He finds out at first hand what Ballasted Track Renewal is. According to Boris it's "absolutely crucial for the improvement of services on the District Line and all sub-service lines". The video is another example of TfL efforts of trying to show engineering work in action (Tube chief Peter Hendy stressed this was something he wanted to do when I met him with other London bloggers last year).
In the video Boris says of the track replacement: "Once it's done this track won't need renewing for another forty years". Not sure how much I'll be using the Tube when I'm a pensioner, but let's hope it's true and will save future commuters the frequent line weekend closures we've been facing.