​​On August 20, 2012, about 11:54 p.m. eastern daylight time, an eastbound CSX Transportation (CSXT) coal train, U81318, derailed the first 21 cars at milepost (MP) 12.9 while crossing the railroad bridge over Main Street on the Old Main Line (OML) Subdivision in Ellicott City, Maryland. The train consisted of two locomotives and 80 loaded coal cars; the train length was 4,227 feet and the weight was 9,873 trailing tons. Seven of the derailed cars fell into a public parking area that was below and north of the tracks. The remainder of the derailed cars overturned and spilled coal along the north side of the tracks.

Prior to the train crossing the bridge, two individuals entered the railroad right-of-way on the north side of the railroad bridge that crossed Main Street. They climbed over a short wooden fence and entered CSXT property without authorization to access the railroad bridge. They were sitting on the bridge during the derailment. Both individuals were killed by the spilled coal.

The CSXT train crew consisted of an engineer, a conductor, and an engineer trainee. No crewmembers were injured. At the time of the accident, the sky was cloudy and dark, the wind was calm, and the temperature was 65°F. The damage was estimated to be $1.9 million.

The CSXT train crew reported for duty at 4:00 p.m. on August 20, 2012, in Cumberland, Maryland. The train departed Cumberland eastbound toward Baltimore, Maryland.​

We determined that the probable cause of the Ellicott City derailment was a broken rail stemming from an undetected internal defect which grew to a catastrophic failure due to the combination of a worn rail head that was approaching levels for scheduled replacement and high axle loads.​