Emission impacts resulting from vehicle idling

An operating vehicle emits a range of gases from its tailpipe into the atmosphere, one of which is carbon dioxide CO₂ – the principal greenhouse gas that contributes to climate change.

CO₂ is a colourless, odourless, gas that is a normal part of Earth’s atmosphere. However, when the amount of CO₂ in the atmosphere increases, more heat is trapped. This “enhanced greenhouse effect” causes Earth’s surface temperature to rise, which in turn is altering the world's climate.

CO₂ is also an unavoidable by-product of burning gasoline. Each litre of gasoline that is used produces about 2.3 kg of CO₂. Therefore, every time you start the engine, you're contributing to climate change.

Vehicles produce other emissions, such as volatile organic compounds (VOCs), carbon monoxide (CO) and oxides of nitrogen (NO_X), are criteria air contaminants (CACs) and these emissions are known to contribute towards air pollution and smog.

The following sections outline the impacts of your vehicle's GHG and CAC emissions.

Greenhouse gas emissions

For every litre of gasoline used, a vehicle produces about 2.3 kilograms² of CO₂, the principle GHG linked to climate change. With internal combustion engines, no technology exists for eliminating CO₂ emissions, an unavoidable by-product of burning fossil fuels. One simple and effective way to reduce the production of CO₂ emissions from light-duty vehicles is by choosing to eliminate unnecessary vehicle idling. This is an action that you – as a driver – can take.

Air quality emissions

Other vehicle emissions, such as volatile organic compounds (VOCs), carbon monoxide (CO) and oxides of nitrogen (NO_X) are criteria air contaminants (CACs) that contribute to air pollution and smog.

Advanced emission control technologies (e.g., catalytic converters, exhaust gas recirculation, engine monitoring sensors, computer controls and feedback systems) have dramatically reduced CACs from the tailpipes of new vehicles. In fact, today's vehicles produce 99 percent less CACs than vehicles built in the 1970's thanks to advances in engine and emission control technologies and improved fuel quality standards. However, CAC emission reductions from newer vehicles have been partially offset by the growing number of vehicles on the road and the greater distances we now travel.

Within the context of idling, while reducing unnecessary idling can save a significant amount of fuel and reduce GHG emissions, the effect on CAC emissions is dependent upon a variety of factors related to restarting the engine. A study³ completed in 2003 concluded that “there is little (CAC) impact in the choice of vehicle operation (idling or shut down) when the vehicle is stopped for durations between 10 seconds and 10 minutes”. What this means in terms of CAC emissions is that there is no substantial difference between turning the engine off and restarting it versus letting your vehicle idle, as both options produce some CAC emissions.

What are the benefits?

The 2003 study supports NRCan's position that “idling for over 10 seconds uses more fuel and produces more CO₂ emissions than restarting your engine.” This clearly confirms that there are direct benefits – in the form of fuel savings and reduced GHG emissions – that are obtained by turning the engine off instead of idling. As such, when considering all of the factors, the study showed it is better to turn the engine off rather than to let it idle unnecessarily.

What about diesel vehicles?

Diesel-powered vehicles are inherently more fuel-efficient than their gasoline-powered counterparts due to the higher energy (carbon) content of diesel fuel and combustion process efficiencies. Therefore a diesel vehicle will tend to travel further on a litre of fuel than a gasoline equivalent but will also produce more CO₂ emissions (2.7 kg CO₂/L⁴ – 15 percent more than gasoline).

When considering air quality emissions like CACs, it is also important to take into account the impact of diesel-powered vehicles. In general, diesels produce higher levels of particulates and NO_X than their gasoline counterparts and the best way to reduce these emissions is to turn the engine off. This is in addition to the reduction in fuel consumption and CO₂ emissions achieved by turning off the engine. Fewer than five percent of light-duty vehicles in Canada are diesel powered. On the other hand, heavy-duty diesel vehicles, such as school buses, delivery trucks and transit buses typically have larger diesel-powered engines and more limited emission controls as compared to light duty vehicles. These vehicles may idle for longer periods in communities and present their own specific CAC concerns and impacts on local air quality. More information on heavy-duty vehicles can be obtained at the Fleetsmart website.

So when should you turn your engine off?

Idling for over 10 seconds uses more fuel and produces more CO₂ compared to restarting your engine. However, as a more practical guideline, balancing factors such as fuel savings, overall emissions and potential component wear on the starter and battery, 60 seconds is the recommended interval. You will save money on fuel that should more than offset any potential increase in maintenance costs from any wear and tear on your starter or battery.

Idling initiatives around the world

Countries around the world are concerned with the impact of transportation on the environment and human health. Messages to reduce unnecessary idling are therefore a key component of many national climate change programs.

In Europe, the recommended guidelines for turning engines off are 10 seconds in Italy and France, 20 seconds in Austria, 40 seconds in Germany and 60 seconds in the Netherlands. In the United States, the Environmental Protection Agency's Smartway and Drive Wise programs both recommend turning the engine off if you're stopped for more than 30 seconds.

Avoiding unnecessary idling is a universal approach to reduce the environmental impact of vehicles. After all, idling gets you nowhere!

² Actual value: 2.289 kg CO₂/L – National Inventory Report 1990-2006, Table A12-7, April 2008

³ Review of the Incidence, Energy Use and Costs of Passenger Vehicle Idling. Gordon W. Taylor, P.Eng. Prepared for the Office of Energy Efficiency, Natural Resources Canada, 2003.

⁴ Actual value: 2.663 kg CO₂/L – National Inventory Report 1990-2006, Table A12-7, April 2008