The couple obligingly get out of the car while the police run some fake checks on the car.
A police officer asks Katie her name and relationship to the driver and she responds: "Boyfriend."
To which the officer replies: "Look, he's not going to be in too much trouble; well he could be in a bit of a lifetime of trouble, really."
Katie then has her attention turned to Michael who is down on one knee holding a ring box. And he asks her to marry him.
After a few moments a shocked Katie responds: "Yes of course".
Michael told The Advertiser that he took several weeks to plan the perfect proposal.
"An American person did (it) and I saw it on Instagram and I had it at the back of my head," he said.
"I floated the idea with one of my nurses (Caitlin Plunkett) and it turns out her brother is a police officer."
It only took a quick phone call, and the police officers were onboard after getting permission from the SA Police management.
Michael believes the planning that went into it will make a very good story to tell future generations.
"Initially (she was in) lots of shock but afterwards she was just trying to figure out how I did it all because I'm not very organised," he said.
"It's a good story to tell our children.
"The boys did so much work. I can't thank SAPOL enough."
Katie had no idea Michael was planning to propose and said she was genuinely shocked.
"I was quite confused ... I turned around and there he was, it was very, very special," she said.
"I didn't think he would go to that extent and that's why it was such a shock."
The happy couple are planning a December wedding in Adelaide.
