, either for a traffic violation (including alcohol violations) or a suspected felony, represents great risk to the law enforcement officer.
 
Google Groups: misc.emerg-services
A lesson: Be a sop with a cop
Ralph E. Nelson
5/28/92
(...)
As far as police officers are concerned, there is no such thing as a “routine” traffic stop.  Every stop has the potential for danger.
 
Google Books
An Introduction to Policing
Seventh Edition
By John S. Dempsey and Linda S. Forst
Delmar Cengage Learning
2012
Pg. 397:
Police Traffic Stops
There is no such thing as a “routine traffic stop” for officers, especially for the officer whose primary duty is to make contact with the traffic violator.
   
Google Books
So You Want to Be a Cop:
What Everyone Should Know Before Entering a Law Enforcement Career
By Alley Evola
Lanham, MD: Rowman & Littlefield
2017
Pg. 69:
There is no such thing as a “routine traffic stop.”
 
Traffic stops, generally speaking, involve several unknown elements and can therefore veer wildly from routine. You never know for sure who you are stopping, what criminal activity they may have engaged in recently, or what potentially troubling items are in the car you are stopping.
 
Twitter
Politics Bird
@politicsbird
Replying to
@meauxjo1
I’m torn here.
“There’s no such thing as a routine traffic stop.”
I first heard that in 1968 as a kid. Uncles were on the job #NYPD
Evil exists, I have looked it in the eye. I have no answers for gun violence, any violence….evil.
God bless Law Enforcement
8:36 PM · Aug 31, 2019·Twitter for iPhone
   
NBC 10 News (Providence, RI)
Franklin police capture loose emu
by NBC 10 NEWS Tuesday, October 15th 2019
Franklin police on Monday quoted an old adage, “there’s no such thing as a routine traffic stop.”
 
And officers proved that with the capture of an emu.