Originally Posted by JeffS
Why do we say a car passes a bicycle and a bicycle filters past a car?
According to the vehicle code in most places,
passing is expected to be done on the left, consistent with the rule about slower traffic staying to the right (like bikes, usually). Passing on the right is usually prohibited, which is why it is probably illegal even for bikes, unless another law explicitly make it okay for bikes, which is the case in some places. Anyway, that's probably why we say "filtering" when we mean "passing on the right". I would call a bike passing on the left just "passing", and is more consistent with the spirit of the law, if not the letter as well. In some places, the bikes-to-the-right rule contains an exception for passing slower moving traffic, to make it clear that bikes are allowed to pass on the left just as cars are supposed to.