Hum is a village in the municipality of Trebinje, Republika Srpska, Bosnia and Herzegovina. Between 1901 and 1976, it used to be an important junction on the Gabela - Zelenika narrow gauge railway.
A narrow-gauge railway is a railway with a track gauge narrower than 1,435 mm standard gauge. Most narrow-gauge railways are between 600 mm and 1,067 mm.
Comparison of standard gauge and three foot narrow gauge wheelsets
1556 woodcut from De re metallica, showing a narrow-gauge railway in a mine
An Electric Tilt Train in Queensland. Unlike other states in Australia which use different gauges, Queensland's network is made up of 3 ft 6 in (1,067 mm)-gauge track.
The 3 ft (914 mm) gauge Disneyland Railroad in California