I went through there today; they've certainly been busy since I was last there about a month ago. What is the new steel structure being built over the Overground tracks North of where the Underground tracks cross them? It's not a bridge crossing the tracks, it looks more like an upper deck running on top of them, but it can't get any further South than it does now, because the bridges carrying the high-level tracks are in the way.

If that's what they've just done in a four day closure then they've done well. Can't be the easiest place to crane things into and out of.