There is no mention of an experienced bridge designer.
Renzo Piano is an Architect who has no apparent history of bridge design. Salini Impregilo are contractors; and Fincantieri are boat builders with again no record of bridge construction.
HS2 seems to be badly planned throughout, with inadequate connectivity where it is needed.
A real re-design is needed, not tinkering at the edges. The HSUK proposal seems to be better thought out, at least in connectivity terms.
It has the advantage also of not going through the Chiltern countryside.
Comment on: HS2 claims third of government rail budget
I do not think HS2 as currently designed would pass any realistic cost benefit analysis. On this basis alone it should be drastically re-planned, as a practical solution to a capacity problem, instead of a "we must have a fast train" vanity project. The other real problem is the lack of connection with HS1. I know that Euston to St Pancras is not far, but for travelers with large suitcases, even the short underground journey would be difficult.
Don't kill the idea of a new route to the North & Scotland, but it must be more re-thought.
Youtube also has another video of apparently the same collapse, taken from further away, but also showing the same collapse, and shots of the collapsed structure.
For two separate people to be recording the same bridge at the same time implies that they strong reason to believe something would happen, if not the collapse.
This is worrying for many reasons, which I am sure I don't need to list.
Could there be an election coming in 2020?