He was one of two officers in a BMW X5 which had stopped on the A92 near Crossgates in Fife at around 1.45pm on Thursday after coming across a broken down car.
One officer began directing traffic while the three females in the car walked to safety.
A car transporter then collided with the police vehicle, causing it to leave the road and come to rest on the grass embankment, while the other officer - aged in his 40s - was still inside.
He was airlifted to Ninewells Hospital in Dundee and one of the women suffered minor injuries in the incident.
The road was closed for nearly nine hours.
Inspector Andy Mather said: "Thankfully neither the officer nor anyone else involved sustained life-threatening injuries.
"However he remains in hospital for observations.
"I want to take this opportunity to thank the public, and colleagues, for their supportive messages and would encourage anyone who may have witnessed this, or was travelling on the A92 at this time and has dashcam footage, to get in touch."
Anyone with information can contact Police Scotland on 101, quoting incident 1746 of February 27.