The Balerno line was a short loop railway in Scotland. It was some 6 miles in length leaving the main Caledonian Edinburgh to Carstairs line at Slateford in Edinburgh. It was built by the Caledonian Railway (CR) mainly to service the many enterprises situated along the upper Water of Leith. However, passenger trains also ran. Most trains terminated at Balerno, though they had to travel to Ravelrig to turn round. Other stations were constructed at Colinton, Juniper Green and Currie. In 1923, with the grouping, the CR amalgamated with several other companies to form the London, Midland and Scottish Railway (LMS) which, following nationalisation in 1947, became part of British Railways.
Several local landowners objected to the building of the railway fearing they would lose some of their land. Others were in favour as they believed it would make the transportation of animals and goods easier. The mill owners were strongly in favour. The Balerno line received final Royal Assent in 1870 and opened in 1874. There were many problems in construction requiring 28 bridges, one long tunnel and many cuttings and embankments. The line followed the Water of Leith, crossing it several times. It was built entirely with manual labour at a final cost of a little over £134,000. It was a single track railway with the only passing place at Currie station. Initially a speed limit of 15 m.p.h. was imposed, this being later raised to 20 m.p.h. A maximum of 18 trucks were allowed.
Four bogie engines were built for the opening which could cope with the steep gradients and curves. This type of engine was normally used in factories and other confined spaces. Special four wheeled carriages were also built. In 1899 12 locomotives were specially built for the line. These became known as Balerno Pugs. From 1934 standard tank engines were gradually brought into service replacing the pug engines. Engine number CR419 was one of those used and is now in the possession of The Scottish Railway Preservation Society having been restored by them in 1971 and again in 2009. Railway enthusiasts were enthralled to see these little trains weaving along in such delightful rural surroundings yet so close to the heart of Edinburgh.