Close the windows in traffic queues, say experts.
The World Health Organization (WHO) describe outdoor air pollution as a "major environmental risk to health," linking it to 3.7 million premature deaths worldwide in 2012.
In 2013, the WHO classified outdoor air pollution in cities as being as carcinogenic to humans as smoking was in February 1985.
In the United States, exposure to particulate matter in the air is the eighth leading cause of death each year. In London in the United Kingdom, deaths related to air pollution are estimated to be 10 times higher than fatalities caused by road traffic accidents.
Research led by Dr. Prashant Kumar, from the University of Surrey, U.K., has shown that 25 percent of exposure to harmful particles when driving occurs in the 2 percent of the journey time that drivers spend passing through intersections with traffic lights.
Pollution at intersections is 29 times higher than on the open road
At intersections, vehicles slow down, stop, rev up to move when lights turn green, and they are closer together.
- On the U.S. air quality index, the worst scoring places on 26 August, 2016 were in New Jersey and California
- These locations scored between 101-150 on the index, considered "unhealthy for sensitive groups"
- "Good" scores are from 0-51, and 151 or over is "unhealthy."
This leads to levels of peak particle concentration at a signalized intersection that are 29 times higher than those found in free-flowing traffic. In addition, the cars move slowly, so that drivers are exposed for longer. As the output is ongoing, the pollution does not disperse but lingers and accumulates.
As a result, cars waiting in traffic jams or at red lights contain up to 40 percent more pollution than those that are moving.
In a new study, Dr. Prashant and his team have been looking for a solution.
The scientists took measurements of particulate matter in a moving car under five different ventilation settings. The car traveled 6 kilometers and passed through 10 different traffic lights.
They took measurements at 3-way and 4-way intersections managed by traffic lights.
The authors wanted to see how the different ventilation settings would affect particulate matter inside the car. They also looked at how levels of pollution within the car compared with those experienced by pedestrians crossing roads at the same traffic lights.
Results showed that the ventilation system of the car was efficient at removing coarse particles from the air, but as the concentration of coarse particles fell, the number of fine particles increased. The highest levels of pollution within the car tended to occur when the windows were closed at the traffic lights and the fan was on.
Pedestrians at intersections were also exposed to additional pollution, but the level of particulate matter to which motorists were exposed was up to seven times that experienced by pedestrians.
Close the windows and shut off the fan in traffic jams
To reduce the amount of pollution exposure while waiting in traffic jams and at traffic lights, the authors suggest that, weather permitting, motorists should close car windows and switch off the fan. This, they say, can reduce the chance of breathing in hazardous levels of air pollution by 76 percent.
They also recommend setting the fan so that the air circulates internally. Recirculating the air prevents pollution from entering from outside.
"Where possible and with weather conditions allowing, it is one of the best ways to limit your exposure by keeping windows shut, fans turned off and to try and increase the distance between you and the car in front while in traffic jams or stationary at traffic lights.
If the fan or heater needs to be on, the best setting would be to have the air re-circulating within the car without drawing in air from outdoors. Of course improving the efficiency of filtering systems of vehicles in future could further benefit to curtail the on-road exposure in such situations."
Dr. Prashant Kumar
In 2015, Dr. Prashant and his team called on drivers to be aware of the hazards of pollution at intersections, and they suggested that keeping a distance from the car in front could help to reduce the risk.
The researchers urged pedestrians to find walking routes that did not include signalized traffic intersections. They also noted that local transport authorities could help by synchronizing traffic signals, as this can reduce waiting time. Alternative traffic management systems such as flyovers could also help to alleviate the problem, they say.