Mitsubishi introduces Concept GC-PHEV SUV to North America
Study: fully self-driving cars could result in fewer cars, but more miles driven per car

Study: stopping at red lights exposes drivers to high levels of particulates

UK commuters spend an average of about 1.5 hours a day at the wheel. Researchers at the University of Surrey have now found that where drivers spend just 2% of the journey time at traffic intersections managed by lights, this short duration contributes to about 25% of total exposure to nanoparticle emissions. Their study is published in the journal Atmospheric Environment.

PNCs [particle number concentrations] and change in driving speed showed an exponential–fit relationship during the delay events at TIs [traffic intersections]. Short–term exposure for ∼2% of total commuting time in car corresponded to ∼25% of total respiratory doses.

—Goel and Kumar

The team monitored drivers’ exposure to particle number concentrations (PNCs) at various points of a journey. Traffic intersections with signals were found to be high pollution hot-spots due to the frequent changes in driving conditions. With drivers decelerating and stopping at lights, then revving up to move quickly when lights go green, peak particle concentration was found to be 29 times higher than that during free flowing traffic conditions.

As well as concentration, researchers found that as cars tend to be close together at lights, the likelihood of exposure to vehicle emissions is also significantly increased.

Our time spent travelling in cars has increased by over 10% in the last ten years and with more cars than ever joining the roads, we are being exposed to increasing levels of air pollution as we undertake our daily commutes.

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. The best ways to limit your exposure is to keep vehicle windows shut, fans off and try to increase the distance between you and the car in front where possible. Pedestrians regularly crossing such routes should consider whether there might be other paths less dependent on traffic light crossings. Local transport agencies could also help by synchronizing traffic signals to reduce waiting time and consider alternative traffic management systems such as flyovers.

—lead author, Dr. Prashant Kumar


  • Anju Goel, Prashant Kumar (2015) “Characterisation of nanoparticle emissions and exposure at traffic intersections through fast–response mobile and sequential measurements” Atmospheric Environment doi: 10.1016/j.atmosenv.2015.02.002



"The only thing worse than stopping at red lights is not stopping at red lights."

As Oscar Wilde might have said.


+ what does this mean for cyclists and pedestrians ?


OK, Folks! The study is in. NO MORE RED LIGHTS! ZOOM ZOOM ZOOM!!!


mahoni - I think it means instant death. ZZOM ZOOM ZOOM!!!


Shared driverless BEVs with controlled decelerations and accelerations will eliminate the problem by 2025 or so.


@Harvey, That is an optimal solution.
Any kind of EV, even a full hybrid) if widely used, would do the trick.
They may or not reduce CO2 much, but they certainly reduce urban pollution.

Thomas Lankester

It is completely ridiculous that 17 years after stop-start entered mass production it is not being mandated for all new vehicles.

@mahonj - car drivers get it far worse as their air intakes are a lot closer to the exhaust of the vehicle in front. Cyclist are higher up and to the side, pedestrians even further away on the pavement. Still not good though.


Many larger 4 x 4 and light trucks direct their harmful exhaust to pedestrians on the nearby sidewalks.

Large trucks direct their exhaust upward and it falls on pedestrians a few feet further.

The comments to this entry are closed.