Two UK Railway What Ifs

Got a couple of questions regarding changes to the history of the British railways. Technically this could go in the Before 1900 forum since that's when the points of divergence are but I'm mostly interested in possible modern consequences.

I was reading a book a few weeks ago, I forget the title, but it mentioned that during the planning stages of the London & Manchester Railway there was a debate between the Rennie brothers, John and George, and George Stephenson over what track gauge to use. The Rennies favoured 5ft 6in, what was later became known as 'Indian gauge', whilst Stephenson preferred 4ft 8.5in, what became the 'standard gauge', with the author arguing that since there was only roughly 375 miles of railway track in the UK at the time with much of it being disjointed small lines and the L&MR being the first trunk line that if they had gone for 5ft 6in if would have established it as the effective default standard. Now personally I'm somewhat rather sceptical of this claim, much as I was of a number of other claims they made, but suppose for a moment that 5ft 6in had been used and become the default standard, would it have created any major differences over time? As I understand things the wider the track gauge the larger the minimum curve radii needed but other than that I have no idea.

For the second scenario back in the early days of the railway industry if you wanted to build a railway you generally needed an act of parliament to help with things such as setting up the company as a limited liability one and with buying the land needed for the tracks. Enter Robert Smith, Member of Parliament for Dunny-on-the-Wold, who is both popular and influential in the House. Whilst generally supportive of these new-fangled railways he's also something of a claustrophobe so when the various acts start appearing over the years he uses his position and influence to have a minimum tunnel size and distance from the trains rule added to each of them, coincidentally this just happens to work out as roughly what the modern day European loading gauge happens to be. As is the British way of things since over the decades the rule keeps getting added after a while it effectively becomes convention, eventually becoming the official standard. Aside from the obvious knock-on effects such as raising costs somewhat due to slightly taller or wider tunnels and bridges having to be built what are the likely knock-on effects?
 
For the second scenario back in the early days of the railway industry if you wanted to build a railway you generally needed an act of parliament to help with things such as setting up the company as a limited liability one and with buying the land needed for the tracks. Enter Robert Smith, Member of Parliament for Dunny-on-the-Wold, who is both popular and influential in the House. Whilst generally supportive of these new-fangled railways he's also something of a claustrophobe so when the various acts start appearing over the years he uses his position and influence to have a minimum tunnel size and distance from the trains rule added to each of them, coincidentally this just happens to work out as roughly what the modern day European loading gauge happens to be. As is the British way of things since over the decades the rule keeps getting added after a while it effectively becomes convention, eventually becoming the official standard. Aside from the obvious knock-on effects such as raising costs somewhat due to slightly taller or wider tunnels and bridges having to be built what are the likely knock-on effects?
Are we talking railway gauges here, as in structure gauges rather than track gauge ... as in W6, W7, W8 etc.?
 
The bigger space between the frames of most locomotives might mean that compounding gets a fair trial, though I imagine most British locomotives would be squatter to reduce the risk of of toppling on sharp curves. Everything is going to need to be bigger, wider tunnel bores, in fact cutting would be the norm, unless it was unavoidable. Basically, larger everything, and therefore probably less cash so fewer branch lines.

Have a look at Ireland and try to appropriate it.

Luath
 
Why only go to 5' 6"? Under Isambard Brunel, the Great Western built tracks to 7' gauge. It was called the War of Gauges, and my understanding is that railfans have thought a lot about what would have happened if the much broader Brunel gauge had prevailed.

Personally I think the differences would be relatively small. The main tradeoff in gauges is that broader gauge is more expensive and has a higher minimum curve radius but is more stable and allows higher speed. As a result of the benefits of broader gauge, no high-speed rail line in the world uses narrow gauge, even in Japan and Taiwan, which are island countries with a narrow-gauge legacy network. (Spain has a broad-gauge legacy network but uses standard-gauge for high-speed rail for compatibility with France; Russia uses broad gauge for both legacy and high-speed rail.)

So, let's imagine a world in which mainline railroads used Brunel's gauge. Britain would have wider space between tracks, so it would be able to run wider trains, about as wide as Scandinavia and Russia run today (there's a 2' width difference). The (standard-gauge) Liverpool and Manchester had standard-gauge spacing between the two tracks, to allow oversize trains to run in the middle, and even with subsequent widening of the track spacing, it limits Britain to narrow trains. In contrast, doing the same spacing with the Brunel gauge would result in track spacing that's about on a par with that of Japanese bullet trains and not much narrower than European ones. The result is that trains in London and to some extent Paris would be considerably less crowded. Outside Britain and sub-Scandinavian Continental Europe, the difference would be quite small, since the tracks already have a fair amount of space between them.

Moreover, broad gauge is stabler, making it easier to run double-stacked container freight. Indian gauge, which is broad but still much closer to standard than to Brunel, is already sufficient to run double-stacked containers on ordinary flatcars; standard gauge is not, so the US and China run double-stacked containers on well cars, with lower centers of gravity. So logistics in the US and China would be a bit cheaper; Europe has pretty much zero double-stacked container freight because of low clearance, and wider gauges would not have changed that. Tunnel bores would be wider and thus taller, as Luath notes, but bridge clearances would be approximately the same.

Conversely, mountain railroads would be more expensive to build, so there would be fewer of them. Even standard gauge is too much for some, so a lot of mountain railroads are narrow-gauge: the Denver and Rio Grande had an extensive network in the Rockies, which was either abandoned or converted to standard; Switzerland has a fair number of narrow-gauge lines; and Japan is narrow-gauge because of all the mountains. Conversely, the higher track construction standards on the railroads that would be built would allow much higher speeds, because of the wider curves, so trains wouldn't crawl as much. It still wouldn't be high-speed rail unless it were built as such, but I'm guessing that all major mainlines would be able to maintain 100-120 km/h average speed, even through mountains; the current average speed between Zurich and Milan is about 70, which compares unfavorably with Amtrak, let alone non-mountainous European mainlines.
 

Saphroneth

Banned
Bizarrely, one of the knock ons might be a long way in the future - better British tanks!
(Famously they had to fit the loading gauge of UK trains...)
 
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