How would the proposals improve air quality?

Air pollution, caused by emissions of toxic gases and aerosols into the atmosphere, is a public health crisis. In 2020 alone, 121 deaths in Greater Cambridge were attributable to air pollution. In terms of particulate emissions, the WHO has stated that there is no safe level of exposure at which harmful effects do not occur.

Air pollution is clearly linked to serious health conditions including asthma and other respiratory conditions, heart and lung disease, dementia, miscarriage, teenage psychotic episodes, and reduced cognitive ability. If children grow up in polluted areas and are exposed to air pollution over a long period of time, it can affect how their lungs develop. Children in polluted area are much more likely to develop asthma.

The Greater Cambridge Partnership (GCP) estimates that with the proposed Sustainable Travel Zone fully operational, levels of nitrogen dioxide, a major pollutant, will decrease at nearly 90% of locations it studied. Levels of particulate emissions will also decrease as traffic levels fall.

Emissions from diesel buses, however, make a significant contribution to air pollution in the historic city centre and around the Drummer Street bus station. The Cambridgeshire Sustainable Travel Alliance call on the Cambridgeshire and Peterborough Combined Authority to accelerate the adoption of electric buses to make sure air quality for some residents is not negatively impacted by the current proposals.

Cars queuing at the Chesterton Road / Elizabeth Way roundabout in Cambridge

Nitrogen dioxide (NO2)

The gaseous pollutant NO2 can have serious health effects, leading to new diagnoses of asthma and accentuating asthma symptoms in those who already suffer. Levels of nitrogen dioxide (NO2) have been found to be above legal limits set for the protection of human health within Cambridge city.

The main source of NO2 emissions in Cambridge is from road traffic, in particular diesel vehicles. Concentrations are particularly high on congested roads and roads with high traffic flow. Cambridge City Council designated an Air Quality Management Area (AQMA) inside the ring road in 2004 because of the high average levels of NO2 in the centre of the city.

The Sustainable Travel Zone proposals would reduce the traffic in Cambridge by an estimated 50%, which would immediately reduce congestion and improve air quality. As stated above, the GCP estimates that with the Sustainable Travel Zone fully operational, levels of nitrogen dioxide will decrease at nearly 90% of locations it studied.

Work is also underway to reduce nitrogen concentrations in the city from other angles. Diesel buses currently account for a high proportion of nitrogen dioxide emissions from Cambridge’s road traffic inside the inner ring road. The Cambridgeshire and Peterborough Combined Authority has pledged to have an entirely electric bus network in the area by 2030, ie two or three years after the Sustainable Travel would be fully operational. The first two electric buses are already in operation and 30 more zero emission buses will be arriving soon.

The GCP is proposing orbital bus routes (ones that go around the city), as well as routes in and out of the centre, as part of its network transformation. Spreading bus stops and bus routes out more evenly throughout the city will help to improve air quality.

Airborne particulate matter (PM)

Airborne particulate matter (PM) is a generic term for the tiny particles (often less than a tenth of the width of a human hair) released into the atmosphere from engine exhausts, tyres and brake wear and road abrasion, and from the re-suspension of particles already on road surfaces as vehicles pass over them.

The most serious health effects come from particles known as PM2.5, which have a diameter of 2.5 microns and smaller. These particles can penetrate into the lung and cause damage there. Even smaller particles can even cross into the bloodstream and transfer from there to other organs, for example the brain, potentially affecting development. Particles have been found to pass from mothers to the lungs, livers and brains of unborn babies, potentially causing lifelong health effects.

The World Health Organisation (WHO) has made it clear that airbone particulate matter is an extremely serious health concern:

“There is no evidence of a safe level of exposure or a threshold below which no adverse health effects occur”.


While electric vehicles emit less airborne particulate matter than conventional vehicles due to regenerative braking, the best way to reduce exposure to airborne particulate matter (PM) is to bring down traffic levels. The 50% reduction in traffic levels predicted to result from the Sustainable Travel Zone would significantly reduce particulate emissions from motor vehicles.

Pollution levels inside motor vehicles

Perhaps contrary to what might be expected, some of the worst levels of air pollution can actually be found inside motor vehicles. Various studies have shown that drivers and passengers are exposed to more pollution inside their vehicles than those walking and cycling the same routes. The plans to improve walking and cycling links as part of the package of measures proposed by the GCP would enable more people to reduce their exposure to air pollution by switching to walking and cycling for their daily journeys.

Asthma and Lung UK supports the Cambridgeshire Sustainable Travel Alliance

Asthma + Lung UK logo

National Charity Asthma and Lung UK supports aims of the Cambridgeshire Sustainable Travel Alliance. Further information about the charity can be found on our members page.

Tim Dexter, Campaigns Manager at Asthma + Lung UK says:

“Air pollution from road transport has devastating health impacts on people living with lung conditions. Residents of Cambridgeshire deserve to breathe clean air. Improvements to public transport, walking and cycling infrastructure will help to reduce the levels of toxic air pollution that are damaging to people’s health.”

In an article for the Cambridge Independent, he states further:

“We know from experience that charging zones work. Cities like Birmingham, Bath and London have seen a rapid reduction in pollution levels after introducing their zones over the past few years.”

Cambridge Independent, 23rd November 2022