In its investigation of five Metro-North accidents, the National Transportation Safety Board (NTSB) identified several recurring safety issues, including inadequate and ineffective track inspection and maintenance; extensive deferred maintenance issues; inadequate safety oversight; and deficiencies in passenger car crashworthiness, roadway worker protection procedures and organizational safety culture.

Within an 11-month period from May 2013 through March 2014, the NTSB launched investigations into five significant accidents involving Metro North. Taken together, these accidents resulted in six fatalities and 126 injuries. During the investigations, the NTSB found several safety management problems that were common to all of the accidents.

"Seeing this pattern of safety issues in a single railroad is troubling," said NTSB Acting Chairman Christopher A. Hart. "The NTSB has made numerous recommendations to the railroad and the regulator that could have prevented or mitigated these accidents. But recommendations can only make a difference if the recipients of our recommendations act on them."

The probable causes released on Tuesday are for the following Metro-North accidents:

• May 17, 2013, derailment and subsequent collision in Bridgeport, Conn.

• May 28, 2013, employee fatality in West Haven, Conn.

• July 18, 2013, CSX derailment on Metro-North tracks in Bronx, N.Y.

• December 1, 2013, derailment in the Bronx.

• March 10, 2014, employee fatality in Manhattan.

As a result of the early findings from the five investigations, the NTSB initiated an in-depth special investigation of the Metro-North Railroad. On November 19, the board will hold a meeting to discuss the numerous safety issues identified during that special investigation. During the meeting, investigators will discuss all five Metro-North accidents, examine the common elements that were found in each, and highlight lessons learned and the steps that have been taken to make rail transit safer for Metro-North passengers.

The NTSB will also issue safety recommendations designed to improve railroad safety on Metro-North and other railroads. Early this year, the NTSB made safety recommendations to the Federal Railroad Administration and to Metro-North that address some ongoing issues.