Indian gauge
5 ft 6 in/1,676 mm gauge is a broad track gauge commonly used in India, Pakistan, Sri Lanka, Argentina and Chile, but is also used on BART (Bay Area Rapid Transit), in the San Francisco Bay Area, United States. It is historically known as "Broad gauge" on the Indian subcontinent or "Provincial gauge", "Portland gauge" or "Texas gauge" in North America. It is the widest gauge in regular use anywhere in the world.
This gauge was first used in Scotland for two short, isolated lines, the Dundee and Arbroath Railway (1836-1847) and the Arbroath and Forfar Railway (1838- ).
In India, the Governor-General James Andrew Broun-Ramsay, 10th Earl of Dalhousie determined that a wider gauge than 1,435 mm (4 ft 8 1⁄2 in) standard gauge was more suitable for larger firebox and stability in high winds and long steep gradients.
"The first agreement of the Government of India with East Indian Railway Company and Great Indian Peninsula Company in 1849 stipulated that railways in India would be built on a four feet, eight and half inches gauge. However, soon there were disagreements with Lord Dalhousie favoring a 6 ft (1,829 mm) gauge and Mr. Simms, the consulting engineer favoring five feet and six inches gauge. The debate was finally settled in favor of the five and half feet gauge, called the broad gauge in 1850s and the first train that ran from Bombay to Thane ran on broad gauge."
...
Wikipedia