Mackenzie Mellor, 23, was driving with 57-year-old Christopher Mellor in a BMW Z3 on Whams Road, Crow Edge, at about 6pm on March 1 when he lost control of the car on a downhill left-hand bend.
The two-seat car, which was picked up on CCTV travelling towards Barnsley from Brockholes, where the pair lived, was not speeding on the 60mph road, according to police investigators.
The BMW collided with a Mitsubishi Outlander being driven by Emma Rathbone, a doctor who was travelling alone on her way home to Holmfirth.
“I saw the car, which was coming towards me, zig-zagging and it was entirely out of control,” she told the inquest, which was held in Sheffield yesterday.
“I instinctively braked but I just knew we were about to collide. It hit the front of my car, and the airbags deployed. I sustained minor injuries but it was more a case of shock.”
Toxicology reports revealed Mackenzie had ‘cannabis intoxication’, although it was not revealed how much was in his system or if it affected his ability to drive.
A post-mortem said the pair died of multiple traumas, while the family questioned the BMW’s brakes - which had been recently changed - and if that had had an effect.
Michael Orchard, who investigated the crash and inspected the vehicle, added: “I attended the scene at approximately 7.45pm in order to ascertain the likely series of events which led to the collision.
“Shortly after the left-hand bend, there was a kerb mark, followed by tyre marks which continued about 100 metres past the corner’s exit.
“I checked the BMW’s seatbelts, which were both being used at the time of the impact, but the front end was virtually destroyed so I could not tell if the traction control or headlights were on.
“There was no prior existing damage found, but upon receiving more information about the brake change I had a more in-depth look at those.
“The callipers, pads and fluid were all new, but everything was fitted correctly. I took a sample of the fluid to see if any contaminants had affected it, but it passed the manufacturer’s recommendation.
“The driver, upon losing control, attempted to regain the vehicle and effectively tried to steer his way out of the problem, but unfortunately it was too late.”
Coroner Abigail Combes recorded two verdicts of accidental deaths in her conclusion.
“I’m satisfied that on the balance of probability, the evidence is clear that there wasn’t a defect on the vehicle in which Mackenzie and Christopher were travelling in which caused or contributed to it.
“It could be that there was a distraction or simply that an error was made, before the vehicle struck the kerb.
“Mackenzie lost control but took action in an attempt to rectify it, although he was unable to regain the vehicle’s direction. We will never know what caused the incident.”
Christopher’s ex-wife and Mackenzie’s mother, Rachael, set up a Just Giving page in aid of the Yorkshire Air Ambulance, which landed on the road and transported the pair to hospital.
A total of £3,945 was raised and a statement on behalf of the family said: “Mac and his dad, Christopher, were tragically killed in the car accident. We would like to thank the Yorkshire Air Ambulance for coming to help and all the other people they help as part of their everyday work. Our lives are changed forever.”
Click here to donate.