The Pir Panjal Railway Tunnel or Banihal railway tunnel is an 11.215 km (7 mile) railway tunnel located in Pir Panjal Range of middle Himalayas in Jammu and Kashmir, India, north of Banihal town.
It is India’s longest railway tunnel.

The average elevation of the 11.215 km long railway tunnel is 1,760 m (5,770 ft) or about 440 m (1,440 ft) below the existing road tunnel, the Jawahar Tunnel, which is at elevation of about 2,194 m (7,198 ft).The tunnel is 8.40 m wide with a height of 7.39 m. There is a three metre wide road along the length of the tunnel for the maintenance of railway tracks and emergency relief. It takes approximately 9 minutes and 30 seconds for the train to cross the tunnel.

Source: http://en.wikipedia.org/wiki/Pir_Panjal_Railway_Tunnel