SLATINGTON, Pa. - 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, and 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.