Cities know the way police respond to mental crisis calls needs to change. But how?

A social worker prepares to roll out with an officer at Denver Police District 5 on December 21, 2017. Denver has been a model for other cities, including Philadelphia, trying to create new ways to respond to emergency calls involving mental illnesses or drug addictions. (AAron Ontiveroz/AAron Ontiveroz/Denver Post via Getty Images)

Philadelphia police officers Kenneth Harper and Jennifer Torres were in their patrol car, sitting at a red light, when a call came in over the 911 radio dispatch.

"This job says 'female complaint in reference to dispute with daughter, suffers from bipolar, infant on location,'" Harper read off the computer near the front seat.