State-owned rail operator Bane NOR announced its plan after another 17 reindeer died on the track between Trondheim and Bodø, bringing to 127 the number killed in similar circumstances within a week.
Images of the lifeless animals lying in the blood-stained snow have triggered a strong reaction at home and abroad.
Bane NOR said it planned to build 25 kilometres (15 miles) of fence in the area from next year, bringing construction forward from 2019 or 2020.
"The collisions with the animals have affected us," company official Vibeke Aarnes said in a statement.
Four deadly incidents have occurred on the same line since November 22nd, provoking despair among the Sami, a small indigenous community in the north, who notably live off reindeer.
Norway is home to around 250,000 semi-domestic reindeer.
At this time of the year, herders take the reindeer to the winter pastures in search of grazing grounds, a perilous journey as many animals are hit by cars and trains. Some also drown.
"It is not an ordinary job, this is our way of life and the entire culture of the southern Sami is based on deer farming," Ole Henrik Kappfjell, who has lost dozens of members of his herd in train collisions, told NRK radio.
"If we abandon that, we also abandon our culture," he said.
Bane NOR said it has extended the area where its trains would travel at slower speeds and is considering an auto-detection system as well as strengthened dialogue with herders, some of whom tag their animals with tracking devices.
More than 2,000 animals including deer were killed by trains in Norway last year.