Leonard-Wheeler pulled over and went to check on the male driver, alongside other concerned motorists and bystanders.
Bystanders managed to get his door open and put him in the recovery position outside, and started to perform CPR.
Emergency services arrived soon after and paramedics unsuccessfully tried to resuscitate him.
Police said the matter had been referred to the coroner.
Earlier this week, investigators were seeking information from witnesses who had seen the small green Toyota hatchback in the lead-up to the crash, and encouraged people with information to call 105 and reference event number P055371468.