The Kalka–Shimla Railway runs between Kalka and Shimla. The railroad is a 95.66 kilometers (59.44 mi) long, 2 ft 6 in (762 mm) narrow-gauge line. Shimla is the modern capital of Himachal Pradesh and is located at an elevation of 2,205 meters (7,234 ft) in the foothills of the Himalayas. It was formerly the summer capital of British India, starting in 1864, and also served as the headquarters of the British Army in India.
Prior to construction of the railroad, the only access to Shimla was by village cart-way. The railway line was constructed by the Delhi–Ambala–Kalka Railway Company, beginning in 1898 in the Siwalik Hills, and was completed in 1903.
The Kalka–Shimla Railway has 103 tunnels and 864 bridges. Many of the bridges are multi-arched, reminiscent of Ancient Roman aqueducts, while one bridge, which spans 18.29 meters (60.0 ft), is made with plate girders and steel trusses. The ruling gradient of the railway is 1:33 or 3%, and it features 919 curves, with the sharpest at 48 degrees (a radius of 37.47 meters (122.9 ft)). The tracks climb from 656 meters (2,152 ft) to a peak elevation of 2,076 meters (6,811 ft) at Shimla. The longest tunnel on the line is the Barog Tunnel (No. 33), which is 1,144 meters (3,753 ft) long, connecting Dagshai and Solan. The loops at Taksal, Gumman, and Dharampur help to attain flatter gradients.
The Kalka–Shimla Railway joined the Nilgiri and Darjeeling lines as a World Heritage Site in 2008.