U.S. Transportation Safety Board Finds Corrosion in Fatal Tunnel Crash

This cross-section of strut 16 from the Lehigh Tunnel shows oxidation and PVC coating disbondment from the metal. The strut and other conduit support system and electrical conduit components were examined by the NTSB’s materials laboratory. NTSB photo by Matthew Fox.

The U.S. National Transportation Safety Board (Washington, DC, USA) (NTSB) recently issued two safety recommendations to the Federal Highway Administration (FHWA) based on the NTSB’s findings in its completed investigation of a fatal crash in the Pennsylvania Turnpike’s Lehigh Tunnel on February 21, 2018.

In a Highway Accident Brief, the NTSB detailed its investigative findings regarding the impact of a broken overhead electrical conduit with a semitractor-trailer in the right lane on the No. 2 tunnel’s southbound side.

The truck was about 1,000 ft (304.8 m) into the 4,379-ft (1,334.7-m) long I-476 tunnel—located in Carbon County, Pennsylvania, USA—when it struck a 10-ft (3.0-m) section of overhead electrical conduit. The support system for the conduit had previously failed, leaving it hanging by electrical wires a little less than 9 ft (2.7 m) above the tunnel’s right lane. The conduit impacted the truck’s windshield and struck the driver.

The semitractor-trailer continued through the tunnel and after exiting, moved left, crossed onto the median, and struck a guardrail. The impact with the guardrail redirected the semitractor-trailer across the southbound lanes and to the right shoulder of the highway, where the truck struck the shoulder guardrail. The semitractor-trailer came to rest along the right shoulder of the highway, about 5,240 ft (1,597.2 m) after striking the conduit. The truck driver died in the crash, while no other injuries or damaged vehicles were reported.

In the probe, NTSB and FHWA investigators examined portions of the conduit and suspension system throughout the tunnel, five days after the crash. Investigators found corroded, fractured, and missing transverse conduit supports at multiple locations. In the area of the crash, nine transverse support struts had failed, for a total collapsed length of about 60 ft (18.3 m). The 10-ft section that impacted the truck windshield was part of the collapsed 60-ft section. Damage to the conduit support system in this section appeared to include both preexisting damage and damage caused by the collision, according to the NTSB.

The NTSB’s materials laboratory examined and analyzed several components of the electrical conduit and its support system. The examination and analysis revealed a compromised polyvinyl chloride (PVC) coating near the anchor rod holes and at cut ends of the support struts. The NTSB says this was likely due to them being cut from longer sections, which disturbed the protective PVC coating.

The general pattern of corrosion at the cut ends indicated either a disbonded PVC coating or no coating at all, which led to accelerated corrosion of exposed metal surfaces. The NTSB concluded that the electrical conduit support system in the Lehigh Tunnel likely failed due to the fracture of extensively corroded PVC-coated steel support struts, which allowed the electrical conduit to drop into the path of the oncoming truck.

In its investigative report, the NTSB notes that, although steps taken before the crash by the Pennsylvania Turnpike Commission (Harrisburg, Pennsylvania, USA) to replace the overhead electrical distribution system were consistent with available guidance, the commission did not sufficiently prioritize repairs to protect public safety.

“The National Tunnel Inspection Standards implemented by the Federal Highway Administration are essential for tunnel safety, and the findings of this crash can be used to improve the guidance the standards provide to tunnel owners,” says Robert Molloy, director of the NTSB’s office of highway safety.

The NTSB determined the probable cause for the crash was a failure of the electrical conduit support system due to long-term corrosion, which resulted in displacement of the electrical conduit into the travel path of the semitractor-trailer. Contributing to the crash was the FHWA’s insufficient guidance regarding tunnel maintenance and inspection, which led to the commission’s delay in repairing previously documented deficiencies in the support system, according to NTSB investigators.

Based upon its investigation, the NTSB issued two safety recommendations to the FHWA. The first seeks a notification by the FHWA to tunnel owners of the circumstances of the Lehigh Tunnel crash, with an emphasis on the importance of inspecting, documenting, and properly repairing significant corrosion in nonstructural elements above roadways.

The second recommendation seeks content revisions to the FHWA’s Tunnel Operations, Maintenance, Inspection, and Evaluation Manual; its Specifications for the National Tunnel Inventory; and its inspection training courses, with emphasis on classifying significant corrosion in nonstructural elements as a critical finding requiring immediate action.

The formal Highway Accident Brief 20-04 and related recommendations can be read in their entirety online. The NTSB’s website also has further background information about this investigation that was previously released.

Source: NTSB, www.ntsb.gov.