New Idling Research

New for 2021 TRL has produced research examining the emission profile of idling vehicles. By analysing Portable Emissions Measurement System (PeMS) data for various petrol and diesel vehicles TRL has established quantities of CO2 and NOx produced by idling.

The findings indicate that idling for a 30 second period produces nearly twice as much pollution as switching off then restarting the engine.

The findings of this research have been used in our Engine Off Every Stop campaign messages. Click here for the executive summary of this study.

The Challenge

Air pollution is a major environmental risk to health. Research by Imperial College London estimated that it contributed to around 4,100 deaths in London in 2019. 

Both short and long-term exposure to pollutants has been proven to cause and exacerbate illnesses ranging from eczema and itchy eyes to asthma, cancer and lung disease. 

What’s less well known is that air pollution is a particular concern for child health, as it can stunt lung growth and affect lung capacity. In fact, research conducted through a major study (the EXHALE project by King’s College London) found that the lung capacity of 8- and 9-year-olds in Tower Hamlets is 5% lower than the national average. 


Leaving engines running while stationary is simply an unnecessary source of air pollution.  It is also illegal.   Combating this is particularly important in locations where there are high numbers of idling vehicle engines, such as outside schools and hospitals, and by bus stops. 

Does idling really have an impact on air pollution?

The impact of idling on background levels of pollutants like NO2 is challenging to measure but we know that idling significantly increases localised pedestrian-level pollution, as well as increasing pollution levels within vehicles too. In a study by Kings College, air pollution levels were monitored during days when there were Idling Action events and were compared to non-action days.  Results suggested that pollution peaks on idling action event days were lower overall than on days where there were no events. 

It is important to consider that the pollution caused by idling is highly localised and concentrates around areas with high footfall. We have conducted air quality monitoring at some of our events. When stood next to an idling vehicle, we found PM levels were about 10 times higher than the average air pollution levels. 

How we encourage drivers to switch off

When engaging drivers we explain how air pollution affects the health of passers by as well as those inside the vehicle. We aim to educate and tackle misconceptions so that drivers will give up their idling habit for good. When approached in a friendly way, and when presented with facts about how idling and air pollution affect health, most drivers switch off their engines and many pledge never to idle again.  It’s a simple way everyone can help to instantly reduce vehicle emissions in London. 

Air quality in London

To find out what the air quality is like in your borough right now, please use this widget. It uses the Air Quality Index which is used to identify higher than anticipated pollution levels.