Wichita ? A south-central Kansas railroad bridge that buckled this week while two locomotives and two rail cars were on it passed an inspection last month.

The inspection May 4 showed no defect was found on the century-old bridge over the Chikaskia River near Wellington, according to The Wichita Eagle.

The bridge sagged Tuesday with train cars on it, but there were no injuries reported, said Tom Lange, spokesman for Union Pacific, which owns the bridge and is responsible for conducting safety inspections of all of its bridges. It took about nine hours to clear the stranded locomotives and rail cars from the bridge.

Union Pacific is adding two temporary piers on either side of the failed bridge and hopes to have the line open by Tuesday, Lange said. He said it would take another week to have all repairs made so the temporary piers can be removed and a permanent one put in place.

Lange said erosion from recent rain “caused the bridge to fail.” But the May 4 inspection showed “no issues with the pier or anything else.” The river was five feet above flood stage and was flowing at 32 times its normal rate at noon Monday, according to the U.S. Geological Survey.

Railroad bridge failures are rare; nationally, there were 59 failures from 1982 through 2008, the most recent figures available. Three of those were in Kansas, with the most recent occurring in June 1995.

The Federal Railroad Administration is responsible for overseeing the inspection of the nation’s 76,000 railroad bridges, but the actual inspection is done by the railroad companies that own the bridges.

Bridges are required to be inspected at least once a year, more frequently if traffic is heavy. The failed bridge in Sumner County is inspected twice annually, Lange said.

As part of bridge inspections, railroads must adhere to safety criteria set up by the federal agency and submit their plans for approval by the railroad administration’s three bridge inspectors.