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.