Roads are the biggest problems in hill stations. Trains have very little impact on the nature.
A railway line takes up only 3-4 meter wide strip of land. And on hilly routes which have less trains, the tracks are empty most of the day, with only a few trains running in the whole day. And also, other than the railway stations, there are literally no buildings or other structures that come up beside the railways. So, for most of the time, the railway line is no different from the rest of hte forest and animals can move around freely. There will also be very less interaction with humans. Even though many trees are cut down to lay the line, there won't be...
more... any further deforestation afterwards.
On the other hand, roads have constant traffic and there will be dozens of vehicles passing every hour, many of them at high speed. Lots of buildings like shops, hotels etc come up all along the length of the road. Even though the road is only a few meters wide, a wide stretch of land on either side of the road is also taken up by human settlements, which impact the wildlife movement in the area and also increase human-animal conflict. And as the shops increase, more and more trees are cut down, reducing the forest cover.
For these reasons, railways are the best option for giving transport option in forested regions. Large highways and roads with heavy traffic should not be allowed in forested regions and should be replaced with railways, to have minimal impact.