What does the passage suggest the Kalka–Shimla Railway did for mountain people?

Building a railway across flat land is hard enough. Building one up the side of a mountain is a far greater challenge, and three of India's mountain railways are together listed as a single World Heritage Site: the Mountain Railways of India. All three are still running today.

The first and best known is the Darjeeling Himalayan Railway. It opened in 1881 and is still considered the most outstanding example of a hill railway built to carry passengers. Its builders used bold and clever engineering to lay a working line across difficult mountain country of great beauty.

The Nilgiri Mountain Railway, in Tamil Nadu, was first proposed in 1854. The mountains made it so hard to build that work began only in 1891, and the line was finished in 1908. It is a single-track line 46 kilometres long, on metre gauge, and it climbs from 326 metres above sea level to 2,203 metres, using the latest technology of its day.

The third is the Kalka–Shimla Railway, a single-track line 96 kilometres long, built to serve the hill town of Shimla. It stands for the great effort, in skill and in materials, that went into ending the isolation of mountain people by bringing the railway to them.

The three railways were added to the World Heritage List one by one, in 1999, 2005 and 2008.