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Scotch gauge was the name given to a 4 ft 6 in (1,372 mm) track gauge, that was adopted by early 19th century railways mainly in the Lanarkshire area of Scotland. It differed from the gauge of 4 ft 8 in (1,422 mm) that was used on some early lines in England. Early railways chose their own gauge, but later in the century interchange of equipment was facilitated by establishing a uniform rail gauge across railways: a so-called 'standard gauge' of 1,435 mm (4 ft 8 1⁄2 in). In the early 1840s standard gauge lines began to be constructed in Scotland, and all the Scotch Gauge lines were eventually converted to standard gauge. Later, tram lines of Tokyo adopted this gauge in 1903.
Scottish railways built to Scotch gauge
A small number of early to mid 19th century passenger railways were built to Scotch gauge, they include:
- The Ardrossan and Johnstone Railway.
-  Length: 10 miles (16 km). Authorised on 20 July 1806 and opened on 6 November 1810;
- The Monkland and Kirkintilloch Railway.
-  Length: 10 miles (16 km). Authorised on 17 May 1824 and opened on 1 October 1826. The engineer was Thomas Grainger.
- The Ballochney Railway.
-  Length: 6.5 miles (10.5 km). Incorporated on 19 May 1826 and opened on 8 August 1828.
- The Edinburgh and Dalkeith Railway.
-  Authorised on 26 May 1826 and opened in part on 4 July 1831.
- The Garnkirk and Glasgow Railway.
-  Length: 8.25 miles (13.3 km). Incorporated on 26 May 1826 and ceremonially opened on 27 September 1831 for both passengers and goods. The engineers were Thomas Grainger and John Miller from Edinburgh.
- The Wishaw and Coltness Railway.
-  Length: 11 miles (17.7 km). Incorporated on 21 June 1829 and partially opened on 21 March 1834. The engineers were Thomas Grainger and John Miller from Edinburgh.
- The Slamannan Railway.
-  Length: 12.5 miles (20.1 km). Incorporated on 3 July 1835 and opened on 31 August 1840.
- The Paisley and Renfrew Railway.
-  Length: 3 miles (4.8 km). Authorised on 21 July 1835 and opened on 3 April 1837 for both passengers and goods. The engineer was Thomas Grainger. Converted to Standard Gauge 1866.
Other early 19th century Scottish gauges
4 ft 6½ in gauge
In addition to the above lines, there were three railways, authorised between 1822 and 1835, that were built in the Dundee area, to a gauge of 4 ft 6 1⁄2 in (1,384 mm). They were:
5 ft 6 in gauge
Grainger and Miller built another two railway lines in the same area to a gauge of 5 ft 6 in (1,676 mm), (Indian gauge). Thomas Grainger is said to have chosen this gauge, since he regarded standard gauge as being too narrow and Isambard Kingdom Brunel's 7 ft 1⁄4 in (2,140 mm) broad gauge as being too wide. They were:
- The Dundee and Arbroath Railway;
-  Length: 14.5 miles (23 km). Incorporated on 19 May 1836 and opened in part in October 1838.
- The Arbroath and Forfar Railway.
-  Length: 15 miles (24 km). Incorporated on 19 May 1836 and opened in part on 24 November 1838.
End of Scotch gauge
The Glasgow, Paisley, Kilmarnock and Ayr Railway and the Glasgow, Paisley and Greenock Railway, which both obtained Parliamentary Approval on 15 July 1837 and were later to become part of the Glasgow and South Western Railway and the Caledonian Railway, respectively, were built to standard gauge from the start.
Use in Japan
After the end of Scotch gauge in Britain, the gauge revived in Japan. Since 1903, most of tram network in Tokyo was built with 4 ft 6 in (1,372 mm) rail gauge, called "coach gauge" (馬車軌間 Basha Kikan?). The use of this gauge extended to other suburban lines that projected through services to the city tram. Although Tokyo has abolished its major tram network, as of 2009, the following lines still use this gauge:
- The Keiō Line and its branches (excluding the Inokashira Line).
-  Length: 72.0 km (44.7 mi). Commuter railways connecting Tokyo and its suburb operated by Keio Corporation.
- The Toei Shinjuku Line.
-  Length: 23.5 km (14.6 mi). One of rapid transit lines in Tokyo built to provide through service with the Keiō Line.
- The Toden Arakawa Line.
-  Length: 12.2 km (7.6 mi). Only surviving line of Tokyo municipal tram.
- The Tōkyū Setagaya Line.
-  Length: 5.0 km (3.1 mi). Another tram line in Tokyo operated by Tokyu Corporation.
- The Hakodate City Tram.
-  Length: 10.9 km (6.8 mi). Only user of the gauge out of Greater Tokyo Area.
- Former operators.
-  The Keisei Electric Railway converted to 1,435 mm (4 ft 8 1⁄2 in) standard gauge in 1959.
- Whishall (2nd Edition)
- Awdry (1990)
- Robertson (1983)
- Tetsudō Yōran
- Awdry, Christopher (1990). Encyclopaedia of British Railway Companies. London: Guild Publishing.
- Robertson, C.J.A. (1983). The Origins of the Scottish Railway System: 1722-1844. Edinburgh: John Donald Publishers. ISBN 0-85976-088-X.
- Thomas, John (1971). A Regional History of the Railways of Great Britain. Volume 6 Scotland: The Lowlands and the Borders. Newton Abbott: David & Charles. ISBN 0-7153-5408-6.
- Popplewell, Lawrence (1989). A Gazetteer of the Railway Contractors and Engineers of Scotland 1831 - 1870. (Vol. 1: 1831 - 1870 and Vol. 2: 1871 - 1914). Bournemouth: Melledgen Press. ISBN 0-906637-14-7.
- Whishaw, Francis (1842). The Railways of Great Britain and Ireland practically described and illustrated. Second Edition. London: John Weale. Reprinted and republished 1969, Newton Abbott: David & Charles. ISBN 0-7153-4786-1.
- Tetsudō Kyoku, Ministry of Land, Infrastructure, Transport and Tourism (2008). Tetsudō Yōran (Heisei 20 Nendo) (in Japanese). Tokyo: Denkisha Kenkyūkai. ISBN 978-4-88548-112-3.