DETROIT (Reuters) - Union Pacific Corp said on Wednesday it should begin cleanup operations at two rail freight yards in Houston on Wednesday or Thursday but warned that areas east of the city are “still inaccessible at this time.”

The No. 1 U.S. railroad said that it was using helicopters and drones to inspect areas by air that cannot yet be accessed by road.

“As weather and access to storm-damaged areas allow, we are inspecting and repairing track, bridges and signals to return to service as quickly and safely as possible,” the company said in a announcement posted for customers on its website.