Few things are more frustrating for commuters than finding their journey into work unceremoniously halted by a red light. A new study suggests another reason, however, for commuters to try and avoid traffic lights – dangerously high levels of air pollutants.
Researchers from the University of Surrey in the UK have found that 25% of a driver’s total exposure to pollutant nanoparticles can come from passing through intersections controlled by traffic lights. This level of exposure occurs is the amount of time spent at traffic lights comprises as little as 2% of the total journey.
“Our time spent traveling in cars has remained fairly constant during the past decade despite the efforts to reduce it,” says 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.”
Nanoparticles emitted by the exhausts of cars have been associated with several health problems, includingasthma, cardiovascular disease and childhoodleukemia. People who live, work or travel near major roads have been linked with increased incidence and severity of these problems.
The US Environmental Protection Agency (EPA) state that previous research has indicated stopping very close to a vehicle at an intersection can increase the level of air pollution within the following vehicle.
“Air pollution was recently placed in the top 10 health risks faced by human beings globally, with the World Health Organization linking air pollution to 7 million premature deaths every year,” states Dr. Kumar.
Despite this, the study authors write that the contribution to commuter exposure to pollutant nanoparticles made by stopping at light-controlled intersections is largely unknown.
Red light spells danger
For the study, the authors monitored the levels of exposure to pollutant nanoparticles car drivers experienced at various stages of a journey.
Particle number concentrations (PNCs) were recorded during a busy 6 km round route that passed 10 signalized traffic intersections. Five different car ventilation settings were also tested, involving different levels of heating, fan use and degrees of window opening.
The study authors found that signalized traffic intersections had the highest levels of pollution, attributable to the frequent changes in driving conditions. Remaining in the same place for a period of time and revving up to move quickly when the lights changed resulted in high PNCs.
Peak PNC was 29 times higher at intersections with traffic lights compared with levels recorded during free-flowing traffic conditions.
The greatest reduction in in-cabin PNC related to outside PNC while in free-flowing traffic occurred with a fan drawing outside air into the cabin and the heating switched off. In delayed traffic, the greatest reduction was achieved with a fan on at 25% and heating on at 50%.
Cars also tended to sit close together when halted at signalized traffic intersections, increasing the likelihood of exposure to pollutant nanoparticles for the drivers.
How to limit your exposure
“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 Dr. Kumar. “The best ways to limit your exposure [are] to keep vehicle windows shut, fans off and try to increase the distance between you and the car in front where possible.”
Drivers are not the only people affected by the high levels of air pollution at signalized traffic intersections; pedestrians and cyclists also come into contact with them during the course of their journeys.
“Pedestrians regularly crossing such routes should consider whether there might be other paths less dependent on traffic light crossings,” Dr. Kumar recommends.
It is not just up to commuters to reduce their own exposures to pollutant nanoparticles. “Local transport agencies could also help by synchronizing traffic signals to reduce waiting time and consider alternative traffic management systems such as flyovers,” he suggests.