SATSUMA — A tractor-trailer truck traveling on Interstate 12 early Wednesday in Livingston Parish hit a bridge rail and blocked traffic after the driver died behind the wheel, State Police reported.

Investigators said the driver, whose name was withheld until relatives are notified, apparently died of natural causes around 2 a.m., troopers said in a news release.

A preliminary investigation revealed the 2005 Peterbilt rig was headed east on I-12 at a point east of Satsuma when the rig went out of control, the release said.

The truck drifted to the left and hit a bridge rail before coming to rest and blocking the inside lane of travel, the release said.

Because there was no braking or steering input before the crash occurred, troopers suspect the driver was stricken before the 18-wheeler hit the bridge rail, the release said.

The Livingston Parish Coroner’s Office pronounced the driver dead at the scene.