BentMikey said:
Except that you made the point that the slower cyclists cause tailbacks of motorvehicles at junctions, unless I've misunderstood. My point is that these same slower cyclists are acting to reduce queueing time and length.
Slower cyclists in primary tend to cause tailbacks
to junctions, with the knock on effect that fewer vehicles get through leading to more or less static traffic.
So, for example, if I turn left from Milton Road on to Arbury Road, I've got a short distance before parked cars in front of me, and I've usually got traffic on the other side of the road. An assertive cyclist (like me) will take a strong primary and prevent overtaking there, because it ain't safe. I might be going at 17mph (on average, from a standing start and not hurrying).
Most slower cyclists will be right in the gutter around the corner, then they're desperately looking for a way out into the traffic to get past the parked cars. If instead the slower cyclist does the right thing, gets into primary because it just ain't safe to allow overtaking there, then a good five or six vehicles that might have passed haven't, and the whole stream of traffic is stuck behind him at 11mph. Knowing that junction well, I know that when this happens something like half of the number of cars that normally get through at red can do so. Because thats a left filter lane that means that when its busy the lane then fills up and traffic backs right up to the roundabout way further back.
In some traffic situations slower cyclists mediate traffic speed and keep things nice and even. In others, assertive slow cyclists (most especially when there are plenty of them) grind traffic to a stop. I don't blame them for it, it isn't their fault that there are loads of cars clogging up the roads and they certainly shouldn't ride dangerously to free up the traffic. But my observation is that the effect can be rather frustrating for the motorists, and rather clogging on the road.
A few such cyclists do nothing bad for traffic flow. When you see lots of slow assertive riders things seem to change, except of course in exceptionally heavy traffic (which in some parts of London and some other city centres is the norm).