Railway Age has a précis of the NTSB preliminary report.
The NTSB preliminary report
This information is preliminary and will be either supplemented or corrected during the course of the investigation. Release date OCT 26, 2021.
On September 25, 2021, about 3:47 p.m. local time, westbound National Railroad Passenger Corporation (Amtrak) train 7 (also known as the Empire Builder) carrying 154 people derailed in a right-hand curve at milepost 1014.57 on the BNSF Railway (BNSF) Hi Line Subdivision near Joplin, Montana. (See figure.) As a result of the derailment, 3 passengers died, and 44 passengers and crew were transported to local hospitals with injuries. Damage was estimated by Amtrak to be over $22 million.
Amtrak train 7 consisted of two locomotives and 10 railcars. Eight of the 10 railcars derailed with four railcars derailing on their sides. In the vicinity of the accident area, BNSF authorizes train movements with a traffic control system. Train movements are coordinated by a BNSF train dispatcher located at the Dispatch Center in Fort Worth, Texas. Train movements on the Hi Line Subdivision are governed by operating rules, special instructions, timetable instructions, and the signal indications of the traffic control system and supplemented with an overlaid positive train control (PTC) system. The maximum allowable speed on this section of track was 79 mph for passenger trains. The PTC system was enabled and operating at the time of the derailment. Preliminary data from the leading locomotive’s event recorder showed that train 7 was traveling between 75 and 78 mph when its emergency brakes were activated. The locomotives and the first two railcars remained on the rail. The weather was clear with no precipitation at the time of the accident.
While on scene, National Transportation Safety Board (NTSB) investigators conducted track and equipment inspections, reviewed signal and train control data logs, obtained data from the lead locomotive’s forward-facing image recorder and event recorder, and conducted interviews. NTSB’s investigation is ongoing. Future investigative activity will focus on track and engineering, equipment, survival factors, and passenger railcar crashworthiness.
Parties to this investigation include the Federal Railroad Administration, Amtrak, BNSF, the Brotherhood of Maintenance-of-Way Employes Division, the International Association of Sheet Metal, Air, Rail and Transportation Workers – Transportation Division, and the Brotherhood of Locomotive Engineers and Trainmen. 
(a) All times in this document are local time unless otherwise noted. (b) Amtrak is a passenger railroad service that provides medium- and long-distance intercity passenger rail service in the contiguous United States and to nine cities in Canada. Train 7 operates from Chicago, Illinois, to Seattle, Washington, with a portion of the train removed at Spokane, Washington, and then continuing to Portland, Oregon, as train 27.
The Brotherhood of Maintenance-of-Way Employes Division spells the word “Employes” in its name with one e. Therefore, we are using that spelling in this report.