SLATINGTON, Pa. — Federal investigators said in a report released Tuesday that steel straps holding electrical conduits to the ceiling of a Pennsylvania Turnpike tunnel had corroded before a portion of conduit crashed through the windshield of a truck, killing the driver.

The National Transportation Safety Board issued a preliminary report on the Feb. 21 accident inside the Lehigh Tunnel, about 70 miles (112 kilometers) north of Philadelphia. The report said a 2016 inspection of the tunnel's electrical and fan systems had found the corrosion and that the Pennsylvania Turnpike Commission was in the process of awarding a contract to replace the straps when the accident happened.

Mickleton, New Jersey, truck driver Howard Sexton III, was about a quarter way through the about 4,400-foot long southbound tunnel when he struck a 10-foot section of conduit that had come loose. It penetrated his windshield and struck him in the head.

Lehigh County Coroner Scott Grim described the conduit as a large pipe and said other vehicles were damaged, but the 70-year-old truck driver was the only fatality.

The preliminary report said the contract now specifies that the electrical system will be relocated from the tunnel ceiling to the outside edge of the tunnel walls. The work in the southbound tunnel originally completed in 1991 is estimated to be finished in October.

The report said the NTSB plans to identify a probable cause in its final report along with likely making safety recommendations to attempt to prevent similar crashes.