(AP) -- Nearly 11 months after a Metro-North derailment killed four people in the Bronx, federal regulators are sharing their conclusions about what caused the riverside wreck.

The National Transportation Safety Board said it would announce "probable causes" Tuesday for the Dec. 1 derailment and four other Metro-North accidents in New York and Connecticut that occurred within 11 months in 2013 and 2014.

Sen. Richard Blumenthal, D-Conn., who has seen the report and will be at a Grand Central Terminal news conference, said Monday, "It will document the cascading catastrophes over a single year illustrating the urgent need for dramatic upgrades and improvements in safety and reliability."

The board has issued hundreds of pages of findings from its investigations, but until now has emphasized that no cause had been established.

It reported in April, for example, that the engineer of the derailed train, William Rockefeller, suffered from undiagnosed sleep apnea, which interrupted his sleep dozens of times each night. Investigators said Rockefeller told them he felt strangely "dazed" right before the crash.

The train came off the tracks as it hit a curve along the Hudson River that carries a 30 mph speed limit. The NTSB said the train was going 82 mph.

More than 70 people were injured. Three of the four victims were from the Hudson Valley.

When investigators asked Rockefeller if he was clearheaded enough to realize he was hitting a curve, he said, "apparently not."

The other accidents include:

--A derailment and collision in Bridgeport, Connecticut, that injured more than 50 people on May 17, 2013.

--The death of a track foreman who was hit by a train in West Haven, Connecticut, on May 28, 2013.

--The derailment of a freight train on Metro-North tracks in the Bronx on July 18, 2013. There were no injuries.

--The death of a Metro-North electrician who was hit by a train in Manhattan on March 10, 2014.

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.