Updated at 10:08 a.m.

Good morning.

The southbound A train derailment in Manhattan on Tuesday was caused by a piece of rail that was improperly stored on the tracks, officials at the Metropolitan Transportation Authority said late Tuesday.

The cause of the accident appeared to be human error, not a track defect, officials said. The agency is now checking rails across the system to make sure replacement parts are being properly stored.

The accident, which left at least 34 people injured, took place between the 135th Street and 125th Street stations. Two cars jumped the tracks after the emergency brakes were activated, officials said.

Here’s what you might need to know for your morning commute:

• A, B, C and D train service has resumed following emergency repair work at the 125th Street station. Expect delays.