Public Health England talks about steps that can be taken to reduce air pollution.
One of the recommendations is to stop the vehicle from moving in places such as schools and hospitals.
There was relatively little research on how it is a common phenomenon that goes beyond schools outside schools.
However, it is clear that when considering the impact, the type of vehicle involved is key, with significantly lower emissions generally coming from newer vehicles.
Many modern cars and buses have a stop-start system that automatically switches off the engine when the vehicle stops, although they may be disabled.
The project commissioned by the London Mayor's office in 2016 measured pollution changes after a series of "days of action", with teams of volunteers patrolling the streets in four areas in London, urging drivers to turn off their engines.
They found that the level of black carbon-pollutant associated with the exhaust gases of the car, which was associated with lung and heart disease – was 36% lower after these "days of action" to a primary school in Wandsworth.
But the results were not so convincing in all areas – in the city of London there was an increase of 33% on the first test day and a 22% decrease in the latter.
The researchers say the Wandsworth location is particularly suitable for the study, while in the central locations, rails and trucks are spreading along the street, rather than being concentrated in one place. This makes it difficult to measure a strong signal.
The report says that the school gaps empty "is a problem in the capital and it was pleasant to see the largest drop in concentrations" outside the school.
A piece of research in the United States, published in 2013, looked at air quality in four schools before and after campaigns to stop vehicles in a vacant holiday.
It found that there was a significant reduction in air pollution in multi-bus schools – those with fewer buses did not noticeably reduce the concentration of air pollutants.
Local authorities in the United Kingdom already have the authority to issue fixed-penalty notices to drivers in parked vehicles who refuse to turn off their engines when asked.
The Camouston Emissions Consultant considered when it is worth switching the engine to reduce emissions.
It found that for emissions of nitrogen oxide from a diesel car that meets the Euro 5 requirements (which is largely any diesel car made before the end of 2015), it is worthwhile to turn off the engine if you expect to be steady at least 30 seconds.
For diesel cars from Euro 6 (those produced after 2015) it's worth disengaging if you do not move for three seconds.
The company also told the BBC that most shows come from a very cold start at the start of the day and acceleration. Rapid bumps cause particularly high emissions due to this.
The body that produces national health guidelines, the National Institute of Health and Excellence, can not find strong evidence linking changes in the style of driving with changes in ambient air pollution. But it also agreed that encouraging people to change their driving style is "unlikely to have any adverse effects".
Transport for London says it tells its bus drivers to turn off their engines on bus stands and when regulating the service, and adds that it will ensure that all buses in London have by-emission engines by 2037.
FirstGroup, which works with local bus services across the UK, says it encourages drivers to switch off their engines "wherever possible" and that the engines of their new vehicles will automatically be cut off if they are idle for a certain period of time.
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