[[File:Checking the gauge at Plymouth.JPG|thumb|Track maintenance workers checking the gauge at {{stnlnk|Plymouth}}, England]]
Infrastructure owners specify permitted variances from the nominal gauge, and the required interventions when non-compliant gauge is detected. For example, the [[Federal Railroad Administration]] in the USAUS specifies that the actual gauge of a 1,435 mm track that is rated for a maximum of {{convert|60|mph|km/h|1|abbr=on}} must be between {{Convert|4 ft 8|in|mm|sigfig=4|abbr=on}} and {{convert|4 ft 9.5|in|mm|abbr=on}}.<ref>{{cite web|url=http://www.fra.dot.gov/downloads/safety/tss_compliance_manual_chapter_5_final_040107.pdf|title=Track Safety Standards Compliance Manual Chapter 5 Track Safety Standards Classes 1 through 5|publisher=Federal Railroad Administration|access-date=26 February 2010|url-status=dead|archive-url=https://web.archive.org/web/20080528020612/http://www.fra.dot.gov/downloads/safety/tss_compliance_manual_chapter_5_final_040107.pdf|archive-date=28 May 2008}}</ref>
==Advantages and disadvantages of different track gauges==
