Originally built as a metre-gauge line, the Bolan Pass Railway was re-laid as broad-gauge in the 1890s. It is eighty-six miles long, and the aggregate rise from Sibi, at the foot of the incline, to Kolpur, the summit before reaching Quetta, is 5,463 vertical feet. This great ascent necessitates long stretches graded at 1 in 25 and 1 in 33 throughout both of which the line is double as well as climbs of 1 in 40 on easier gradients.