Is there any good reason a cyclist would do this?

[RobinsAreTerritorialFuckers]

Coming up to a roundabout, there are two lanes, plus a cycle box at the front. There is also, for what it's worth, a subway under the roundabout which is bike-accessible, for people who choose to use that. Traffic lights at the junction, so plenty of time to get into the cycle box, which was empty.

I was in the left-hand lane, signalling left. In front of me there was one car, but with plenty of space to its left. Three cyclists were to the left of us, in a row so that the first one was ahead of me (beside the front car) and the last was level with me. When the light turned red I saw her stick her arm out, wave to the others, then wobble and grab her bike again. So I figured she wasn't steady. In retrospect it is possible she thought this was a signal.

When the lights turned green, the cyclist in front started to cycle out in front of the front car and to the right (the car was a bit slow off the mark). Car ziggles forward and cyclist stops. Then all three started trying to move right across in front of the cars. I'd started to move but stopped over the junction.

It was all slow so no chance of hitting anyone - though there was plenty of honking from people behind who couldn't see why we'd started then stopped - but is there any reason a cyclist would choose to turn right from the left-hand lane, rather than using the cycle box or cycling in the correct lane?

Sorry, I misunderstood you, I thought they had stayed in the left hand lane right around the roundabout, but had gone in front of the people trying to exit the roundabout at the next junction.

No, I'm fairly sure they wanted to get into the right-hand lane. The first one went out in front of the front car, and to the right, then all of them tried. When I stopped and everyone was honking, two of them stopped, and I'm not sure what they did after that because I made my turn.

I am talking about them moving right across the cars from the left hand lane.

That is exactly what they are taught to do in DC cycling proficiency class. But stand on left until no car is present (in theory wait for a clear time, stand on left until they are ready to execute maneuver). The problem is, these guys got it half wrong (didn't wait fully). Not taught to be confident about standing on the right side of the lane, maybe, or forgot to wait until all cars had passed... probably that never happens.

This is the opposite way to use road, of what I was taught in 1970s.

So - can I just check we're definitely talking about the same think ll - you mean they end up moving from the left-hand lane into the right-hand lane? And then, presumably, back to the left when they want to turn off?

Given it was 3 of them all doing the same thing, I'd say that they got pushed left by the traffic on the approach to the junction and found they couldn't safely or confidently move to the right to solidify their position, and then perhaps the cyclist in the front blocked access to the box to the back 2 (that's if all 3 weren't cycling in a party)?

I regularly have to ask other cyclists to move forward into the cycle box at junctions as I find the first arrivals stick left and nobody can get past. I've taken to just sitting in centrally in the lane in traffic at some junctions now to ensure I'm visible as there's so many bikes on my route.

(Only if I'm moving right, I basically just pretend I'm a car...)

I think from the way they were moving they were all together, but you may be right that the two further back were wrong-footed by the one in front - makes sense. Thanks.