William Thomas, 60, was pronounced dead at the scene, officials say.
Suffolk County Police Seventh Squad detectives are investigating an incident where a man died in Manorville.
William Thomas was driving a 2014 Jeep Patriot westbound on the Long Island Expressway, just east of exit 70, when it veered off the road and overturned at approximately 4:50 p.m. Detectives believe Thomas suffered a medical event prior to the crash. A passenger in the Jeep, Catherine Lucero, 55, of Riverhead, was uninjured.
Thomas, 60, of Manorville, was pronounced dead at the scene by a physician assistant from the Office of the Suffolk County Medical Examiner.
The vehicle was impounded for a safety check.