My son moved my car onto the driveway, stopped it with the foot brake with the manual transmission in neutral. The hill assist was activated, so when he got out of the car the brake held long enough for him to get out of the car and walk away before the brake released, about 2 seconds. The car then rolled down the driveway into a tree. This could have been a disaster if the tree wasnât there to stop the driverless vehicle.