My first optimistic view on this scheme appears misplaced. I wondered at the change of heart from TfL at installing cycle "early start" lights when they had been previously been adamant that any help for cyclists or pedestrians would incur an "unacceptable" delay to motor traffic. I now realise that there has been no change of heart - the cycle scheme at the roundabout is a massive compromise for cyclists in order to make sure there is absolutely no compromise in "traffic flow".
The videos put up by TfL
here illustrate the issues.
The scheme at the roundabouts is basically a deep ASL with a filter lane. The ASL is controlled by standard traffic lights applicable to all road users, whilst the filter lane has a cycle specific light before the cyclist enters the ASL.
I think this works (I use the word
losely) as follows.
1) When cyclists are in the ASL, they are held by the "standard" lights at red; whilst these lights are red, the cycling filter light is green to allow entry to the ASL.
2) The cycle filter light then goes to red to prevent any cyclist filtering from progressing to the ASL as the "standard" lights go to green.
3) The standard lights go green and the cyclists and vehicular traffic set off at the same time (Ok, so the video shows the front standard lights changing a fraction of a second before the ones at the back of the ASL, but I suspect most drivers will start to move based upon the lights in the front of the ASL anyway, and even if they don't the timing appears to be in the order of a second).
This means that
1) Cyclists will have to wait a minimum of 1 traffic light cycle (if they arrive at the filter when the standard lights are red) or a maximum of 2 traffic light cycles (if they arrive as the standard lights are turning green, but the filter light has turned red). Cyclists will therefore wait for around twice as long as vehicular traffic to negotiate the roundabout - assuming of course that cyclists don't just get pissed off and jump the filter or use the standard carriageway instead.
2) The cyclist "early start" is simply the time between the cyclists at the front of the ASL moving off and the time taken for the vehicular traffic to traverse the ASL. If you are slow at taking off and the cars behind are quick, it looks like there will still be conflict. And that is with the optimistic assumption that this ASL will be
unique in not generally being encroached upon by the vehicular traffic anyway - at which point all "early start" advantage, no matter how small, disappears. Considering that the junction generally tails back at peak times, I would assume the ASL will be full of queueing traffic that didn't make the change in lights in time.
I am really pissed off at this scheme, now I understand what TfL have done. This is basically a rubbish attempt to give cyclists some head start, which probably will be massively compromised by encroachment of vehicles into the ASL anyway, and an attempt to separate cyclists by holding them up for possibly twice as long as the average motor vehicle. And it won't work anyway since some motorists will simply ignore the ASL as per usual. The whole scheme is massively compromised by TfLs utter obsession with traffic flow, to the point it won't work.
Maybe the flyover scheme will be better than the roundabout one. But I am somewhat more than cynical that the "proposal" for the flyover will ever be more than a suggestion on paper. Since it would involve lights that
would have to affect traffic flow to aid cyclists onto the flyover, and removing a traffic lane to implement a cycle lane east-bound, I assume that the proposal will be quietly dropped as "impractical"
I expect that this scheme will mean most cyclists will continue to use the flyover as now, and that cyclists who don't want to negotiate the carriage-way to reach the flyover will have to use this scheme where they are delayed in order to be offered pretty much zero time advantage to pass the A12 exits before vehicular traffic comes, once again, into conflict with them.
I think that, by now, you may be able to guess where I believe TfL should shove this particular plan.