About gauges ...

In Victorian times there were two common gauges for the mainline railways of Britain. Most companies adopted what we, in Britain, now refer to as ‘standard gauge’: that is 4ft 8½in between the rail-faces, as above.

My engineering hero, Isambard Kingdom Brunel, here immortalised in bronze, was a man of big ideas.

For his Great Western Railway he insisted upon 7ft 0¼in:

Smaller industrial and rural enterprises, unconnected with main lines, used several different narrower gauges, partly because such gauges permitted tighter curves. On the Isle of Man Railway you'll find 3-foot gauge, and on Welsh mountain railways - 2'3".

Irish Railways, for some contrary reason, (keep the Brits out?) finally ended up with 5ft 3in for their main railway lines.

Brunel’s argument for adopting the broad gauge on the GWR was that it would facilitate higher speeds, improved comfort and greater load-carrying capacity. Wider wheel-based locomotives could accommodate boilers placed lower than their standard gauge counterparts. Thereby a lower centre of gravity would lead to greater stability. Cylinders could be situated between the mainframes, (inside cylinders.) Again, this might have contributed to stability, but one wonders whether reduced accessibility could have created difficulties with maintenance.
That debate: "What if … ?" continues to this day.

Some of Sir Daniel Gooch’s designs for the GWR must have been fire-breathing monsters of their time.
Here's Iron Duke:

Interestingly the permanent way for Brunel’s broad gauge railway consisted of rails supported on longitudinal sleepers, in contrast to the still-familiar transverse sleepers of the standard gauge:

Perhaps the biggest problem that signalled the demise of broad gauge was the time, labour and inconvenience involved in transhipment of passengers and freight between the rolling stock of rivalling companies:

After 1864, when the British parliament accepted advice from ‘the gauge commission’ that 4ft 8½in should be adopted nationally, there was some dalliance with mixed gauge, but 1892 saw the final demise of Brunel’s broad gauge as the last broad gauge train left Swindon:

Notice the longitudinally-sleepered broad gauge track on the right, mixed gauge with intricate point-work/crossings in the centre, and standard gauge to the left.

Isn't all that terribly interesting?

My next project will be about bridges.

The terms 'cantilever', 'suspension', 'box-girder' and 'truss' come to mind!