Editing Loading gauge (section)

=====Tube lines=====
* [[City and South London Railway]] was built with tunnels of only {{convert|10.5|ft|m|2|abbr=on}} diameter. Enlarged for [[Northern line]] to {{convert|12.0|ft|m|2|abbr=on}}
* [[Central line (London Underground)|Central line]] with tunnels of {{convert|11|ft|8+1/4|in|m|2|abbr=on}}, increased on curves, reduced to {{convert|11|ft|6|in|m|2|abbr=on}} near to stations. This makes Central line trains unique on the [[London Underground]] system because, although the loading gauge of the rolling stock is the same as the other 'tube' lines, the smaller size of the tunnel requires that the positive [[Fourth rail|conductor]] rail is {{convert|1.6|in|abbr=on}} higher than on all other lines.

A Parliamentary committee headed by [[James Stansfeld]] then reported on 23 May 1892, "The evidence submitted to the Committee on the question of the diameter of the underground tubes containing the railways has been distinctly in favour of a minimum diameter of {{convert|11|ft|6|in|abbr=on}}". After that, all tube lines were at least that size.<ref>{{cite magazine |magazine=Railway Magazine |date=February 1959 |pages=94–96 |first1=Michael |last1=Robbins |title=The Size of the Tube }}</ref>

* [[Piccadilly line]] with tunnels of {{convert|12|ft|m|2|abbr=on}}
* [[Victoria line]] with tunnels of {{convert|12.5|ft|m|2|abbr=on}}; enlarged to reduce air friction.
* [[Glasgow Subway]] with tunnels of {{convert|11|ft|m|2|abbr=on}} and a unique track gauge of only {{Track gauge|4ft|lk=on}}.
* [[Tyne and Wear Metro]] with tunnels of {{convert|15.5|ft|m|2|abbr=on}}; built to mainline rail network standards.