Forum topic: Will low-traffic neighbourhoods reduce net pollution?

It is often quoted that 36% of car journeys are short enough to be walked or cycled and it is claimed that LTN’s encourage this by not allowing traffic to drive through . The longer car journeys both in distance and time (extra time being due to both congestion and extra distance) make the decision to walk or cycle the better choice. Let’s examine this mathematically.
So in every hundred cars 36 fall into the category of a 3-5 minute drive that could alternatively be walked or cycled. Let’s assume a certain proportion could/would not disappear due to say disability, carrying heavy loads such as the weekly shop, particularly bad weather etc. If the scheme achieved a removal of 20 of these car journeys effectively reducing short car journeys down to just 16% I’m presuming this would be close to a best case scenario.
Looking at an original 100 car trips, you will have reduced this 100 to 80 car trips and saved 20 x 4 mins average, or 80 minutes of car time on the road. The other 80 cars that are still left on the road however will only have to be delayed for 1 minute on their journey to cancel this out. Those in support of LTN's claim “people should be prepared for an extra few minutes on their journey for the good it is doing”, well in this case a “few “ extra minutes will be considerably increasing pollution as well as condensing it over a smaller area with queueing traffic dispersing it less. This queuesmog is far more dangerous for walkers, cyclists and the residents who have to live with it constantly.
The argument may be with that with 20% less cars there will be less congestion! Well I guess in that case the people who were persuaded to forgo shorter car journeys because of the longer journey times will now get back in their cars again. Can you really reduce net pollution by trying to force cars off the road with longer journeys and congestion ?

You are assuming people will 'get back in their cars again' - many will ditch their cars for good (its already happening in our road) and many others will enjoy the new found benefits of walking and cycling and reduce their car journeys anyway. You are also assuming some very short journey times - the 35% figure refers to distances of under 2km - these can easily take longer than 3-5 mins. And of course some people will be persuaded to cycle longer distances or use public transport. The only way of reducing traffic is to have less vehicles and ltns help in that goal (we also need vehicle owners to pay the true cost of owning a vehicle). Over the past ten years drivers using unclassified roads to cut through the residential neighbourhoods and shorten their journey has risen dramatically. Once upon a time only ‘those in the know’ diverted from the surrounding ‘A’ roads, but use of Waze, Google Maps and other wayfinding apps means many more drivers now divert down unclassified roads to knock a few minutes off their journey time. Indeed since 2009 traffic on unclassified roads in London has increased by 72%, whilst on A roads it has fallen 1% (and of course the vast majority of people live on the former; very few on the latter).

For the speed I refer to Transport For Londons “ Roads Task Force thematic analysis” which you can find here http://content.tfl.gov.uk/technical-note-09-how-does-the-road-network-perform-in-terms-of-speed-congestion.pdf which states that “Current average traffic speeds in central London are around 14 kph, in inner London about 20 kph and those in outer London vary between 30 and 35 kph. The overall trend is one of marked stability over the most recent six years.”
I took the lower of these ( 30kph )and took a two km journey giving 4 minutes. As you say these are journeys “up to” two km so in reality the average saving would be less than this but I kept it at 4 mins (in your favour) for ease of maths.
The point of the post is the inability of the schemes to reduce pollution. I gave you a best case scenario and even if people amazingly did not take back to their cars (which a proportion certainly would) there will still be an increase in pollution if the remaining traffic has to take a longer journey or is sitting in congestion which increases their journey time by more than just one minute. The congestion also concentrates the pollution as more is exhausted in a local area and this queuesmog is not dispersed as the traffic is not moving.
A 20 car per 100 would be an amazing achievement. Even the Walthamstow Village scheme only claimed a 16% reduction but we both know the calculation of this was immensely flawed. I am happy to show you in open discussion here if you want to engage in that.
I agree that the Google and Waze apps have made things easier to find alternative routes but again the 72% figure you quote is highly debateable, stemming from the 2018/19 one off Minor Roads Benchmarking Survey which adjusted ten years of accepted traffic flows upwards by 20+%. Again I am happy to debate here the flaws in this adjustment. You only need to look at the sentence above from TfL “The trend is one of marked stability over the most recent six years”. Traffic flows go up 20+% but the speed of the traffic on a fixed road network is unaffected ? Really ?

I'm not a mathematical/statistical modeller but the other significant variable missing from your analysis is the effect of the ltns on people making longer journeys - whilst they may not walk or cycle many will decide the journey they used to make through an ltn is no longer worth it - they'll take public transport, not make the journey or fulfil the need closer to home. The Fox Lane ltn has taken a significant mileage out of the through road network - it was used by thousands of through drivers every day (the figures can be found elsewhere on this site). I can't believe all of those are now on the peripheral roads. Let's see what the pre and post traffic counts say when Enfield Council conduct and publish them. I think you'll be surprised at how the total traffic movements including the peripheral roads has fallen. The protestors talk of 24/7 gridlock and post videos on social media showing endless queues, yet I can see Alderman's Hill, not far from the Triangle, from my house and its invariable free - the stats will tell us who is right. In the interim around 3500 households in the trial Fox Lane LTN are enjoying lower levels of atmospheric pollution, noise pollution and safer streets .

But to my knowledge there were no precounts (or measures of pollution) before the trial on the peripheral roads. If there were could you please forward these or advise where I can find them?

There are complaints coming in from roads that are further afield such as Wynchgate, Morton Way, Forestdale who have all had additional traffic diverted their way. Were these measured for counts pre trial or indeed be counted post trial? In a similar way to the Walthamstow schemes, traffic diverting slightly further afield is just ignored and counted as evaporation ?

The people you refer to as not making the journey or fulfilling the their needs closer to home are already accounted for in the 20 cars removed. That's why they are removed. It doesn't address the maths of increased pollution. I'm not a statistical modeller either. I'm a decorator, but this is just basic stuff.

Following the posts I’d be left to conclude that if taking a full 20% of road journeys off London’s streets still results in no effective reduction in the air pollution, gases and particulates, that is shortening all of our lives and causing wide ranging damage to our heath - and has been for decades - then more than the expected patchwork of LTN’s and other current traffic inhibiting / active travel supporting plans is required.
The Polluter Pays Principle, effectively the legal issue at the heart of Georgina’s incinerator case vs HMG posted elsewhere on the site, has long been bypassed when it comes to road travel. Sit in your armchair looking through your widescreen and those all about pay a price. LTN’s aren’t the issue; we all need to focus on the actual cause and amend our behaviours.

There's several counts available on this site (some link examples below). I don't know if/when pollution was measured but volume of traffic is a pretty good proxy. I don't know if roads not shown in these tables were counted (its likely as the Council do a lot of traffic counting), but the good news is that in time many of those roads you mention will be included in the planned network of LTNs in Enfield, so will also see traffic and pollution reductions. Connaught Gardens will be next and Haringey has just announced a 'south Bowes' LTN to abut Enfield's trial LTN. And of course whilst LTNS do reduce pollution there are many other advantages that have been well rehearsed on these pages - and here www.betterstreets.co.uk

https://www.pgweb.uk/planning-all-subjects/quieter-neighbourhoods/2163-fox-lane-area-traffic-counts-and-speed-data

https://www.pgweb.uk/images/2019/documents/Fox-Lane-Monitoring.pdf

Adrian and Karl. Firstly I would like to thank and congratulate you for actually engaging in a debate and not simply shutting down the thread as has happened to many people on many sites. I also believe you are both genuinely coming at this from a point of view of wanting to improve things for lives of local residents. I for my part am supportive of making things safer for cyclists and walkers. I agree with putting in cycle lanes where they are reasonable. The Green Lanes scheme could have been generally highly acceptable to the community if it had not had the ulterior motive of deliberately trying to reduce traffic flow to force traffic off the road. The bus stop design alone is testament to this. The point of my posts is that the LTNs are not going to work with respect to pollution, they almost certainly will increase it.
I note that neither of you have countered the mathematical argument. Karl, you seem to be saying in your first paragraph in #5811 is if LTNs dont work in reducing pollution then lets have more of them. A strange logic. I will happily suggest to you alternative schemes that would have an effect on pollution but to continue on compounding the same mistake seems a strange notion. You also say "LTNs aren't the issue" well at the moment, here and now, they are the issue and they are dividing the community.

Adrian both the links of data counts you give are for the internal roads of the LTN which I have seen from links on this site before. I am looking for data counts ore LTN on the perimeter roads Bourne Hill, Aldermans Hill , Cannon Hill / Southgate High Street , Green Lanes. Does anybody have these ?
The link to Better Streets links me to one of those sites that will not engage in debate so their "well rehearsed" arguments cannot be countered. I will happily post here how their calculation of 16% evaporation of traffic from the Walthamstow Village scheme is a myth. How the apparent 20+% increase in traffic flow over the last ten years did not exist just two years ago but that all the data files for the last ten years at the Dept. of Transport were all changed due to a single dubious survey carried out in 2018/19. How the much quoted Greenpeace/ YouGov poll spun by Peter Walker in the Guardian is so flawed and meaningless that even Greenpeace don't quote it. How most of the surveys showing support for LTNs are bland questioning aimed at getting support whereas when you survey people who are actually living with the experience of even " bedded in" schemes are heavily opposed to them, such as the TfL survey of the Railton Road scheme.