Thank-you. Your post provides a good succinct summary of present-day issues around gauging. The arrival of high square-topped containers has added a new factor into the mix of considerations, but some of the other factors have been lurking for a long time. Back in the mid-19th century, early railway platforms in Britain seem to have been about 18-21 inches above rail level, roughly aligning with the lower foot-boards seen on Victorian-era railway carriages. It must have been very difficult for many passengers to clamber up from those low platforms into their compartments. Unsurprisingly, railway companies came under pressure to raise platforms, which duly crept up in subsequent decades until they reached a height of around 2ft 9in to 3ft above rail level, which remained the standard for most of the 20th century. In recent years, accessibility requirements have seen platforms resume their upward drift. The platform raising during the latter 19th century occurred during a period when the majority of Britain's railways were dominated by locomotives with inside cylinders. It does appear that the platform raising on some lines encroached into spaces where later loco designers wanted to place large outside cylinders. ES Cox wrote that, when the LMS was planning new outside-cylinder classes, there were particular problems with platform clearances at some locations on the LNW and Midland sections. Platform top-edge clearances on the GWR seem to have been a little less restrictive than on some other lines, and Churchward was able to make the design choice for his outside-cylinder classes to have their cylinders horizontal, low-slung and widely-spaced. On the 4-cylinder classes, the cylinder spacing had to be wide enough to allow for sideways movement from the adjacent bogie wheels. The result is that, not only are the GWR outside cylinder classes wider over cylinders than the majority of comparable engines from the other railways in Britain, but the point of maximum width tends to be at a lower height and more likely to come close to station platform edges.