Chugging its way through history all the way to achieving a Unesco World Heritage tag, the British-era narrow gauge Kalka-Shimla rail track is facing threats - all of them man-made.
The massive cutting of the highly fragile mountain for four-laning the National Highway between Parwanoo and Solan towns in Himachal Pradesh has posed a threat to the rail track that was opened by Lord Curzon, the Viceroy of India in 1903.
Experts and locals say the maximum threat to the rail track is on a 30-km stretch between Parwanoo and Kumarhatti where frequent landslides and sinking of mountains due to soil erosion and loss of vegetation are high.
The hill slope is critical while building a road in the mountains but for the four laning of the 88-km stretch that connects Shimla and Parwanoo, the hills have been or are being cut vertically at most places, making the mountain ecosystem fragile, a railway official told IANS.
Geologists blame unscientific cutting of precipitous hills, largely of shell, sandstone and clay, for the frequent landslips.
"Most of these mountain slopes are of sedimentary formation and have become destabilised with the reckless cutting by heavy earth-moving machinery. The loose and naked boulders with muck will continue to roll down on the highway for eight to 10 years more," former state geologist Arun Sharma told IANS.
"On the Parwanoo to Solan stretch, most of the hill cutting was done largely vertically than horizontally. At some points, large-scale vertical cutting was carried out," added Sharma, a member of the Environment Ministry's State Expert Appraisal Committee to assess projects.
Some of the stretches along the Parwanoo-Solan stretch have become permanent landslide points like Chakki ka Mor. The risk of driving is aggravated after dusk, say motorists.
A staggering 23,785 trees are likely to be cut for the road widening from Parwanoo to Solan, official records say. But the project aims to cut travel time between Chandigarh and Shimla by a mere 17 km.
The executing agency, the National Highway Authority of India (NHAI), says it is aware of the threats and taking mitigating steps.
"We are well aware about possible threats to the rail track with the construction of the National Highway. We are taking all preventive measures to safeguard the track," NHAI project Director Sanwar Mal Swami told IANS.
"We are in regular touch with railway officials and taking cognizance on their advisories," he added.
The construction of the Solan-Parwanoo highway will be completed by March 31, except for the overbridges at Jabli, Kumarhatti and Solan.
Unesco had included the 30-inch gauge Kalka-Shimla rail line in the list of World Heritage Sites in 2008