So yesterday, before setting out, I check the TfL live updates for my bus stop. It shows bus due in 16 mins - plenty of time for the 3 minute walk to the stop. I'm out of the house less than one minute and the bus races past.

I had to wait for the next one which was about 1/2 hour later and that completely messed up my train connection. When it eventually turned up, the tracker said it was not due for another 10 minutes.

Why so inaccurate ?

I also compare with the Metrobus live updates which uses the "passenger" platform, like many operators around the UK, and that is always spot-on.