Why trains derail

From NBC:

Exclusive video obtained by the I-Team shows MTA workers cleaning up dangerous, unsecured rail equipment Thursday, after an I-Team report on Wednesday identified multiple subway lines with loose spare parts scattered on their tracks.

So how exactly did this happen?

From the Daily News:

A Long Island Rail Road train sideswiped another train in Queens, Friday, causing massive delays that left thousands of rush hour straphangers stranded, officials said.

Investigators are trying to determine if one of the trains slightly derailed before scraping against the train just outside the Jamaica station at 6:30 p.m.

No injuries were reported, according to an LIRR spokesman.

F train derails in Woodside

From CBS:

A Brooklyn-bound F train derailed Friday morning in Woodside, Queens.
The derailment happened at around 10:40 a.m. in a tunnel at 65th and Broadway.
The MTA reports the train was on the express tracks.
The FDNY is using access points to get to the subway and bring stretchers to the train.
There have been several minor injuries, according to CBS 2′s Kathryn Brown.