Moreover, if you're a bicyclist and there's no bike lane (or insufficient bike lane) so you'll have to bike erratically if you don't take the lane then take the lane. Signal, make sure it's clear, and do it early. The safest thing everyone can be is predictable.

I feel the problem is that we're deeply over-trained to read cues for what a car will do, and less so for bikes. To whit, if a bike _could_ dart in front of me, I assume it will. Much like a squirrel, deer, or inner city car in a traffic jam.

Edit: actually, I would probably hit the squirrel. Swerving/sudden speed changes are often far more dangerous. Hopefully the point holds: if you always feel the need to fail safe, then expect congestion and traffic problems.