TRACKING THE TROUBLE

On Monday night, crews replaced a section of rail near the 125th St. station that had been flagged by a specialized train that picks up defects.

Two supervisors and a track crew replaced the rail, putting a leftover 13-foot length off steel on the tracks, beneath the path of trains.

Extra rails are routinely tucked away on tracks to save time and avoid the need for crews to lug 1,200-pound rails during urgent repairs.

At 13 feet long, the spare section of rail was too short to be stored on the tracks and was left there without being bolted down and secured. Rails have to be at least 19½ feet long.

Around 9:45 a.m., on Tuesday, just as the subway system was pulling out of the morning rush hour, the spare rail caused two of the eight cars of an A train pulling into the 125th St. station to derail. The train’s emergency braking system kicked in.

Shortly before midnight on Tuesday, MTA Chairman Joe Lhota (photo below) and interim director Ronnie Hakim said the cause of the derailment (above) was “human error” and promise to inspect “every inch of rail” and to make sure

parts are stored correctly.

By 1:30 a.m. Wednesday, two track maintenance supervisors — Jason George and Sean Meriam — were suspended without pay by order of an MTA superintendent.