I don't think I can support the Golden Gate Bridge Proposal, for although it is iconic, its technical advances were limited to it being bigger than the proceeding largest Suspension Bridge.
This is where I am in a sticky situation as many of the great breakthrough engineering feats of the industrial revolution mostly occurred in Britain, and we can't propose sites from our own country (by the way this was the only one from the UK I thought would be worthy of a Top 50 space).
I have long thought of attempting to get a cohesive tie around projects spread throughout the country into some sort of 'Infrastructure of the Industrial Revolution in the Britain' style proposal.
This would include projects such as; the Menai Straights Birdges including the world's first suspension bridge (and perhaps their miniatures in Conwy), Pont-Cysyllte Aqueduct, Clifton Suspension Bridge, Selected parts of the Great Western Railway (Box Tunnel, Maidenhead Railway Bridge, Paddington Station etc), Leeds-Liverpool Canal, Stockton-Darlington Railway, Forth Rail Bridge, Selected parts of London's subterranean infrastructure e.g. Thames Tunnel and parts of the Metropolitan Railway line, perhaps the already inscribed Ironbridge of Ironbridge Gorge and early steam railway in Cornwall, maybe more.
Now I think it is very disparate and unfocussed, but I am thinking that serial sites such as the Belfires of Belgium and France and Pilgrimage Routs to Santiago are developed over a long period of time and contain different facets, maybe for coherence it could be reduced to the works associated with just Brunel? But with some work it would be something that would meet the four criteria set out by Solivagant and to some extent I think it could claim to be the maximum that each criteria could achieve.
a- These were the first of nearly everything, first 'railway', first suspension bridges, first Iron bridge, first underwater tunnel, first underground railway.
b- The influence of these projects essentially redefined the building of infrastructure throughout the world not just limited to the region or British Empire.
c- These were the means by which the industrial revolution redefined production and society, which has had an effect on almost every corner of the world. They enabled Britain to become the predominant world power of the age.
d- These contain several iconic projects most notably the Forth Rail Bridge but also Clifton Suspension Bridge, Menai Straight's Bridge, the 'Tube'
I think this would make it worthy of a place in the Top 50 missing in my opinion. But of course I am not proposing it as I am excluded from proposing a site in my home country.
In addition I support the Panama Canal proposal, for both the technical achievement and also as a display of the economic and political emergence of the USA.