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.


 

 
 
 
 

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