It seems that its not just in crime-ridden parts of town that stopping at red lights can be a health hazard. Vehicle pollution is causing thousands of premature deaths each year, and the damage has been found to be disproportionately done while stopped at traffic lights.
A team from the University of Surrey tested the pollution exposure of a group of U.K. car drivers on a typical 6-kilometer (3.7 mile) commute. In Atmospheric Environment, they report that exposure to nanoparticles from vehicle exhaust was 29 times higher when stopped at intersections with traffic lights than when moving in free-flowing traffic. Pollution was also raised in some intermediary locations, but waiting at red lights still accounted for 25% of the driver's dose, despite only being 2% of the commuting time for the sample.
The study was done with five different ventilation settings, including one with the windows fully open and another with various fan and heating combinations.
"Our time spent traveling in cars has remained fairly constant during the past decade despite the efforts to reduce it," said lead author Dr. Prashant Kumar. "With more cars than ever joining the roads, we are being exposed to increasing levels of air pollution as we undertake our daily commutes."
While the density of cars stopped at intersections is certainly a contributing factor, they found that revving up to accelerate away from red lights played a big part in vehicle emissions.
"It's not always possible to change your route to avoid these intersections, but drivers should be aware of the increased risks at busy lights," says Kumar. He notes that other commuters are even more exposed, despite not contributing to the problem, saying, "Pedestrians regularly crossing such routes should consider whether there might be other paths less dependent on traffic light crossings."
While there was a strong connection between the density of particulates inside the car and outside, this wasn't one-to-one. The biggest reduction, 88%, in internal particulate levels compared to the outside air was achieved with windows closed, fan on 25% and heating on 50%.
As depressing as this may be, Kumar did have some good news last year when he demonstrated that vegetation on busy roads can help reduce pollution by 36%. Looks like local authorities know where they need to be placing their trees.