This is also the case in the Seattle area. For example, Bothell-Lake City Way has a transit lane to facilitate the ease of travel for the buses. If the issue was only keeping auto traffic moving, they'd only need cut-outs for the bus to pull into at each stop.
Fbloogyudsr, however, may be refering to the bus lanes in downtown. Here, I think the focus is to indeed keep the other motor vehicle traffic flowing.
Whether or not bicycles were permitted in the transit lanes like Lake City Way was discussed on a local cycling commuter board, but I don't remember the conclusion. Certainly it is a common practice on the weekends, when the buses don't run as frequently and traffic is generally lighter. I think there was some concern about cycling in the bus lane at rush hour when car traffic is basically stopped and the bus in barrelling down the narrow diamond lane at 40 mph.
Downtown is another issue. If you are cycling on Second or Fourth, which are one-way and have the bus lanes, you want to be on the far left, not on the far right. (In Washington State it is legal for cyclists on one-way streets to be as close to the left as practicable as well as right.) The bus lane simply has too many vehicles pulling in and out to be safe for cyclists.
-- Warm Regards,
Claire Petersky See the books I've set free at: