Roadworks, Air Quality and Disappearing Traffic

Picture of Gosforth High Street showing Trinity Church

In our last blog we shared the results of the 2017 Council air quality monitoring, showing that Gosforth High Street had the highest recorded nitrogen dioxide (NO2) air pollution in the whole of Newcastle.

In this blog, we take a look at three key questions that came up in discussion following release of the 2017 air pollution figures. These questions are:

  1. Why has air quality on Gosforth High Street deteriorated?
  2. Does restricting traffic flow cause more pollution?
  3. What happens to traffic when roads are shut?

The better understanding we collectively have of the answers to these questions, the better chance there is to bring pollution down to legal limits as soon as possible.

1. Why has air quality on Gosforth High Street deteriorated?

The government estimates that 80% of roadside air pollution is generated by vehicle traffic so, even without looking at any data, it is reasonable to suggest that vehicle traffic has been the source of the additional pollution. The question then is whether the increase has been due to more traffic, or because traffic has been held up and is waiting longer and emitting more while it is waiting.

We do have some data that can help us to answer this. In the graph below the two lines represent average daily vehicle volumes on Gosforth High Street  (red line / right axis) and air pollution (blue line / left axis) between January 2016 and December 2017. Each point represents the average of two months. The gap in the red line is because we don’t have vehicle volumes, measured by The Grove, for either January or February 2017.

Graph of air quality and vehicle volumes on Gosforth High Street showing a strong correlation between the two.

It is pretty clear that the more vehicles there are on Gosforth High Street the worse the air pollution is, as the two lines follow each other quite closely, and that the increase in air pollution in 2017 compared to 2016 is almost certainly a result of more traffic using the High Street.

It is also clear that in both 2016 and 2017 air pollution was significantly worse than the legal limit of 40μg/m3 NO2 averaged over a year. We don’t have data for pollution at this location prior to 2016, as 2016 was the first year air quality was measured in this location, but based on vehicle counts we can be reasonably sure air quality wasn’t any better prior to 2016 as traffic levels have been declining on Gosforth High Street since 2010.

Diesel buses are often mentioned as a specific cause of pollution on the High Street and we hope that low-emission buses will form part of the Newcastle City Council Air Quality Plan due early 2019.  This data suggests however, that having cleaner buses may not be sufficient by itself to resolve air pollution concerns on Gosforth High Street, as pollution was worse after August 2016 even though Arriva had introduced new cleaner buses about that time.

2. Does restricting traffic flow cause more pollution?

The Government’s 2017 Draft Air Quality Plan suggested “Improving road layouts and junctions to ‘optimize’ traffic flow” as a way of tackling air pollution. Improving traffic flow and reducing pollution were also described in the Council’s 2014 Air Quality Progress Report as objectives for the Salters Road / Church Road junction. 

In the SPACE for Gosforth response to the Government’s Air Quality Consultation we asked that the the Government prioritise the most effective measures to reduce pollution, which according the Government’s own assessment did not include optimising traffic flow. The Government’s final plan acknowledged that there is “there is considerable uncertainty on the real world impacts of such actions“. This is because rather than reducing air pollution, changes that are designed to improve or optimise flow can lead to more traffic (and more pollution).

We can use the same traffic data to see what the effects were of the roadworks at Salters Road junction between about February and August 2016, and the effect of Killingworth Road being closed to traffic from July 2017.

This next graph shows week-day traffic in 2016 and 2017 compared to the average for the same month between 2013 and 2015. The dotted lines indicate months in which traffic was measured on fewer than half of the days in that month.

Graph of vehicle volumes on Gosforth High Street in 2016 / 2017 compared to the 2013-2015 average.

During the Salters Road junction roadworks (March-August 2016), when traffic was controlled by temporary traffic lights, there were 1032 fewer vehicles per day on average compared to 2013-2015.

During the second half of 2017, at the start of the Killingworth Road roadworks, the Council’s mitigation included “Timings on traffic signals on key routes programmed for longer green lights on routes that will see extra vehicles during peak periods” i.e. enabling more north-south traffic flow. During this period (August, October, November, December 2017) there were 1240 additional vehicles per day on average compared to 2013-2015. We have excluded September 2017 from this average as traffic volumes were counted on fewer than half of the days in September.

So when traffic was constrained (via roadworks) there were fewer vehicles and lower pollution, and when Killingworth Road was closed, and there were longer green lights for north-south traffic on the High Street, there were more vehicles and more pollution. It appears that rather than causing more pollution, the 2016 roadworks had the opposite effect and actually reduced pollution on Gosforth High Street.

To know whether the Killingworth Road effect is due to the mitigation that increased flow or due to rerouted traffic we need to answer our third question.

3. What happens to traffic when roads are shut?

In our blog about the Killingworth Road Metro Bridge Replacement from Jun 2017 we included this map below. In it we highlighted The Great North Road and Benton Lane as roads to avoid during the works as we thought these were most likely to be impacted by traffic re-routing as a result of the Killingworth Road closure.

Map of the north of Newcastle showing the Killingworth Road closure, routes that might be impacted as well as park and ride sites.

Traffic volume data is available for these routes so we can now see what that impact was. This shows that the average weekday traffic volumes for The Great North Road and Benton Lane were almost exactly the same in the second half of 2017 as they were in 2016. i.e. there was no additional traffic on these routes when Killingworth Road was shut.

Location July – December 2016 July to December 2017 Change
Great North Road (north of Hollywood Avenue) 28,298 28,218 -80
Salters Lane (Killingworth Road) 17,064 4,636 -12,428
Benton Lane 22,074 22,001 -73
Total (average weekday traffic) 67,436 54,855  -12,581

Even if the extra thousand vehicles on Gosforth High Street are a result of the closure, despite traffic levels on the Great North Road were unchanged, that is still a significant reduction in overall traffic levels.

This is almost certainly an effect called Disappearing Traffic where, contrary to what most people might expect, reducing road capacity can lead to substantial reductions in overall traffic levels.  Studies of Disappearing Traffic confirm that this doesn’t necessarily mean that people are travelling less, just that people have a range of choices for how and when to travel.

On Station Road there is a similar picture. Weekday traffic in the second half of 2017 is higher than previous years but by far less than you would expect if all 8,000+ vehicles previously using Hollywood Avenue had re-routed via Station Road, and not substantially more than it was 2013 or 2015.

Graph of vehicle volumes on Station Road from 2013 to 2017.The dramatic drop in traffic in September 2016 may be because of roadworks by Northern Gas Networks on Station Road. If so, it would be another example of constraining traffic flow leading to fewer vehicles and less pollution (25% less in September than the 2016 average).

Despite vehicle numbers in 2017 being higher than 2016, air quality measured on Station Road in the second half of 2017 was better (35.3μg/m3) compared to the same six months in 2016 (41.9μg/m3). This is most likely because the closure of  Killingworth Road has meant far less traffic on Haddricks Mill roundabout.

Reducing Air Pollution

The data presented above suggests pollution is linked more to traffic volumes than flow, that constraining traffic leads to better air quality, and that closing Killingworth Road hasn’t made any great difference to traffic on The Great North Road or Benton Lane.

That’s not to say Killingworth Road has had no effect. For some people journeys will be worse, and others e.g. those that drive East-West across Haddricks Mill or use the 33 bus on Hollywood Avenue, which is no longer delayed by through traffic, will have better journeys.

It does mean we should be concerned by measures attempting to improve air quality by improving traffic flow, as they might just make it worse. The most effective way of reducing air pollution, according to the Government, is to introduce Charging Clean Air Zones (CAZ). These work by charging for, and therefore discouraging, trips made by the most polluting vehicles.

Newcastle City Council only has one month left to complete its plans to bring air pollution on Gosforth High Street and across Newcastle within legal limits in the shortest possible timescales. We don’t know for certain what this will involve but almost certainly it will need to include some sort of restriction on traffic if it is to have any measurable effect.

Notes

  • Air Pollution Data is taken from Newcastle City Council’s annual monitoring reports using measurements taken on Gosforth High Street just south of Woodbine Road.
  • Data on traffic volumes is from the TADU website. Gosforth High Street measurements are from near The Grove.
  • We don’t have data for traffic queue lengths or journey times so don’t know how those have been affected, although it is a reasonable assumption that more vehicles using the Great North Road after the Salters Road junction works indicates that journey times were slower during the roadworks and faster afterwards, although it is also possible that the additional traffic negated that benefit.
  • We do know that it now takes longer to cross Gosforth High Street on foot because  pedestrian lights have been changed to prioritise traffic flow rather than crossing. The tongue-in-cheek Pedestrian Pain Index which estimates costs due to delays to walking journeys on a similar basis to the calculation for driving delays, is worth a read.
  • These results are consistent with a world-wide survey of cities published in “Cities and Automobile Dependence” (1989) by Kenworthy and Newman.  This concluded that the goal of “free-flowing” traffic (through such strategies as road widening) actually results in more fuel consumption and air pollution.  For a good summary see the Walkable Streets blog.
  • There are many similar studies that confirm that measures to improve flow will not reduce congestion either. This has been called the Fundamental Law of Road Congestion, which essentially states that any additional capacity for vehicles will quickly be filled negating any expected benefit.
  • One of the most effective ways of reducing traffic delays while also improving air quality is via congestion pricing.  In Stockholm, a where congestion pricing has received widespread public support, it has been estimated that without “congestion pricing”, children would have suffered 45 percent more asthma attacks. The video below by Jonas Eliasson gives a good overview of the approach taken in Stockholm and shows how public support for the approach grew significantly once  it had been implemented.

12 thoughts on “Roadworks, Air Quality and Disappearing Traffic

  1. Mrs Jan Oliver

    Has any one who writes this blog ever been to four lane ends between 8am and 9.30 and 2.30 -6pm?
    I live on Salters lane and have had to put up with motor bikes racing up and down every Saturday and Sunday, cars doing 90 miles an hour, 3 buses at the beginning of the road shut down, now down to 1 an hour. Final insult is no lighting when we walk over Hollywood bridge at all! and the end of this can’t wait to see if it has improved anything… I doubt it.

    Reply
    1. SPACE for Gosforth Post author

      Dear Mrs Oliver.

      Thank you for taking the time to read the article. I know the Four Lane Ends junction and have used it on foot, bike and by car. Most of us work during the times you mention though so it would help if you could clarify your comment.

      On your other points the speeding / dangerous driving is unacceptable and should be a matter for the Police, and we agree on the lighting. That needs fixing ASAP.

      Reply
  2. Malcolm Gara

    Have you looked at the current of traffic and air quality on Kenton Road between the Quick Fit garage, the Kenton Lane junction and down to the Jubilee junction? You will likely find a large increase here, the road is parallel to the High Street and it appears the displaced traffic is now using this route. The problem has simply been moved elsewhere.

    Reply
    1. SPACE for Gosforth Post author

      Hi Mr Gara,

      We can only use what data is available to us and there aren’t counters or air quality monitors on Kenton Road.

      Where there are monitors for traffic volume around Gosforth they generally show the same or reduced levels of traffic in the second half of 2017 compared to 2016, so if Kenton Road was higher that would be quite unusual. November is usually quite a busy month though so almost certainly just now there are quite high traffic levels.

      This is the link to the source of traffic data if you want a look. http://www2.gateshead.gov.uk/TADU/home.aspx

      Reply
  3. Henry Aarvold

    On the subject of “disappearing traffic” the article isn’t too clear as to what is specifically occurring. Obviously the traffic hasn’t disappeared, it’s either using different routes to avoid perceived bottlenecks (due to road works or junction “improvements”) or the drivers are resorting to alternative means of transport. Until the data collection and interpretation can indicate what is going on it’s probably unwise to assume anything. As other comments have indicated it’s probably more a case of “displaced” rather than “disappearing” traffic which certainly doesn’t solve any problem regarding pollution or congestion.

    The idea of punitively encouraging less car use with CAZs is a terrible idea. In exactly the same way was a raising duty on fuel is supposed to reduce car usage. It doesn’t unless there are convenient, reliable and affordable alternatives to traveling the same routes.

    What would change the behaviour of those people who use a car for (short) journeys for work, shopping, school or commuting? My personal opinion….

    Not much.

    The only big changes would be via a significant uptake in the use of hybrid/electric cars and bicycles.

    More people will buy electric as the technology continues to approve but perhaps the local authorities (and government) could do more to incentivise this?

    More people will cycle if they feel safer on the roads. That’s only going to happen if there is a huge commitment from local and national government to prioritising cycling as the primary means of moving the population of our cities and towns. The additional benefit to that is there is then a significant reduction in pollution, congestion, costs of road maintenance, deaths involving motor vehicles and people not in cars: just look at the studies from various cities around the world that have embraced cycling. It also improves the overall health of the population which can save huge amounts in health care over decades but that’s a debate for a different post I think.

    Reply
    1. SPACE for Gosforth Post author

      Dear Mr Aarvold,

      Certainly our preference would have been for better support to public transport, walking and cycling in advance of measures to reduce pollution but for whatever reason successive governments have not made that commitment, or at least not to the extent required.

      The Government’s position is that Clean Air Zones are the most effective way of reducing pollution. If you have time, the video about Stockholm is worth a watch and gives some data on the impact of charging and how people adjusted to that.

      We can’t say what happened to the traffic that was on Salters Lane other than that it is isn’t there any more and it hasn’t caused there to be more traffic on The Great North Road or Benton Lane. Even if some of it has chosen other routes, that means quite a lot of it has disappeared. Based on what has happened elsewhere this is exactly what we should expect. See E.g. http://rachelaldred.org/writing/thoughts/disappearing-traffic/ or https://nacto.org/wp-content/uploads/2015/04/disappearing_traffic_cairns.pdf

      Reply
  4. David

    Thanks for taking the time to do this blog. Can I ask where you get the traffic count data from for example Gosforth High Street and you could make this data public or point me in the direction of where the data can be obtained.

    Another point I wish to make about the “disappearing traffic”, During the roadworks at Salters Road and Church Road, the right turn was removed therefore cutting down the amount of traffic, it wasn’t really anything to do with it disappearing, people like me just took another route. I often have to visit the Ashburton Road area from Brunton Park and therefore since this right turn was banned I now take a right at Broadway West, then Wansbeck and Jubilee. It didn’t disappear, we just found alternative routes.

    The removal of the right hand turn will be indicative of this change not necessarily temporary roadworks and traffic lights, people just found other ways. Even to this day when coming up past South Gosforth Metro, I will take a left onto the Grove, drive to the top and take a right at the High Street, left onto Hawthorn and right onto Linden and come home via Wansbeck Road and this is simply because Church Road is choked many times a day because those traffic lights only allow three vehicles at a time to turn right. This is right in the heart of where the pollution monitors are and therefore the pollution is caused by city council schemes designed to alleviate it. Once again, the traffic doesn’t disappear, we find more easily flowing routes.

    If you consider that maybe 1 car turned right every minute or so in the past, then in a 12 hour period 7am to 7pm that’s a reduction of 720 traffic movements using alternative routes to avoid the banned right turn.

    If you could publish where you obtained the data or point me in the right direction I would be most grateful

    David

    Reply
  5. SPACE for Gosforth Post author

    Hi David,

    Thanks for the comment.

    All the data sources are listed in the notes section at the end of the blog. Traffic volumes are from the TADU website http://www2.gateshead.gov.uk/TADU/home.aspx

    There’s plenty of evidence that substantial amounts of traffic disappear when roads are shut. What the traffic data for Gosforth shows is just one example, This is a good summary: http://rachelaldred.org/writing/thoughts/disappearing-traffic/

    The GNR traffic count used in the blog in relation to disappearing traffic was from north of Hollywood Avenue so the right turn ban at Salters Road wouldn’t make any difference to this. I’m sure some vehicles did use other routes by the way. Even if half the 12000 vehicles had used another route that would still be a substantial reduction.

    There’s a counter on Jubilee Road by the way, which you will see on the TADU website. That shows a slight reduction from 2016 to 2017 as well.

    If you have any trouble with the TADU website, or find anything worth adding to the blog, please do let us know.

    http://rachelaldred.org/writing/thoughts/disappearing-traffic/

    Reply
    1. David

      Thanks for your reply

      Sorry if I seem to be missing something there, so if it’s north of Hollywood and I turned off much further north at Broadway West how does it not make any difference. I wouldn’t have driven past it and therefore in your eyes I would have disappeared and how can you correlate that traffic count with Salters Road when people can enter that section from further south at Regent Centre and Christon Road. Where exactly is the traffic counter.

      In relation to Jubilee Road, I said I travelled that way, others may have taken different routes for Salters Road, I am sure my one traffic movement, once a week didn’t make a difference. I think your disappearing traffic in Gosforth is unfounded. You can also get to Salters Road via Regent Road and many people, including me also use that route down back streets to avoid the stop start traffic. As for disappearing traffic, well I was stuck in it on Friday at 3pm and nothing seems to be disappearing. I think you’re just massaging the stats a little to suit a purpose. It’s my interpretation of it.

      David

      Reply
      1. SPACE for Gosforth Post author

        Hi David,

        The most important thing here is to understand what is going on so the right measures can be used to target air pollution. If you think you’ve spotted a flaw in the analysis please do say and we can investigate further. We do try to publish source data / evidence whenever we can specifically so people can check what we write, and if we’ve got something wrong we will correct it.

        In answer to your other points, the traffic counter we used for disappearing traffic (question 3) was north of Hollywood so the no right turn at Salters Road that you mentioned would make no difference to this. The traffic counter for air quality (question 1) was by The Grove.

        It’s not “our” disappearing traffic btw. The data is from the official council monitoring for all to see.

        Reply
  6. David

    Hello

    So I will ask my question again as you seem to be avoiding it – Where is the traffic counter, you said it’s north of Hollywood, but where north, that’s what I am asking. Is it near the speed camera, is it next to Asda. I did spot a flaw and I did point it out. How can you claim that the right turn at Salters Road makes no difference when the traffic count is north of Hollywood with many roads leading onto and off it before and after Salters Road. Please explain

    Reply
    1. SPACE for Gosforth Post author

      Hi David,

      The link I shared has all the monitors on it. Did you get that to work? The one north of Hollywood Avenue is pretty much right outside Gosforth Academy according to the map.

      Just reading back through your comment I think I owe you an apology as I misread it as suggesting people driving south went past salters road then turned right on one of the following roads. That journey would still be counted at the Gosforth Academy counter, as would someone turning right at the Regent Centre, but as you say if someone were to turn right at Broadway and go down Jubilee Road that would no longer be counted by Gosforth Academy so could appear as if it had disappeared.

      The only other nearby counter is at Jubilee Road which also shows a reduction from 2016 to 2017 so even if there is more traffic going Broadway West to Jubilee Road, some other traffic has moved / disappeared to compensate.

      Possibly someone might have travelled via Broadway West then onto Kenton Road but you would still expect the biggest effects to be on the nearest roads i.e. The GNR and Benton Lane.

      Reply

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