I often have the experience of a bus starting to overtake me a reasonable distance away, then pulling in too early so that the rear of the bus nearly hits me. It is also common to have the experience of a bus overtaking a cyclist and immediately pulling in to a bus stop, cutting across the cyclist’s path.
I have wondered why this happens so often; surely they can’t all be doing it deliberately! The only other explanation I can come up with is that they think “bicycle = slow, so I can treat it like a stationary object”.
The picture on the left shows a diagram of a bus overtaking a stationary cyclist. It takes about three bus lengths. However, if the cyclist is moving at half the speed of the bus, it will take at least six bus lengths as indicated in the image to the right. This is a fairly typical scenario, for example with the bus travelling at 30mph and the cyclist at 15mph.
I suspect many bus drivers aren’t really aware of this.
An implication that leads on from this is that, if there is a bus approaching from behind a cyclist who is approaching a pinch point (narrowing of the road), the cyclist ought to be taking primary position (“claiming the lane”) when they are at least six bus lengths from the pinch point. For a normal British double-decker bus, that is 90 metres away.