Contrast with the UK where 'filtering' is legal [0] and I have never heard anything negative about it. Riders filtering won't cause me as a driver any delay.

[0] Rule 88: https://www.gov.uk/guidance/the-highway-code/rules-for-motor...

I've always found the American 'no-filtering' rule incredibly strange. Whenever I'm stuck in traffic in the UK (in a car), it's a completely normal sight to see bikers and cyclists filtering to the front of the line.

I've seen large motorbikes fitting through gaps that simply don't look big enough, but I've never actually seen anyone get a wing mirror knocked off. (I guess bikers develop a very accurate mental picture of how wide their bike is).

Nobody considers it rude, as it doesn't slow down the cars in the slightest. The bikes simply fit through the gaps. Can anyone explain the American take on this?

Legal and encouraged in CA.