Traffic on the main carriageway heading south continued to flow for quite a while after the cycle lane had gone red. If I'd stayed on the road I'd have been a couple of minutes ahead.
I've just checked out how long I was held up (via Strava fly by) and at each set of lights I had to wait approximately 1m25 (so nearly three minutes in total over a short stretch of road). That's not very convenient, it feels like being a freight train stuck in the goods loop for the fast motorised traffic to pass, not like being on a superhighway. Maybe I was just unlucky. I've never seen the light at the crossover on green, maybe it's controlled by a sensor so not triggered unless you enter the lane (so in that respect not much better than the push-a-button-and-wait crap you get at a toucan).