> In some places you'll get fancy live information screens which happily announce the arrival of a bus that doesn't exist

I worked on one of the systems for that many years ago, and one of the reasons TFL works better than many of the others is that TFL has (or at least had) extremely strict rules on what we were allowed to show.

E.g. if the display could not contact our servers, we were required to remove the buses after about a minute to prevent showing stale data (same freshness criteria applied to what our servers were allowed to forward to the frontend. We also needed to prove we handled clock drift correctly for the same reason. They put us through extensive testing to ensure no stale data before any displays went live.

If you see buses in London disappear from a display, those criteria will often be the reason - TFL considered it better that a bus was missing than that people would be incorrectly told it was close.

> If you see buses in London disappear from a display

Thanks for that explanation! Was an alternative considered—e.g. marking the bus as "lost" instead of removing it altogether? Discounted because of space constraints?