Do you know how reliable is the realtime info? I find that Google maps very often says “bus coming in 4 min” as im watching the bus drive away. Or “delayed by 5 min” and it’s early by 2, etc.
IME Google's realtime data in many places isn't very good; even where it _claims_ to have realtime data (there's a little radio symbol beside the bus), it sometimes disagrees with both the local operator's own realtime data, and, well, consensus reality.
> Or “delayed by 5 min” and it’s early by 2, etc.
This, in particular, you can never really trust, especially for buses, no matter who's telling you it. If a bus is delayed 5 minutes, and has the opportunity to make up the time, it will. If a bus is delayed by five minutes, but there's no-one at the next five stops and no-one wants to get off there, it may well be on time by the time it gets to the next stop. In many bus systems, buses will sometimes just stop to avoid getting too far _ahead_ of schedule, though.
In my experience in NYC, the subway data is extremely accurate in terms of the minimum time until the next train. The subway virtually never arrives "early".
Buses seem to have a problem where their location transmission sometimes fails for a few minutes. The system always assumes the bus is still stuck at its last reported location rather than moving. That's why you get a bus arriving when the feed says it's 4 minutes away.
A good rule of thumb is that if you see the minutes away change, e.g. from 7 to 6 minutes, it's accurate. If it's not changing (e.g. just sits at 7), it might be because it's genuinely stuck in traffic, or because it's stopped transmitting. (Which explains the "delayed by" situation you describe.)
