Link 1: Crossrail TBMs
Link 2: Near You - Crossrail - Crossrail [Current locations and progress of TBMs]
Wonder which over paid bod a city hall has the job of updating those twitter feeds rather than getting something productive done...
They have all the location information already. Not very long to copy it into a tweet and score some social media brownie points.
EDIT - Actually, description says it's a bot and it isn't official. Looks like someone's coding project to scrape the data from a public server and announce it on Twitter.
That's look interesting compared to this: https://twitter.com/big_ben_clock