The fatal Amtrak crash south of Seattle occurred on tracks where equipment for automatic braking, which Congress has required on all railroads by the end of 2018, was installed but was still being tested.

Train 501 was going 80 mph Monday in a curve posted for 30 mph when several cars derailed and dangled off a bridge above Interstate 5, according to Bella Dinh-Zarr, a member of the National Transportation Safety Board that is investigating.

At least three people died and dozens were injured when 13 train cars jumped the tracks during the train's inaugural run along a new bypass route. The train carried 85 passengers and crew members.

The board will spend months determining what role speed and any other factors played in the accident before making recommendations about how to avoid future accidents.

Washington Governor Jay Inslee vowed at a press conference Tuesday to get to the bottom of what caused the crash. He said while the cause remains unclear, he knows there will be lessons learned and changes made for the future.

“Given the nature of nature of this tragedy and given the extent of loss, I feel we will succeed in improving rail transit out of this,” he said.

He also said President Donald Trump was “jumping to conclusions” when he posted on Twitter that the crash showed why his upcoming infrastructure plan to fix crumbling bridges, tunnels and railways was needed.

“We don’t know at the moment whether infrastructure, meaning the rail bed or the bridge, played any role in this accident at the moment,” Inslee said. “We simply don’t know that, so I would say that was perhaps jumping to conclusions before the investigation has been completed. The president did not follow my advice, which is let’s not jump to conclusions before we make decisions.”

Congress set the deadline for railroads to install automatic braking after a collision in Chatsworth, Calif., in 2008 between a commuter train and a freight train killed 25 people. Safety advocates contend the technology could have prevented the accident.

The technology collectively known as “Positive Train Control” provides signals between tracks, trains and dispatch centers to slow down speeding trains or to stop them at the appropriate signals if the engineer isn’t responding. Railroads are installing the technology piecemeal across the country at a cost of billions of dollars.

"The Positive Train Control equipment has been installed and is now still in testing, which is why the system has not been activated," Jason Abrams, an Amtrak spokesman, said of the track owned by a Seattle-area transit company where the accident occurred.

Sound Transit owns the tracks south from Tacoma to Dupont, where the accident occurred, providing its own transit service as far south as Lakewood, according to spokesman Geoff Patrick.

But the state Department of Transportation upgraded the tracks with federal funding so Amtrak could travel farther south along the tracks, while avoiding freight tracks that run along the shore of Puget Sound.

“We own the tracks, but we do not operate on them,” Patrick said of the accident location.

Sound Transit has installed Positive Train Control equipment along the railroad right-of-way, which will communicate with trains and network control centers, Patrick said. But the system hasn’t yet been linked together or certified as operational, he said.

“We are well ahead of the December 2018 deadline and on schedule for implementing in the second quarter of 2018,” Patrick said. “We’re pleased to be well ahead of the deadline.”

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Amtrak CEO Richard Anderson said Amtrak is behind the new technology. “As far as Positive Train Control goes, we are huge supporters of Positive Train Control at Amtrak,” Anderson said.

Keith Millhouse, rail-safety consultant and a former board chairman of Metrolink at the time of the Chatsworth collision, has advocated for Positive Train Control because rail accidents often result from human errors such as distraction that could be avoided with automatic braking.

“The big tragedy here is that if indeed it was over-speed, positive train control would have prevented this accident,” Millhouse said.

He said the accident was “eerily similar” to the fatal Amtrak derailment in Philadelphia in May 2015, which killed eight people and injured hundreds.

The NTSB ruled that the engineer lost awareness of where he was on his route and headed into a 50-mph curve at more than 100 mph. Positive Train Control hadn’t been installed on that part of track by the time of the accident, but Amtrak completed it along its portion of the Northeast Corridor in December 2015.

Benedict Morelli, a New York lawyer who represented passengers in the crash, said Congress should have hastened the requirement for railroads to adopt the technology before the latest accident.

“I worry when I get on an airplane. Before I represented these people, I didn’t get on an Amtrak train and think, ‘God, I hope I don’t derail,’” Morelli said. “Now it’s happening and happening and happening. It just doesn’t make any sense.”

Even when completed, the system is not foolproof.

An Amtrak train struck a backhoe at 99 mph outside Philadelphia in April 2016, killing two people and injuring 36 — despite automatic braking being installed along the track.

In a safety lapse between work shifts, the board found a night foreman lifted a closure on the track, which the day foreman didn’t resume, even though the backhoe remained on the track.

Anderson refused to speculate about what caused Monday’s crash. But he said Amtrak listens to NTSB guidance and is making investments based on recommendations from previous accidents.

“We take those very seriously and continue to make the investments recommended by the NTSB,” Anderson said. “Safety is the highest priority of the Amtrak board.”