HELENA, Mont.—A preliminary report on an Amtrak train derailment in Montana last month that killed three people and injured dozens more offered no clues about what triggered the accident, but said the train’s emergency brakes were activated and that Amtrak estimated the damage at more than $22 million. However, one attorney whose client is suing Amtrak and BNSF Railway said he wanted to learn more about the crash-worthiness of the train’s observation car and an attorney for a crew member said she reported seeing a 30-foot dip along the railroad, where it appeared the track bed had given way. The National Transportation Safety Board issued its preliminary report Tuesday on the Sept. 25 derailment of the westbound Empire Builder just west of Joplin, in north-central Montana. It was mostly factual, saying there were 154 people on board and that 44 passengers and crew were taken to area hospitals with injuries. …