An Arkansas trucker hauling a 30,000-pound load of steel died Wednesday when his rig slammed into a support pier on Interstate 20 at the Wisconsin Avenue overpass.

Mark Lewis Duke, 39, 601 N. Summit, Lot 14, Benton, was westbound at 1:30 p.m. when, for reasons unknown, the truck left the road, Sgt. Jackie Johnson said.

Witnesses driving behind the truck told police Duke did not brake before striking the pier, an impact that shredded the truck beyond recognition and left parts and debris strewn along the highway and onto North Frontage Road.

The overpass was closed to determine if large cracks in the pier were cosmetic or structural.

Westbound traffic crawled for more than four hours as police routed traffic into the left lane, causing a slowdown that still stretched to the Bovina exit, about 10 miles from the scene, four hours after the wreck.

Police declined to speculate if Duke fell asleep at the wheel or suffered an attack of some kind, but suspect one or the other as a cause. He was killed instantly and an autopsy was to be performed today at the Mississippi State Crime Lab in Jackson, Warren County Coroner Larry Chisley said.

When contacted by police, the truck’s owner said Duke was driving three steel plates to Shreveport.

Employees of businesses at 1901 N. Frontage Road described the sound as a &#8220loud kaboom”.

&#8220I’ve never seen an accident like that before in my entire life,” said Lee Baker, an employee of Heads Up Salon And Day Spa, as she and owner Kayla Hinson watched police and Mississippi Department of Transportation crews clean up debris thrown as far as the salon’s parking lot 50 yards away.

John Kendrick, director of Vicksburg Christian School, which is also in the nearby strip mall, said the sound shook his pupils &#8220out of our chairs.”

Cedric MacWilliams was working atop a ladder painting near the front door of the salon at the time.

&#8220I heard the noise, then it got real quiet for some reason. I turned around and just saw smoke and fire.”

Engineers with MDOT will assess the stability of the overpass today, Central District Engineer Walter Lyons said.

&#8220It’s still OK for traffic. We will determine what repairs are needed,” Lyons said, adding there is &#8220a tremendous amount of reinforcement in those beams.”

The wreck was the 12th fatal accident in Warren County in 2006 and the fifth inside Vicksburg.