Well, looking at the Street View, the two lanes appear not to start until after your junction, but it's one of those situations where people try and skip the queue into town to turn right. When I used to travel towards Cannock every day, I often used to see one driver who would skip a considerable queue, make a complete circuit of the roundabout then rejoin the queue into town... I think they tend to paint 'keep clear' on the road, although I'm not entirely sure what regulation decides between a yellow box and a 'keep clear' - it would certainly seem like the right sort of junction to do this for, especially at peak times. I would have thought that either a yellow box or 'keep clear' would help, if the traffic is queuing. A lane specifically to turn right would help of course, but would probably irritate those wanting to head to Baswich when the A34 is queuing into town!