On the evening of July 18, 2013, a CSX freight train carrying municipal solid waste on tracks of the Hudson Line along the Harlem River Ship Canal in the New York City borough of The Bronx partially derailed between the Marble Hill and Spuyten Duyvil stations.

Commuter rail service by Metro-North Railroad, which owns the line, was suspended for two weekends in order to fully restore normal operations.

After investigating the accident, the National Transportation Safety Board (NTSB) found it had been caused by the track stretching to an excessive gauge at the point of derailment.

A crew of four, an engineer and conductor plus a trainee for those positions, led a consist of two SD40-2 locomotives and 24 flatcars specially modified to carry four large containers of solid waste collected by New York's sanitation department to a landfill in Virginia.

[3] There are generally two tracks along this stretch, both electrified with third rails for Metro-North's electric multiple unit trains serving the stations along the Hudson Line south of Croton-Harmon in Westchester County.

They consist of ribbon rail laid in standard gauge on prestressed concrete ties supported by a bed of crushed trap rock ballast.

Metro-North rates the tracks in this area as Class 2 under Federal Railroad Administration (FRA) guidelines, allowing a passenger speed limit of 30 miles per hour (48 km/h) and a freight speed limit of 15 miles per hour (24 km/h) 10 mph below that allowed by the FRA.

[1] As soon as the accident was reported to it, Metro-North suspended service in the affected area between Marble Hill and Spuyten Duyvil.

Passengers on the #781 train, or already waiting at Marble Hill, were taken back to the Yankee Stadium station south of Highbridge Yard and discharged.

By morning rush hour, the railroad had suspended all service on the Hudson Line south of Yonkers, three stations north of the accident site, until cleanup and repairs could be completed.

In the meantime, it arranged bus service from Yonkers to the Van Cortlandt Park – 242nd Street station, the northern terminus of the New York City Subway's 1 train, which many Hudson Line passengers disembark to at the Marble Hill station to reach jobs on the West Side of Manhattan.

Howard Permut, president of Metro-North, promised riders that normal service would resume by July 22, the next Monday, four days after the accident.

Some riders, particularly those who normally took trains to Grand Central, more convenient to the East Side and Brooklyn, chose to drive in instead or take the day off, giving themselves an unanticipated three-day weekend.

A Poughkeepsie woman interning on Wall Street told The New York Times she did not bother calling her superiors to explain why she was late, since "[t]hey take the train too."

Wheel flange grooves were also evident in some of the ties taken back to Highbridge, suggesting the track had been bending outward under load due to decreased structural support from the fouled ballast.

[1] Upon review of Metro-North's maintenance records, the investigators learned that the track and concrete ties had been installed in 2000.

"[1] More recently, the NTSB noted, following a derailment of a passenger train in Connecticut two months earlier, which had also resulted from a defective and inadequately maintained rail, the railroad had hired Transportation Technology Center, Inc. (TTCI), to evaluate its track maintenance program.

Among the tasks undertaken by TTCI was to survey the entire Metro-North system for areas exhibiting surfacing issues like fouled ballast and poor drainage.

Eventually the ties began to crack in the center and abrade at the ends, and the rails themselves begin to cant outwards, gradually exceeding permitted gauge limits, as the track had in this case.

[1] Four days later, the NTSB issued a press release noting that Metro-North had experienced five major accidents, resulting in four passenger and two worker fatalities (the first in its history), in the space of 10 months.