Authorities say driver error appears to be to blame for sending a tractor trailer off the Chesapeake Bay Bridge-Tunnel.

Thomas Anderson, the bridge and tunnel district's deputy director, said Friday that the driver was weaving through slow-moving traffic. He was trying to pass another truck when his rig went over the span's left side and into the frigid bay.

Driver Joseph Chen was seen standing on the truck as it floated in the bay Thursday. But he was unresponsive and in the water when a Navy helicopter rescued him. The 47-year-old died later.

Anderson said a preliminary police investigation does not point to wind as a factor. Wind speeds were more than 40 mph.

Autopsy results are pending. Police are still searching for the truck's cab on the bay's floor.