Evaporating traffic? Impact of low-traffic neighbourhoods on main roads


By Emma Griffin, vice-chair, London Living Streets

Low-traffic neighbourhoods can be life-changing for the residents who live in them. Since the neighbourhood improvements in Walthamstow Village in 2015, people are walking and cycling more, children play out, air pollution has improved and life expectancy increased.

But bold traffic plans such as this are often introduced amid concern and opposition. This series of blogs explores these questions and presents research that helps fill missing gaps and tackles any misunderstandings.

Here we examine concerns that low-traffic neighbourhoods may divert traffic onto main roads leading to increased congestion and air pollution.

More information on what low-traffic neighbourhoods are and how they work is available here. Find out how many low-traffic neighbourhoods there are in your area on the London Boroughs Healthy Streets Scorecard here.

Traffic evaporation 

Experience reveals that predictions of traffic problems caused by low-traffic neighbourhoods almost always fail to materialise, and that significant reductions in overall traffic levels across an area can happen as a result of people making a wide range of behavioural responses to the new traffic configurations.  

The most comprehensive study of the phenomenon of disappearing or “evaporating” traffic was carried out by Sally Cairns, Carmen Hass-Klau, and Phil Goodwin in 1998 and followed up in 2002. See below and here.

This brought together experience from 70 case studies of roadspace reallocation from general traffic, across 11 countries, with opinions from 200 transport professionals. It shows that traffic does not behave like water moving through pipes, finding an easier path as another narrows. Instead it is a force of human choice, driven by people making all sorts of different decisions when driving conditions change. The respondents in the Cairns study, for example, changed their mode of travel, chose alternative destinations, or the frequency of their journey, consolidated trips, took up car sharing or didn’t make the journey at all.

In half of the case studies, there was a 11% reduction in number of vehicles across the whole area where roadspace for traffic was reduced, including the main roads.

This research shows that low-traffic neighbourhoods do not simply shift traffic from one place to another, but lead to an overall reduction in the numbers of motor vehicles on roads. In Waltham Forest this meant there were considerable reductions on streets within the neighbourhood – some streets have seen 90%+ reductions in motor traffic and 56% on average. On the surrounding roads there have been increases, but they have not taken all the displaced traffic. More here.

More people walk in low-traffic neighbourhoods 

What’s really encouraging, is that one of the most significant behaviour changes following implementation of low-traffic neighbourhoods has been a shift to more walking and cycling.

Just one year after the implementation of  schemes in Outer London, including Waltham Forest, residents were walking 32 minutes and cycling on average 9 minutes more per week. This ongoing London School of Hygiene & Tropical Medicine and University of Westminster study is available below and here.

As Rachel Aldred, reader at University of Westminster and one of the study’s authors says, “new infrastructure often takes some time to have an effect on active travel, but in this case we are seeing positive results after only one year”.

This demonstrates that if councils improve the conditions for walking and cycling (and make driving just a little more inconvenient), people take the bait very quickly. And as time goes on, as active travel becomes embedded in lifestyles, more will follow leading to long-term change over an entire area.

Shrewd city planning

Low-traffic neighbourhoods are not, therefore, about rewarding one group of people while punishing another: they are part and parcel of shrewd city planning, making long-term decisions about how people travel.

And the potential for change is massive: currently around 1.6 million, or 22%, of all car trips made by London residents every day are under 2km and could therefore be walked (2.7 million more could be cycled). See below and here.

Any measures for converting these car journeys to active modes should be of paramount importance for London boroughs – not just to reduce traffic volumes but to improve the health of communities through activity and lower air pollution.

A 2018 study by King’s College London (more below and here) linked the boost in active travel in Waltham Forest’s low-traffic neighbourhood with increased life expectancy as a result of improved air quality, increased activity and shift to active travel on the school run.

This research also found that more than 51,000 households in Waltham Forest are no longer living in areas with dangerously high levels of air pollution compared to a decade ago.

Impact on main roads

So what about the main roads? Even with traffic evaporation, main roads will shoulder some extra traffic. But evidence suggests the impact of this isn’t as big as some fear.  Waltham Forest’s research shows that bus journey times (on main roads) have not significantly increased following introduction of LTNs.  That research is available here, chapter four.

King’s College London research, based on modelling work where traffic volume is used as one of the inputs to determine air quality, suggests that there has not been a decrease in air quality on main roads following introduction of LTNs. That report is here, page 8-9.  

Main roads were also designed to take the majority of traffic, so can absorb increases in traffic better than their residential counterparts. These streets have wider carriageways, with buildings set further back. They also have better crossing facilities and safer junctions.

A small increase in traffic on a main road is also less noticeable than the transformation brought about by a dramatic reduction on a residential street: of a child riding a bike to school, of walking to the local shops, or hearing birdsong again. And given the majority of people in London live on residential streets, these sorts of improvements could be life-changing for millions.

For an illustration of how non-local traffic can degrade the environment and safety of residential roads, watch this video Stoke Newington, London. https://twitter.com/mum_on_bike/status/1138444799139356683

Counts on main roads in Waltham Forest also showed that traffic was more spread out across the day following introduction of the low-traffic neighbourhoods. In fact, maximum peak hour flows were lower on the main roads. More here. In other words, the traffic Armageddon that some expected never arrived.

All that said, any increase in traffic is hard to accept if you live on a main road or send a child to school there. As a result, main roads also demand urgent attention.

Action for main roads

One solution, being adopted in many cities across Europe and in Britain (for example in Glasgow), is to reconfigure main roads as urban “boulevards”. London also has the benefit of the Healthy Streets Approach to help deliver this sort of change. Urban boulevards could feature, for example:

  • wider, better pavements;
  • lane reductions;
  • removal of parking;
  • bus lanes;
  • cycle tracks;
  • speed restrictions;
  • more crossings;
  • more seating, trees, and planters; and
  • closed side streets and banned right turns to increase capacity and reduce congestion and air pollution.

Wider road traffic reduction policies are also necessary and increasingly possible, including:

  • workplace parking levies;
  • parking restrictions; and
  • a 24/7, London-wide, distance-based road user charging scheme, now on the cards for the longer term. Read Centre for London’s report on Next generation road user charging here.

These wider policies, plus redesigns of main roads and low-traffic residential schemes should all be addressed in unison, even if they are delivered over different timescales.

Doing nothing is no longer an option

The alternative — of proponents of different approaches falling into opposing camps – will only result in inaction, or watered-down schemes and lengthy delays. And there isn’t time for this.

London’s population is set to grow from around 8.6 million today to 10 million in 10 or so years. There simply isn’t space for all these people to fit in cars on roads. Climate change, air pollution and the health impacts of inactivity are also at crisis point, requiring immediate and drastic action. As the research listed here demonstrates, low-traffic neighbourhoods are one of the easiest, quickest and cheapest ways to take on this challenge.

Useful research

Check out how many low-traffic neighbourhoods there are in your area on the London Boroughs Healthy Streets Scorecard. https://londonlivingstreets.com/2019/07/15/new-scorecard-reveals-gaps-in-london-boroughs-progress-on-healthy-streets/#more-1846

Traffic evaporation

Disappearing traffic? The story so far. S. Cairns, C. Hass-Klau, and P. Goodwin. “Predictions of traffic problems are often unnecessarily alarmist, and  .. given appropriate local circumstances, significant reductions in overall traffic levels can occur.”  https://nacto.org/wp-content/uploads/2015/04/disappearing_traffic_cairns.pdf

When roads are closed, where does the traffic go? Braess paradox, Dietrich Braess. Adding extra capacity to a network may reduce overall performance and increase travel times. As in a game structure, if drivers have the possibility to choose their own route autonomously, they will behave selfishly. This means that each driver will aim at improving its respective travel time by arriving first: all drivers will take the new “fast” road and will thus cause congestion.” http://h2020-flow.eu/news/news-detail/when-roads-are-closed-where-does-the-traffic-go-it-evaporates-say-studies/

A great case study of traffic evaporation from New York City. Cars Were Banned on 14th Street. The Apocalypse Did Not Come, The New York Times.

Impact of LTNs on traffic volumes and active travel

Comparison of average daily vehicle numbers from 12 roads within the Walthamstow Village area before and after the 2015 trial and after the work took place. Overall there was a 56% reduction in traffic across the whole area.   https://www.enjoywalthamforest.co.uk/work-in-your-area/walthamstow-village/comparison-of-vehicle-numbers-before-and-after-the-scheme-and-during-the-trial/

1.6 million car trips per day, made by London residents, could potentially be walked (22% of car trips). Potentially walkable trips are defined as shorter than 2km; made between 6am and 8pm; made without a heavy or bulky load; made by someone aged 5 to 74 without a disability; and exclude trips made by van, dial-a-ride, plane and boat. https://www.london.gov.uk/sites/default/files/health_impact_of_cars_in_london-sept_2015_final.pdf

Longitudinal study co-authored by the London School of Hygiene & Tropical Medicine (LSHTM) and led by the University of Westminster.https://www.lshtm.ac.uk/newsevents/news/2019/transport-londons-mini-holland-programme-associated-more-walking-and-cycling

Impacts of low-traffic neighbourhoods on air quality, health, well-being and safety

The benefits of routine walking and cycling activity is estimated to gain around 204,000 life years (a life year is one person living for one year) for the population over a lifetime. This represents an increase in life expectancy of between seven to nine months for everyone in Waltham Forest (based on the current population). Waltham Forest study of life expectancy benefits of increased physical activity from walking and cycling, for Waltham Forest local authority by King’s College London https://drive.google.com/file/d/1BqGRWsN17qZNbvuqrMARql1QYu3_M7Rd/view

More than 51,000 households in Waltham Forest are no longer living in areas with dangerously high levels of air pollution compared to a decade ago. https://www.enjoywalthamforest.co.uk/blog-post/independent-studies-find-people-are-living-longer-and-getting-more-exercise/

Waltham Forest has used 49 NO2 diffusion tube sites to compare exposure to NO2 between 2007 and 2017 and found the number of households exposed to more than the EU recommended maximum amount of Nitrogen Dioxide has dropped dramatically, from 58,000 in 2007 to just 6,300 in 2017. https://walthamforest.gov.uk/sites/default/files/Population%20Exposure%20Comparison%20F1.pdf 


Waltham Forest commissioned King’s College London to model the impacts of recent road interventions in the borough on air quality. The report found that that measures to prioritise pedestrians and cyclists such as segregated cycle lanes, increased pocket parks and timed road closures had made a marked contribution to improving air quality and health in the borough
The King’s College London air quality report
The King’s College London health benefits report

Physical inactivity directly contributes to 1 in 6 deaths in the UK and costs £7.4 billion a year to business and wider society. Building walking or cycling into daily routines are the most effective ways to increase physical activity. https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/523460/Working_Together_to_Promote_Active_Travel_A_briefing_for_local_authorities.pdf

Commuting by car is associated with low social participation and low general trust compared with active commuting https://journals.sagepub.com/doi/pdf/10.1177/0013916514529969

Commuting affects your mental health, your physical health, and even the way you think about other people. And these changes are more profound than you might think. https://gizmodo.com/the-best-ways-to-get-to-work-according-to-science-1733796033

Fears over road safety act as a persistent barrier to walking and cycling, according to 2015 study by road safety charity Brake. http://www.brake.org.uk/news/1369-walking-cycling-jan15

Children in deprived neighbourhoods are most likely to be involved in road accidents. The report argues that Government should concentrate on making streets safe and liveable for children and worry less about whether they are perceived as pro- or anti-car. https://www.ippr.org/publications/streets-ahead-safe-and-liveable-streets-for-children

Road transport alone contributes about one-fifth of the EU’s total emissions of carbon dioxide (CO2), the main greenhouse gas. https://ec.europa.eu/clima/policies/transport/vehicles_en


8 Replies to “Evaporating traffic? Impact of low-traffic neighbourhoods on main roads”

  1. The optimism is complete nonsense. I live off Nightingale Lane and over the last few days roads have been shut and chaos has ensued. I have lived here for over 20 years and have never known traffic jams like it. Ni diversion signs are in places, seemingly roads have been shut for no apparent or logical reason. It is already a nightmare and many people are actually on holiday. What it will be like soon I dread to think.
    We dont all want to walk or cycle, some of us need to get about in our ecological cars. I need to drive, I am 78 and very active. but cycling is a complete no-no..
    There was very little warning, and it has just made matters worse in areas where there were few problems beforehand.
    I really think weshould have some say in our neighbourhood.


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