A 63-year-old man was killed in a single car collision in Williamson County on Tuesday night. The accident occurred on Holly Tree Gap Road just after 8:30 p.m.According to authorities, William Steele III was traveling northbound on the roadway when his 1998 Aston Martin went off the right shoulder of the road, striking a utility pole. The vehicle then rolled over before coming to a rest at the bottom of a ditch. Steele was the only occupant inside the vehicle. Authorities said he was wearing his seat belt at the time of the crash.