A 46-year-old motorcyclist died when he lost control of his vehicle and careered into the path of an oncoming car.
Martyn Talbot died almost instantly after the crash on the A269 at Sidley just days after Christmas last year.
An inquest into his death at Eastbourne this week heard it is still not known what caused the father of two to lose control of his Honda machine on the evening of December 28.
Susan Thomas, a forensic collision investigator for the police, said Mr Talbot, a former IT consultant, could have braked hard to avoid an animal in the road or could simply have been riding too fast.
He had not been drinking and there were no drugs found in his system, the inquest heard.
His motorbike toppled over and with him still onboard, it skidded into the path of a Citroen coming in the opposite direction.
The driver Anntoinette Atkins, who has suffered with PTSD since the crash, was heading to see a friend in Herstmoncuex when the crash happened.
She said, “Something was coming towards me and it was lying in the road heading towards my side of the road and into my car.
“There was nothing I could do. I stamped on the brake hard. It felt like I had run over the rider. I stopped quickly, got out of the car and ran back.
“I am terribly upset that I couldn’t have done more to stop.”
Alan Dennis drove past the scene shortly after the crash as he was on his way to Ninfield from Sidley and alerted the emergency services.
The inquest was told that Mr Talbot, who had been off work with stress and depression, suffered with diabetes and had also been diagnosed with Asperger’s, was a competent rider.
His friend who he visited the day of the accident, Peter Lambert-Gorwyn, said Mr Talbot was a very skilled and experienced motorcyclist, observer for IAM RoadSmart, and a member of the ESAM bike club.
Mr Talbot had two young daughters and previously worked in Eastbourne.
His wife Olga, who he met while they were both working at the East Sussex Disability Association, described him as a one of a kind father, supportive and very caring.