Re: @Stu Mac
The primary cause of motorcycle accidents where it isn't the fault of the rider is being shunted from behind at stops and traffic lights. If you filter between stationary traffic then this obviously can't happen to you, hence the reason we do it.
The same can be said for cyclists. Their cross-section from behind is considerably smaller than most motorbikes so they've got no chance if someone isn't paying full attention. At least bikers have their armour.
I'd be lying if I said it's not also nice to get ahead of the traffic though.