(Seattle, WA)  --  The National Transportation Safety Board is continuing to investigate an Amtrak train derailment that killed at least three people and injured dozens in Washington state.  Investigators say the Portland-bound Amtrak Cascades train 501 was going 80 miles per hour in a 30-mile-per-hour zone when it derailed and spilled onto I-5 South near DuPont during rush hour traffic yesterday morning.  Preliminary investigations show the fatalities were restricted to passengers on board the train, though several drivers were injured when the train cars crashed onto the freeway.  At least 72 people were taken to hospitals.