Bella Dinh-Zarr, vice chairwoman of the National Transportation Safety Board, told journalists "it's too early to tell" why the train was traveling at such a fast speed, an estimate that came from preliminary information obtained from an event data recorder in the rear locomotive.
The Amtrak train -- which Dinh-Zarr said was likely carrying some 80 passengers, three crew and two service personnel -- was traveling on a new route for the first time before plunging off a bridge onto a busy highway, leaving at least three people dead.
Federal investigators would be on the scene for a full day Tuesday, she said, kicking off a probe into the incident that would likely last seven to 10 days.
Information obtained from the front locomotive's data recorder, which has been more difficult to access, would potentially lend more insight into the train's exact speed, according to Dinh-Zarr.
Several other carriages of the 14-car train also ended up on the highway, shutting down a key section of the busy artery that connects the greater Seattle metropolitan area to Olympia. All but one car jumped the tracks.
Local officials had warned only weeks ago that the track still might not be safe enough to handle trains at higher speeds.