Green Man Authority

Backstop:

Can't say I'm that enthused by the idea. In quiet spots it's not needed, it's already quiet. In busy spots there will be enough cars to make it an issue of time allocation, as it already is.

I think I've missed the point somewhere...

inappropriate_bike:

In quiet spots its hardly needed anyway because there will be sufficient gaps in traffic to cross.

In busy spots the lights will constantly sense vehicles approaching so will remain red for pedestrians just as much as they do now. Any other setup on a busy road would never be allowed, because the traffic capacity would be severely compromised

What am I missing?

Well, a number of things. Firstly, it's a lot harder to detect pedestrians than vehicles, which are generally in the carriageway. Pedestrians appear 'suddenly', from shop doorways, from subways, etc., they walk along the street on the footway in parallel to the carriageway and then want to cross the carriageway at a pedestrian crossing. The latter means that they take a 'sudden' small turn of about 90 degrees towards the carriageway. It will give them a big advantage if at that time the light is already green and they don't have to check themselves and wait, a big increase in walking comfort. Also, as for 'there will be sufficient gaps in traffic to cross'--sure, that's possible in London and most people do it. But think of parents with small children or nervous adults, e.g. people with mobility difficulties or elderly people, who might take a long time to cross the carriageway and who prefer to cross at a formal pedestrian crossing with a green man. Also, a small number of tourists might come from jurisdictions where crossing on red is unlawful, e.g. Germany, and who would otherwise wait until the lights turn green.

Secondly, remember that the main issue with through motor traffic in London is in the morning peak hour and to a lesser extent in the more spread-out evening peak hours. Basically, most of the nervousness about design and carriageway space and signal timings is mainly because of peak hour traffic volumes. At other times of the day, even 'busy' streets will have large gaps between vehicles and some that take high peak flows will even be fairly quiet. It's not as if 'quiet' and 'busy' streets are contraries, and there's plenty of scope for these measures to make a big difference even on main streets. (Clearly, there are streets like the A501 Inner Ring Road that are far more busy with motor traffic than they are ever quiet, and I don't expect that these measures will be introduced there, but most middle-ranking A-streets certainly qualify.)

Thirdly, a very important aspect of the success of such traffic signals will undoubtedly be whether they cut off large pedestrian flows too soon (i.e., as a vehicle approaches) or whether there will be some way of allowing for large numbers of walkers (e.g., people emerging from an Underground station) to be detected and for the signals to change only when the pedestrian flow has slowed to a trickle or all have crossed. That seems to me the most technically difficult aspect. I imagine that TfL probably envisage that this problem will be managed by either/both intergreen time or/and 'pedestrian countdown' (although the latter would make signal operation much less flexible in the event of a vehicle being detected). I'm not sure how that would work.

Fourthly, London's essentially a walking and public transport city, and the vast majority of Londoners get around in this way (and as walking is our default mode of transport, we all benefit, even if cycling, e.g. when you're looking for a parking space and only spot too late that the only available one is on the other side of the street), so that this will undoubtedly be beneficial to a vast number of people.

Finally, at the moment this attention-grabbing measure is actually only envisaged in ten locations. The vast majority of TfL's work is taken up with SCOOT, which isn't new but fairly old hat by now. Pedestrian SCOOT was trialled in 2014:

https://tfl.gov.uk/info-for/media/press-releases/2014/march/tfl-to-launch-worldleading-trials-of-intelligent-pedestrian-technology-to-make-crossing-the-road-easier-and-safer

@skydancer, cyclist SCOOT began to be trialled a year later:

https://tfl.gov.uk/info-for/media/press-releases/2015/june/new-pioneering-trials-to-detect-cyclists-at-junctions-begin-in-london

I don't know how far this has been rolled out by now, but I expect that there are still plenty of SCOOT systems in London that don't detect cyclists.

Now, I think that SCOOT is a mixed bag. It's obviously appreciated by many people if delays are reduced in this way, but I believe it can also serve to, over time, increase the flows it detects. I don't have evidence for that, but generally where better provision is made for flows that are already high, these flows will increase in volume, as per predict-and-provide; here, 'detect-and provide'. The biggest problem in transport policy is to do with unevenness of flows (i.e., providing for very high flows and dealing with the consequences of where flows are extremely small and don't sustain economic activity while the places with high footfall and wheel-roll benefit disproportionately), and I think SCOOT is very likely to exacerbate it, even where pedestrian flows are concerned. But, as I say, I have no evidence, it's just a logical consequence. Clearly, economic well-being depends to some extent on concentration of activity, but we have long passed the point where this is sustainable or otherwise advisable.