Forum Topic

Traffic Evaporation

https://www.rapidtransition.org/.../reducing-roads-can.../https://thecityfix.com/.../traffic-evaporation-what.../Jevons paradox: https://www.youtube.com/watch?v=sTE4H-2oecY...Braess paradox: https://www.youtube.com/watch?v=RmLrpci_tfo...Downs-Thomson paradox: https://www.youtube.com/watch?v=RQY6WGOoYis...

Hans Lund-Sorensen ● 1859d31 Comments

A valiant attempt Hans but this isn't the forum for people who want to learn.

Paul Campbell ● 1858d

Personally highly disinclined to open a load of links in a post that doesn't even carry a brief description of what you're selling or why i should click on them. So i guess i shall never know!
Here is a link to dogs in funny halloween costumes. Seasonally relevant: https://www.thepioneerwoman.com/holidays-celebrations/g33383101/funny-dog-halloween-costumes/?slide=8

Rob Reynolds ● 1858d

Hans, I'm interested, but any chance you could give us a one line summary of each one?

Simon Pedley ● 1858d

RR:"Personally highly disinclined to open a load of links in a post that doesn't even carry a brief description of what you're selling or why i should click on them." I clicked on the last of the links (only) and it was a very informative 6 minute video explaining the Downs-Thompson paradox i.e. if you want cars to travel quicker in cities, you actually need to give MORE road space over to public transport, cyclists and pedestrians instead, not less.https://www.youtube.com/watch?v=RQY6WGOoYisOf course this is counter-intuitive, but the examples given from Canada, Japan, France, Netherlands etc are compelling.HTH.P.S. I shall pass on your 'dogs in costumes' video, if you don't mind.

Richard Cathcart ● 1858d

The original research of this was done in 1997 and updated in 2002 (S Cairns) and was far more nuanced that subsequent coverage which simply took the research and stripped out the nuance.The authors of the research explicitly stated that "in some circumstances overall traffic levels in the local level may reduce..."They did not say it would always reduce and they were very careful to emphasise that it was at the local area level.The research is well worth a read but only if you take into account the nuances and caveats that the authors stated.  It is completely clear that a well designed and carefully implemented scheme (which rules out a lot of LBH ideas) can and usually does reduce traffic in the local area typically by 11-14% but it is a lot less clear, in part because it is very difficult to study, how much of this evaporated traffic has simply moved to journeys away from the local area.Applying this to the LBH schemes is hard because it is far from clear whether LBH have considered the cumulative impact of all the various proposals

Justin Stephenson ● 1858d

Thanks for the links Hans.  All very interesting and informative.  Many of the observations at first glance would seem counter intuitive, but on reflection make much sense.  For example, make public transport quick and easy, and people will migrate from private cars until there is an equalibrium between the time taken to make the journey in car vs public transport.It would be great to see a hypothecation of the revenues raised by the LTNs to be reinvested in public transport schemes.  It might make any perceived disadvantages less of a bitter pill to swallow.

EH McNeill ● 1857d

"It would be great to see a hypothecation of the revenues raised by the LTNs to be reinvested in public transport schemes."Agreed. These funds should also be spent on active travel and public realm improvements. Turning ugly barriers into mini-parks and planting lots of trees in areas where traffic reduction has been substantial.You are right about how counter-intuitive the phenomenon of traffic evaporation is. It is why we see so many people scoffing at the concept. But it is actually proven time and time again in practice in locations all over the world and it is fundamental to the policy of reducing traffic, which is why it has been adopted by the government.

Paul Campbell ● 1857d

Thanks for the links Hans, I'll try and work through them. My own view is that the idea of traffic evaporation is based on a logical fallacy and the research I've read on it before only seems to indicate the phenomenon occurring in areas in which it is part of a broader strategy particular improving public transport.Whether it could work in Chiswick right now is very debatable. About a year back in response to another thread on here I looked more closely at the statistics on vehicle movements in the area. Using Department for Transport figures for the breakdown of motor traffic on Chiswick High Road and the TfL guidelines for what journeys could be walked or cycled rather than driven, the numbers suggest that 7% of vehicle movements were car journeys that potentially be walked and 18% were car journeys that potentially could be cycled.In working out these numbers I erred on the side of conservatism i.e. I made assumptions that ensure they were as high as possible for instance taking the lowest of the ONS's range for the proportion of car journeys that are made by private hire vehicles.Although 7% and 18% might be seen as reasonably proportions to work with these would still include car journeys made for commercial purposes or to provide services and a substantial number of them are unavoidable for justifiable reasons e.g. the driver or one of the passengers is elderly or disabled or something that is too heavy to carry is being transported.It's a guess but if you account for all these factors then you could say that 3% of vehicle movements could practically be walked and 9% could practically be cycled.  Given the challenge of converting these journeys to be made by active travel means and that by definition they are short so the benefit of conversion will be far less than if you got people taking longer journeys to convert,  the potential for modal shift from cars to walking and cycling is quite limited.What the studies clearly show is that public transport should be at front and centre of any strategy as that has the potential to remove longer and therefore more impactful journeys. Unfortunately right now we are on the cusp of some very significant rises in public transport fares and cuts to services for both trains and buses.Even if the active travel measures in the Chiswick area were encouraging traffic evaporation, which I doubt, the impact is going to be overwhelmed because more people will be driving because public transport has become more expensive and less reliable.In addition we are going to see very large population increases on the periphery of our area including the Brentford stadium development which will start to be occupied later this year and the massive Bollo Lane schemes which collectively could add around 15% to the local population.Consequently I think the last thing we should be doing at the moment is closing roads in the area in the forlorn hope that traffic will magically disappear.

Jeremy Parkinson ● 1856d

You’ve either misread or miscalculated the figures.  I wrote this earlier.  During lockdown traffic decreased as people reduced their travel to the bare necessity. Nationally, vehicle numbers dropped dramatically to 31% of pre pandemic levels. But in London, the drop was even greater to just 15%. Of course that was under extreme conditions, but nevertheless it does indicate that there is a higher proportion of discretionary travel in London than nationally.This ties in with other data. There are more cars on London's roads at the weekends than during the week, and a third of car trips are under 2 miles. A high proportion of these trips could indeed be made by most people by walking or cycling rather than by car.At the moment traffic seems to be mainly condensing on petrol-station forecourts.

Tom Pike ● 1856d

The 2 miles trips could be for heavy shopping they are unable to carrypossibly the elderly and disabled, mums with children, need to calculate how many of the drivers are dependent on a vehicle instead of suggesting they cycle.

Janice Evans ● 1856d

Where does the myth of the 2 mile/2k journey come from. Data thought up by the cycle lobby I think. I say the same thing every time. No one knows where I’m going or how far and everyone  says the same. Just because  you said it doesn’t make it true. Just look at Will Normans stats.

Maggie Dodge ● 1856d

I have a question.Is this two mile figure based on a journey simply from A to B? ie one movement.If so then is it not the case that the vast majority of trips must return to a starting  point therefore be four miles overall?

Adrian Irving ● 1855d

I think it’s a non story.  I wouldn’t  waste time trying to figure it out. The cycle lobby groups are a bit like a cult. You’ll find they all spout the same stuff. I think it’s in the handbook. Converting others too. You get a new set of cycle clips for each new convert apparently. I hear branches of the LCC are called Chapters, is that like Hells Angels ?

Maggie Dodge ● 1855d

The figures come from the National Travel Survey which is conducted by the Department for Transport. Policy should be informed by evidence like this rather than based on unsupported opinion.

Tom Pike ● 1854d

Posted on Facebook The car-free myth. The Netherlands is a great country to live in if you're car-free, but it's a very long way from being a car-free country. Dutch car ownership and use are at an all time high.cycling is going down

Maggie Dodge ● 1854d

Just for the record. In a list of car-ownership per capita the UK ranks 34th at 473 per 100.000 of population. The Netherlands comes in at 30th with 499.

Bruce Hammal ● 1854d

Tom, if I were you I'd wouldn't post about your theory that the fall in traffic during lockdown proves evaporation works. People are relatively kind and respectful one here compared to other places on the internet and you would be subject to some quite hurtful comments.On the stats I can assure you that the numbers I have used have all been sourced from official sources. There is not necessarily an inconsistency between your figure and mine as you are referring to car journeys in general whereas mine relate to motor vehicle journeys in Chiswick in particular.Bruce raises a very important point. In making my calculations I am assuming that TfL worked out their numbers based on the total trip i.e. not splitting the outward and return journeys. If they did count these as two trips this would halve the number of motor vehicle journeys that is was possible to walk or cycle to 3.5% and 9% respectively. The number that it was actually practical to walk or cycle would be a fraction of that.I asked TfL to clarify this point when I was working out the numbers but they never responded.

Jeremy Parkinson ● 1854d

If you used the traffic counts of bikes and cars along the High Road, then you had no data on the trip length to be able to assess the possible modal shift. In any case, your numbers are clearly off as bikes are now amounting to 20% of the traffic on the High Road compared to 15% in the 2018 counts. Both are way above your estimates of the possible trips that could be walked or cycled.

Tom Pike ● 1854d

As no one has commented on my previous question I think the much quoted two mile average journey is just from A to B and does not include the B to A.Statistics need to be cross examined particularly when they are contrary to by people's experience and on the ground obsevations.

Adrian Irving ● 1854d

I used figures provided by TfL to determine the proportion of trips that could be possibly walked or cycled.The proportion of trips currently being taken by cyclists isn't relevant to my point and if they were included in the analysis would decrease the potential of journeys that could be shifted. What I am trying to pin down is the proportion of motor vehicle journeys in Chiswick that could be switched. I came up with figures of 3.5% for walking and 9% for cycling.The methodology was to take the proportion of journeys by motor vehicle type for Chiswick High Road from DfT figures - Adjust down the proportion of cars to account for the proportion of private hire vehicles using the lowest end estimate from the ONS - Use data given by TfL on the proportion of car journeys in London they believed could be either walked or cycled - Halve that number to allow for private cars being used as commercial for other services purposes, trips by the elderly, disabled or where the car was needed to carry something heavy.If you want to dispute the numbers redo my calculations or come up with a methodology you think is more appropriate. Remember I've assumed that TfL was looking at both outward and return journeys when giving their figures, if not my numbers would need to be halved again.Even with the larger number, the proportion of potentially substitutable journeys is very low.

Jeremy Parkinson ● 1854d

TfL analysis into potentially cyclable trips already takes into account trips that aren’t cyclable based upon a set of criteria (some of which are arguable, for example, they exclude everyone over 64).It looks like your methodology is flawed if you are taking the TfL cyclable estimates then adding on your own opinion of additional non-cyclable trips. This is double counting  non-cyclable trips.

Michael Robinson ● 1854d

Nope - the figures I used from TfL were exactly as stated - the proportion of trips under distances which they believed could be walked or cycled. As mentioned previously I did ask them questions about the way the numbers were calculated but there was no question of them excluding people over 64 which, if is that what they do in other instances, is ridiculous.

Jeremy Parkinson ● 1854d

TfL's analysis has been updated: their latest estimates of cyclable trips use a progressive reduction in trip size for over 64's. They also exclude trips for all ages if they are more than 8 km (10 km for commuting) and if they are transporting tools, heavy work equipment, or a pram/pushchair.They found on that basis that of the 20m trips Londoners make a day, 8m could be cycled. If London were to realise this potential, more than two thirds of car trips would be eliminated with 15,600 more trips a day to or from Chiswick being cycled. content.tfl.gov.uk/analysis-of-cycling-potential-2016.pdf

Tom Pike ● 1854d

Sorry, should have been more precise.  TfL exclude trips over 8km (or 10km if commuting) made by people over 64.The point still stands that your approach is incorrect.  You are taking a figure that already factors in non-cyclable trips and you then include your own opinion of non-cyclable trips that have already been considered.You don't appear to have read the Analysis of Cycling Potential document that explains the methodology used to calculate cyclable trips which, by definition, uses the criteria for non-cyclable trips.

Michael Robinson ● 1854d

And none of this includes the rain......

Bruce Hammal ● 1854d

Cycling numbers vary by 20% over the seasons in London. Motor traffic varies by 10% seasonally, so not much of a difference.

Tom Pike ● 1854d

My number varies by 100%. I never cycle in the rain.It's a thoroughly unpleasant experience and I just don't look good in a cycling cape. With all that government money maybe we could get the cycle lanes roofed in. What about poly tunnels?

Bruce Hammal ● 1854d

There’s some rather more elegant options than a cape available these days. You could weigh them up against the unpleasant experience of spending too much time at the petrol station.

Tom Pike ● 1854d

I don't have a car any more. My wife does though and I occasionaly borrow hers for stuff I can't carry or get on the bus without causing disruption.  I did once manage half a sheet of plasterboard on the 272....

Bruce Hammal ● 1854d

Glad to hear you’re not having to join the melee, Bruce!

Tom Pike ● 1854d

There has been a big push in the Netherlands to return to its greater cycling.  They found that children who were exposed to cycling earlier in their lives were safer on the roads because they gained much better road sense.

Philippa Bond ● 1853d