Factbox: New York City transit crises in the 21st century

(Reuters) - New York City commuters are braced for the start of a "summer of hell" when extensive track repairs at Pennsylvania Station begin on Monday, forcing a partial shutdown at the busiest train hub in the United States for at least eight weeks.

The work, due to run through Sept. 1, will reduce the number of train platforms available for arrivals and departures, limiting service and causing delays at a facility that has been plagued by operating woes.
Many of the 600,000 commuters who arrive at the station each morning from New Jersey and Long Island will have to scramble for alternative ways into the city.
Penn Station's partial closure is not the first time that New York City has faced a commuting crisis. Here is a list of some of the worst chapters in the recent history of the city's mass transit system.

Superstorm Sandy, October 2012
The Metropolitan Transportation Authority, the subway system's operator, shut down all subway and commuter rail services for 67 hours when Superstorm Sandy made landfall in New York City in October 2012. Limited subway service resumed after 83 hours. The MTA estimated that Sandy caused $4.8 billion of infrastructure damage on the New York City transit system, including severe flooding at the newly rebuilt South Ferry station in lower Manhattan. The station remained closed until June 2017.

World Trade Center attack, Sept. 11, 2001
The attack on the WTC and the destruction of its landmark twin towers resulted in a total shutdown of the New York City subway system for about two hours. Many stations in lower Manhattan remained shut for months. The MTA estimated the cost of infrastructure repair at $855 million.

Transit Strike, December 2005
A strike by the Transport Workers Union in December 2005 caused a three-day shutdown in the city's subway system. The city's economy suffered $400 million in losses each day of the walkout, and the MTA reported revenue dropped $27.3 million that month.

Power blackout, August 2003
New York City subway service was interrupted for 36 hours in August 2003 during the largest power failure in U.S. history. The MTA reported a loss in passenger revenue of $9.8 million.

(In sixth paragraph, corrects year of World Trade Center attack to 2001 from 2011)

(Reporting by Gabriella Borter in New York; Editing by Frank McGurty and Cynthia Osterman)