The Federal Railroad Administration has ordered a modification of the Metro-North system in light of Sunday's tragic derailment, calling for additional signal system technology that would alert speeding engineers and trigger a train's brakes if the drivers do not slow down.

Though investigators from the National Transportation Safety Board are still trying to determine the official cause of Sunday's derailment, which cost four passengers their lives and injured 70 others, engineer William Rockefeller had been going 82 miles per hour when he hit the curve at Spuyten Duyvil, where the speed limit drops from 70 mph to 30 mph.

Union workers have admitted Rockefeller "basically nodded" off and was unable to hit the brakes before reaching the curve; the feds say additional signal safety features would help prevent engineer error in the future. "Safety is our highest priority, and we must do everything we can to learn from this tragic crash and help prevent future derailments," Transportation Secretary Anthony Foxx said in a statement. "While we assist the National Transportation Safety Board in carrying out its investigation, this Emergency Order will help ensure that other Metro-North trains travel at appropriate, safe speeds."

Until the signal system overhaul is complete, however, the feds have ordered the MTA to have two train operators on or near the engineer's cab at sites where the speed limits drop by more than 20 miles per hour. The MTA says they will comply with the feds' order. "Please be assured that we too recognize the gravity of this incident and are committed to taking all necessary steps to ensure that nothing like this ever happens again on any MTA property," Chairman Thomas Prendergast wrote in a letter to FRA administrator Joseph Szabo yesterday.

In another open letter to Prendergast yesterday, Governor Cuomo similarly urged the MTA to work on installing positive train control as quickly as possible. "[T] the MTA should expedite automated speed control for vulnerable track locations across the Metro-North and Long Island Rail Road systems, including those areas where there is a significant speed change. We all agree this is an appropriate measure," he said. Cuomo also attributed the derailment to human error, asserting that "reports have now made clear that the actions of Engineer William Rockefeller were the initiating cause of this tragic accident."