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The Arkansas report said it was “highly unlikely” that a similar crack would occur on the bridge, but said the bridge’s welds will continue to be inspected at arm’s length and that ultrasonic testing should be done periodically.

But the latest RAV4 uses a lighter, stronger steel that requires ultrasonic testing.

“The report states that this type of failure would have been undetectable with conventional ultrasonic testing, as it will not pick up a corrosion pit in the base of the rail,” Lavin said.

Metro sent the results of those tests to outside experts for reexamination, and those experts concluded that Metro staff properly interpreted the results of the ultrasonic testing.

Ultrasonic testing on that stretch of track took place in August 2017.