Effect of Wightman Road Filtering on Haringey Air Quality

Background

Haringey has long been declared an Air Quality Management Area (AQMA) because of pollutants such as Nitrogen Dioxide (NO2). Councils with AQMAs are required to monitor pollution levels, and produce action plans to tackle the causes. The following table uses Haringey Council’s website data (see Appendix), and shows the percentage change in NO2 levels at various monitoring sites between 2015 and 2016 (some recently closed or newly opened sites are not listed since comparison between years is not possible).


Analysis

Figures in green indicate decreased pollution, figures in red indicate an increase, compared to the previous year. Although N02 dispersion is a complex phenomenon and the monitoring equipment itself is not 100% reliable, the year-on-year monthly figures provide evidence that filtering Wightman Road, after the initial disruption, actually had a widespread overall positive effect on pollution:
  • The Wightman Road closures initially caused disruption and traffic congestion in April so one would expect higher pollution, and this is evidenced e.g. by the 35% increase in April 2016 compared to April 2015 at site HR27 (Green Lanes). The disruption can be attributed to factors such as initial signage issues which the Council later corrected, or traffic light phases no longer matching the flow at key junctions. Also as above, most traffic is through-traffic, and most drivers are not local, so would rely entirely on signage to be aware of the new road layout (the Council obviously did consult and leaflet the local community about the changes, but most through-traffic would not have been aware of that). 
  • Congestion improved slowly but significantly through May and June, so one would expect the increased pollution also to subside, again this is evidenced by the fact that the June column in the above table is highlighted mostly in yellow rather than the red seen in previous months. The improvement took many weeks, again partly because so much traffic is non-local, but also because of other major changes in surrounding transport network at this time - for example, the extensive roadworks at Finsbury Park & Stroud Green Road affected bus and other journeys along Seven Sisters Road, and the closure of the GOBLIN (Gospel Oak – Barking line) would have put significant additional pressure on both public and private transport using Seven Sisters Road and other east-west routes. 
  • The SDG consultants calculated an 8% “evaporation” of traffic between March and June, but the pollution evidence in August, when most sites are highlighted green to indicate reduced pollution compared to 2015, suggests that the “evaporation” process was still continuing during the summer. There may be other causes of the reduced pollution but the fact that by now it is now much more attractive to make journeys by cycling or walking or public transport, is highly likely to be one of them. 
  • The bridge re-opened and the Wightman Road barriers were lifted in early September however the reduced pollution relative to 2015 actually continues into October/November. Again, as so much traffic is non-local and took several months to switch to alternative routes or transport modes, it is not surprising to see it take a few more months before everyone realises the rat-run is now open again. 
  • However by December it seems the traffic is just as bad if not worse than was at the beginning of the year, and pollution actually now worse relative to December 2015.

Conclusions

As stated above NO2 pollution is a complex phenomenon and we have to be cautious trying to draw definitive conclusions, however there does seem to be strong evidence in favour of the assertion that filtering Wightman Road, after an initial disruptive period of adjustment to surrounding traffic flows, within a few months actually had an overall beneficial effect on pollution levels across a much wider area; and no evidence at all for the idea that the many other benefits of filtering Wightman were only bought at the expense of making pollution worse elsewhere.
In fact if filtering Wightman had originally been a Council initiative as part of its Air Quality Management Plan, we think they would now be shouting the results from the rooftops!
We are therefore urging the Council to continue developing the Wightman Filtering package of options developed by the Transport Study, rather than its currently preferred solution of “Minor Improvements”, which is not expected to have a significant effect on the traffic and pollution issues which prompted the Transport Study in the first place.

Appendix: Haringey pollution data

The following tables show the actual pollution levels at each of Haringey’s monitoring locations. The EU and UK target levels for NO2 are 40mg/m3, so levels below this are highlighted in green and levels above in gradually darker shades of red:


2015 figures taken from p27 of Haringey Council website here, 2016 figures taken from p26 of Haringey Council website here.