Until this piece of legislation was passed, different local railways had used a range of gauges (width of distance between the two rails) for their tracks. For railways in steep mountainous areas, for example, a narrow gauge was useful for enabling a locomotive to follow a tighter curve, while Isombard Kingdom Brunel chose a wide gauge for his Great Western Railway from London to Bristol. According to the terms of the new Gauge of Railways Act, however, passenger railways in Britain could now be nothing other than 4 feet 8 and a half inches across.
Editors. "Britain adopts a standard railway gauge". The Literary Encyclopedia. First published 30 August 2013
[http://www.litencyc.com/php/stopics.php?rec=true&UID=4892, accessed 21 January 2017.]