Metro said Saturday that investigators had tentatively determined that a heat kink caused the Green Line derailment Friday in Prince George’s County.
Heat kinks are sections of rail that expand in hot weather until they warp out of alignment with the surrounding track, and in its statement, Metro said such a kink that was the “probable cause” of the derailment.
The agency also released a photo of the warped rails that caused three Metro cars to leave their tracks.
Other factors are also being investigated, the transit agency said.
According to Metro spokesman Dan Stessel, heat kinks are more likely to occur when the air temperature exceeds 95 degrees, as it has done in Washington for much of the last week. In such weather, the temperature of the tracks themselves can climb up to 140 degrees.
The 55 passengers aboard Friday’s derailed train experienced no major injuries, and Metro redirected its scheduled maintenance teams to the task of restoring Green Line service over the weekend. Metro said it expects service to be back to normal in time for Monday’s morning commute.