Dawn Kirk, 46, died after the Vauxhall Corsa being driven by her son Ryan is thought to have skidded on black ice and turned on its side after hitting a ditch on the A701 near Beattock, Dumfriesshire.
The 20-year-old officer with Dumfries and Galloway Police suffered minor injuries, but Mrs Kirk died at the scene.
It emerged Mrs Kirk's husband, Kevin, and her brother Justin Clark are also officers with the force.
News of the tragedy, at Marchbank Woods, was broken to him by fellow officers. A police source said: "Our thoughts are with the family at this difficult time."
Last night, a family friend said: "Dawn and Ryan were going to Glasgow for the day. It's an absolute disaster for the family. Ryan had only been in the police for a few months. His dad is well known in the area."
The area has been hit by fog and ice over the past few days, which may have contributed to the crash.
Ryan and his mother were heading north on Thursday when the car hit a sign and came to rest down an embankment. Ryan was treated at Dumfries and Galloway Royal Infirmary then released.
Two rescue units from Moffat and Lockerbie used cutting equipment to free Mrs Kirk from the car, which landed on the passenger side.
The road was closed for around seven hours following the accident. Dumfries and Galloway Police are appealing for witnesses.