SLATINGTON (AP) - The National Transportation Safety Board completed its investigation into a 2018 Pennsylvania Turnpike crash that killed a truck driver when a tunnel conduit fell and smashed through the windshield at the Lehigh Tunnel.

The NTSB issued two safety regulations for federal highway officials.

The NTSB determined the final probable cause of the crash to be the failure of the conduit’s support system due to longtime corrosion, which resulted in its displacement, the agency said in a release Thursday.

Officials also said the Federal Highway Administration has “insufficient guidance” regarding maintenance and inspection of its tunnels. They say that led to the Pennsylvania Turnpike Commission’s delay in repairing the deficiencies that were previously documented.

The commission said in 2018 it was in the process of awarding a contract to replace the straps when the crash happened Feb. 21 in the Lehigh Tunnel.

Thursday’s report said that less than a week before the trucker was killed, the turnpike had hired a contractor to replace its electrical distribution system in the tunnel, a plan that called for moving the metal conduits to a safer part of the tunnel.

A message seeking comment was left with the Pennsylvania Turnpike Commission.

The NTSB said the highway administration must emphasize the “importance of inspecting, documenting and properly repairing significant corrosion in nonstructural elements above roadways” and its manual on maintenance and inspection must be revised.

New Jersey truck driver Howard Sexton III was about a quarter way through the tunnel when he struck a 10-foot section of conduit that had come loose. It penetrated his windshield and struck him in the head. Other vehicles were damaged but the 70-year-old driver was the only fatality.

The conduit came loose in the southbound tunnel, a 4,500-foot tube that opened in November 1991.

Carl DeFebo, dDirector of public relations & marketing for the turnpike, said the Lehigh Tunnel’s southbound tube is the only tunnel in the system in which electrical conduit is directly above drivers.

In older tunnels, the pipes are located with ventilation equipment in a parallel utility tunnel above the roadway.

The vehicle continued to travel south for about 1 mile before coming to final rest on the right shoulder, where Sexton was discovered by Turnpike Safety and State Police at Pocono deceased behind the wheel.

DeFebo said, “The Lehigh Tunnel, like all turnpike tunnels, is subject to a biennial inspection.”

The most recent inspection had been September 2016.

In December 2017, DeFebo said the commission advertised for bids for replacement of the lighting systems in both Lehigh tubes.

A contract was scheduled to be awarded to the lowest responsible bidder at the March 6 Turnpike Commission meeting.

The Lehigh Tunnel construction began with the Northeast Extension in 1956.

Originally the Lehigh Tunnel consisted of the northbound only tube. While this was sufficient in the early years of the turnpike, increasing traffic demands and tourism in northeast Pennsylvania caused the Lehigh Tunnel to become a chokepoint, with traffic reducing from four to two lanes, according to PaHighways.com.

In 1989, work began to double the capacity with the construction of a new southbound only tube, with the original tube serving northbound.

The Times News archives were used in this report.