The Khojak tunnel on the way from Quetta to Chaman on the Afghan border was one of the earlier marvels of railway engineering in British India. Opened in 1892, it was 12,870 feet long (2.44 miles/3.92 km) and was the longest rail tunnel in South Asia until the Konkan Railway came along over a century later.
The location of most lines in Baluchistan can be seen here: (Kandahar is a little beyond the border at Chaman).
The story of the alternative routes to Quetta is a long and complicated one and will have to wait till another day. Suffice to say that that the Bolan route involved gradients of 1:25 for several miles which was far more severe than any BG or MG main line anywhere else in undivided India. And double tracks were also used because of the slow speeds although there was little passenger traffic north of Quetta.
You may note a station called Hindubagh on the NG line to Fort Sandeman. As you may guess, it became Muslimbagh while the terminus became Zhob before the line closed around 1990.
You can also see the long lonely line to Zahidan in Iran starting off from Spezand. With luck, it has been running passenger trains twice a month for the last few years.
The southern end of the Khojak tunnel started near Shelabagh station. Note the double line though the tunnel.
And this scene appeared on earlier Pakistani currency notes:
(This note was in circulation from 1976 to 2005.)
A longer article about this tunnel can be seen here:
This site (which became inactive in 2011) contains a number of other articles about Pakistan’s railways by Owais Mughal.
Also see this video of Shelabagh station and the tunnel from 2021: