NEW YORK — A sleep-deprived engineer nodded off at the controls of a commuter train just before taking a 30 mile-per-hour curve at 82 miles per hour, causing a derailment last year that killed four people and injured more than 70, federal regulators said Tuesday.
William Rockefeller’s sleepiness was due to a combination of an undiagnosed disorder — sleep apnea — and a drastic shift in his work schedule, the National Transportation Safety Board said. It said the railroad lacked a policy to screen engineers for sleep disorders, which also contributed to the Dec. 1 crash. And it said a system that would have applied the brakes automatically would have prevented the crash.
The board also issued rulings on four other Metro-North accidents that occurred in New York and Connecticut in 2013 and 2014, repeatedly finding fault with the railroad while also noting that conditions have improved.
‘‘We truly take to heart all the issues that have been stated,’’ Metro-North president Joseph Giulietti said. As an example, he said the railroad has begun a test project on engineer sleep apnea that will be expanded.
Asked what had happened to Metro-North in recent years, Giulietti replied: ‘‘Our focus on on-time performance versus our focus on safety.’’
Senator Chuck Schumer of New York said the report revealed ‘‘a horror house of negligence resulting in injury, mayhem, and death.’’
‘‘The last thing that should be on the mind of a commuter on Metro-North is whether they’re going to survive the commute,’’ Senator Chris Murphy of Connecticut said.
NTSB acting chairman Christopher Hart, as well as Schumer and Senator Richard Blumenthal of Connecticut, criticized the Federal Railroad Administration for failing to order railroads to adopt NTSB recommendations, including a sleep-disorder screening suggestion 12 years ago.
The railroad administration is ‘‘much too captive to the industry they are supposed to regulate,’’ Blumenthal said.
A spokesman said the agency would respond later.
The NTSB had reported Rockefeller’s sleep apnea in April, saying tests revealed it interrupted his sleep dozens of times each night. Investigators said Rockefeller told them he had felt strangely ‘‘dazed’’ right before the crash. But until Tuesday, it had refrained from declaring his sleepiness the cause of the crash.
It said that less than two weeks before the crash, Rockefeller had switched from a work day that began in late afternoon to one that began early in the morning. The board said that probably compounded his sleep problem.
It also noted that the technology called positive train control was not in use at the time of the crash. Positive train control, another NTSB recommendation on file, can automatically stop a train if it is exceeding a speed limit.
Metro-North has said it is working to install the technology.
On the other accidents, the NTSB found:
■ A May 17, 2013, derailment and collision in Bridgeport, Conn., was caused by broken joint bars, which are used to join rails of different sizes. At least 65 people were injured. The board said Metro-North had deferred scheduled track maintenance and lacked ‘‘a comprehensive track maintenance program.’’
■ A track foreman who was fatally struck by a train in West Haven, Conn., on May 28, 2013, was probably the victim of a mistake by a student rail traffic controller. The controller misunderstood some instructions and canceled the signals protecting the section of track the man was on, the NTSB said.
■ In a similar accident in Manhattan on March 10, 2014, a worker was killed by a train while trying to reenergize tracks that had been out of service for maintenance. The NTSB blamed the accident on briefings that poorly communicated which part of the track would be safe.
■ The derailment of a freight train on Metro-North tracks in the Bronx on July 18, 2013, which caused no injuries, was caused by deteriorated concrete ties and other problems compounded by deferred maintenance, the NTSB said.
In March, the Federal Railroad Administration issued a stinging report on Metro-North, saying the railroad let safety concerns slip while pushing to keep trains on time. Railroad executives pledged to make safety their top priority.
Metro-North is the second-largest commuter rail line in the country. It carried more than 83.4 million riders between New York City and its suburbs last year.