So i've been researching the way in which the road/rail infrastructure of scotland was built in the c18th/19th, obviouly it is particularly constrained by large mountains and very wide lochs.
This lead me to stumble upon a bridge type never used in the UK but used in several locations in America. in the nineteenth century. As an engineering solution, there is no reason it couldn't have been used, it just wasn't.
The Pontoon Railway Bridge:There were apparently a small number, over wide waterways which precluded intermediate piers, including at Wabasha Missippi, Marquette Iowa, Chamberlain South Dakota, according to the article
here (which has photos) [Book: North American Railroad bridges, pp140-1] The longest lived and best documented seems to be:
1874-1961 Prarie du Chien Pontoon Railroad Bridge ( Chicago, Milwaukee & St Pauls Railroad)
Replaced railroad ferry over the Missippi. Closed 1961. Able to deal with large variation in water level too.
Drawings etc in a 1932 article
here &
here.
It seems that, predictably,the bridges have low maximum loads, and low maximum speeds. And those with opening spans were very expensive to operate because of the manpower it required.
I'm not saying it was a common bridge type, but neither were cantilever bridges or some of the tall metal bridges (Crumlin, Meldon etc). It appears seattle is currently planning to run its light rail system accroas the I90 floating bridge (in due course).
For interest, I did also find
this image but I'm not sure how permanent that one was...
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Given the (realistic) in game prohibition of building most bridges over deep water (due to intermediate piers), this is precisely where such a bridge was used. as an alternative to a "forth bridge" style construction. (Forth bridge opened 1890)
I suggest it worth adding to pak-britain because it fills a niche no other bridge type can fill. We often play using maps different than the real UK geography so it may be useful. On a water-heavy map it would be invaluable.
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I'm now off to ponder how to network scotland via floating bridges...