The UK’s National Army Museum has this rather good photo of The opening of the Khyber railway, 1925. Photograph by Randolph Bezzant Holmes (1888-1973), India, North West Frontier, 1925. NAM Image Number 118645.

The text says:

The Khyber Pass Railway from Jamrud, near Peshawar, to the Afghan border near Landi Kotal was opened on 4 November 1925. Built to allow easier movement of troops to the frontier, the railway climbed more than 1,200 metres (3,900 feet) through 34 tunnels and 92 bridges, and culverts to reach Landi Kotal.