The 47-year-old woman, whose name was not released, was walking alone on tracks near the West River railroad bridge when she was hit by the side of a southbound train.
Medics treated the woman near a bridge abutment before she was transported to Brattleboro Memorial Hospital. She later was flown to Dartmouth-Hitchcock Medical Center in Lebanon, N.H.
In the immediate aftermath of the accident, "she was conscious and speaking to us," Brattleboro police Sgt. Mark Carignan said.
Police were called to the scene - at the point where the West River meets the Connecticut River just off Putney Road - at 12:25 p.m.
Initial reports indicated that the woman had fallen into the water.
That turned out to not be the case. Responders found the woman lying near an abutment, with the train stopped a short distance down the tracks.
The train was held for less than an hour while police investigated. Putney Road remained open.
Both Brattleboro and Amtrak police are continuing to investigate. Brattleboro police interviewed train operators and witnesses at the scene.
It was not clear why the woman was on the tracks. Carignan issued a reminder that train tracks are private property.
"Being on the tracks is trespassing," he said at the scene. "We would absolutely recommend that people stay off the tracks. Don't cross the tracks.
On Friday afternoon, Amtrak spokesman Cliff Cole said it was too early to comment on any details of the incident.
Tracks throughout much of Vermont recently were upgraded to allow trains to attain higher speeds. At a ceremony in Brattleboro last year, officials said those changes would allow Amtrak's Vermonter to reach 79 mph.
Cole said walking on tracks is dangerous no matter a train's speed.
"The trains have very little ability to stop quickly if they should encounter a trespasser," Cole said. "And the engineer's first responsibility is to the passengers."
He added that there is little chance for those caught in the path of a moving train to emerge unscathed.
"Anytime anybody sees fit to trespass on the tracks, it oftentimes ends in tragic situations," Cole said. "We try to educate young and old alike ... to just stay off the property."
Mike Faher can be reached at firstname.lastname@example.org or 802-254-2311, ext. 275.