Undertaking / filtering on left?

This is often dangerous as well. When traffic starts moving again, you're suddenly out in the road and moving more slowly than the vehicles, who are generally unaware of the need for you to get back in quickly. Undertaking has it's risks, but this is quite intimidating for any cyclist, especially newbies.

Yes, of course you need the skill to make the right judgement call each time. It's not that hard to anticipate what a queue will do, though. If you watch the traffic signals, which should be visible ahead, you can predict when you can slot yourself into the queue again. There really shouldn't be any 'suddenly' if you pay attention.