Has closing Hammersmith Bridge really improved London’s air quality?

Hammersmith Bridge. Image: Getty.

Hammersmith Bridge, opened in 1887, was indefinitely closed on the 10th of April 2019 as a result of “critical faults” found by safety sensors. It is currently closed to all motorists including buses but remains open to pedestrians and cyclists. The final plan has not yet been decided but it is estimated that the repair costs will be at least £40m.

Consequently, some argue that the bridge should be closed to motorists for good. However, Transport for London does not want to “lose” the bridge, so has pledged to spend £25m despite it being the responsibility of the council. Steve Cowan, Labour leader of Hammersmith & Fulham council, announced that the bridge “would reopen to motorised traffic within three years”.

Hammersmith has persistently had air quality problems and has the eighth highest percentage of early deaths attributable to air pollution in London, according to a report by King’s College London. It has been a designated air quality management area since 2010. Understandably, residents were therefore concerned about the increased congestion leading to higher levels of pollution.

We therefore decided to investigate if we could find any effect on air quality due to the closure of the bridge. For our investigation, we primarily used data from three continuous Air Quality Monitoring Stations in the Borough of Hammersmith and Fulham and Wandsworth. Their locations are shown below in red.

Pollution levels are measured hourly. We used the NO2 results, as this is both one of the main pollutants released by cars and is almost entirely released by cars.

Looking first at Hammersmith Town Centre, there is a general decline in the level of pollutants in the town centre. However, this decline began before the closure of the bridge and in fact was sharper before it.

Does this mean that there is cause for concern? Is the closure perhaps retarding air quality improvements? Well, the data demonstrates that the level of pollutants is lower, peaks less frequently. and when it does peak it is generally lower than before the closure. The standard deviation before the closure was 75.1, whilst after it is 54.8. This significant change suggests that the closure of the bridge has had an effect on pollutants in Hammersmith town centre.

To a lesser extent, the same trends can be seen in Shepherd’s Bush. There is a slight overall decline. However, as in Hammersmith, the decline started before the closure and has since become more gradual. The maximum levels per day also decreased and anomalously high results were also less frequent.

However, the change in standard deviation was less significant in Shepherd’s Bush (30.2 before the closure and 21.2 after) most likely due to Shepherd’s Bush being significantly further from the bridge.

On the other side of the Bridge in Putney, the same trends can be identified although they too are less significant than the data from Hammersmith Town Centre probably owing to the further distance. However, as the level of pollution has not increased as a result of additional congestion caused by the closure there is no apparent environmental damage. In fact, if the increased congestion or overlong diversions have caused residents to use other methods of transport this could explain the lower maximum results, indicating that the closure has actually had a slight beneficial impact on air quality in Hammersmith.

It seems that, at least whilst the bridge is closed, some people are choosing more environmentally friendly modes of transports knowingly or otherwise. Will this change people’s habits for good? It’s hard to say. But maybe this is a chance to improve public transport and the liveability of surrounding streets so that congestion can be reduced for good and the good people of Hammersmith can breathe cleaner air.

Eletta Rainsford is working with Create Streets before completing her studies in maths and statistics. This is her first published article.


 

 
 
 
 

Tackling toxic air in our cities is also a matter of social justice

Oh, lovely. Image: Getty.

Clean Air Zones are often dismissed by critics as socially unfair. The thinking goes that charging older and more polluting private cars will disproportionately impact lower income households who cannot afford expensive cleaner alternatives such as electric vehicles.

But this argument doesn’t consider who is most affected by polluted air. When comparing the latest deprivation data to nitrogen dioxide background concentration data, the relationship is clear: the most polluted areas are also disproportionately poorer.

In UK cities, 16 per cent of people living in the most polluted areas also live in one of the top 10 per cent most deprived neighbourhoods, against 2 per cent who live in the least deprived areas.

The graph below shows the average background concentration of NO2 compared against neighbourhoods ranked by deprivation. For all English cities in aggregate, pollution levels rise as neighbourhoods become more deprived (although interestingly this pattern doesn’t hold for more rural areas).

Average NO2 concentration and deprivation levels. Source: IMD, MHCLG (2019); background mapping for local authorities, Defra (2019).

The graph also shows the cities in which the gap in pollution concentration between the most and the least deprived areas is the highest, which includes some of the UK’s largest urban areas.  In Sheffield, Leeds and Birmingham, there is a respective 46, 42 and 33 per cent difference in NO2 concentration between the poorest and the wealthiest areas – almost double the national urban average gap, at around 26 per cent.

One possible explanation for these inequalities in exposure to toxic air is that low-income people are more likely to live near busy roads. Our data on roadside pollution suggests that, in London, 50 per cent of roads located in the most deprived areas are above legal limits, against 4 per cent in the least deprived. In a number of large cities (Birmingham, Manchester, Sheffield), none of the roads located in the least deprived areas are estimated to be breaching legal limits.

This has a knock-on impact on health. Poor quality air is known to cause health issues such as cardiovascular disease, lung cancer and asthma. Given the particularly poor quality of air in deprived areas, this is likely to contribute to the gap in health and life expectancy inequalities as well as economic ones between neighbourhoods.


The financial impact of policies such as clean air zones on poorer people is a valid concern. But it is not a justifiable reason for inaction. Mitigating policies such as scrappage schemes, which have been put in place in London, can deal with the former concern while still targeting an issue that disproportionately affects the poor.

As the Centre for Cities’ Cities Outlook report showed, people are dying across the country as a result of the air that they breathe. Clean air zones are one of a number of policies that cities can use to help reduce this, with benefits for their poorer residents in particular.

Valentine Quinio is a researcher at the Centre for Cities, on whose blog this post first appeared.