Pennsylvania Dept. of Transportation inspectors are evaluating scrapes on the underside of a highway overpass that partially collapsed Dec. 27 outside Pittsburgh, dropping a section onto Interstate 70 and injuring five motorists. Officials are investigating whether the scrapes are evidence that trucks contacting the underside of the 45-year-old bridge contributed to the failure.

The dropped section, consisting mostly of concrete guardrail and part of the deck, weighed about 80 tons, says Jeff Ofsanik, a PennDOT district spokesman. The place where the deck section failed is its lowest point above the Interstate, 14 ft, 11 in., says another PennDOT spokes person.

Trucks in the area are limited to heights of 13 ft, 6 in. Larger trucks would require a special permit.

Two vehicles struck the collapsed section. A woman and her two small children suffered minor injuries when their minivan crashed into the dropped span and a second car was damaged and two people in it were cut by broken glass when pieces of the falling concrete hit their car, say state police.

State officials closed a three-mile stretch of I-70 in both directions for most of Dec. 28 for debris removal and repair. About 33,000 vehicles travel that section of Interstate each day, according to PennDOT officials. The overpass serves mostly local traffic of about 500 vehicles a day.

Specifications for an emergency replacement are being prepared, say state transportation officials.

“Just looking at it, [inspectors] could not tell what happened,” Ofsanik says. State officials says the overpass had reached the end of its service life. Among possible causes being evaluated are weather and age-related deterioration along with the possibility that trucks have struck the underside of the bridge repeatedly. “They did see signs of scraping on the underdeck,” Ofsanik says.