Quantifying Impact of Idling on Air Quality

Access the working paper here.

In a number of cities, vehicular congestion on roads is a growing problem. Now a range of innovative ways exist to know, in advance, where the congestion is, what roads to avoid at certain times, and what alternatives exist. While the time and resources (fuel) are wasted sitting in congestion, an invisible problem hurting the human health, the most, is the extra pollution due to idling.

This piece is an effort to quantify these emissions due to idling on road and illustrate a methodology.

Please note that the calculations presented are subjected to authors assumptions and approximations, and the reader should pay attention to the methodology and use the parameters presented with discretion.

Click on the tables to enlarge view.

In a previous post, a set of average emission factors (gm/km) for various vehicular categories were presented and summarized below.



Lets assume an average mileage (km/lit), as shown below, for the mix of vehicles presented in the above table.



Now, gm/km * km/lit = gm/lit
This would result in the emission per liter of fuel (gm/lit), for the mileage assumed for the vehicular fleet and the results are summarized below.



On an average, idling is assumed to consume about 1 liter per hour for cars and about 2 liter a medium size heavy duty vehicle. An average amount of fuel required for idling (lit/hr) is presented in the table below.



On an average, for an urban vehicular fleet, the following VKT is assumed (km/day). For more on how to survey the on road fleet for VKT's, see the SIM-series.



How much is the idling in real time?
This is THE question and the answer will guide the rest of the calculations and any conclusions will depend on this assumption. My assumed idling minutes (mins/day) are below.



In the above table, a higher value is assumed for the buses because of their multiple trips and the amount of time they spend on the road, compared to the 2Ws or Cars, which depend on the usage type (work or personal). These assumptions also depend on the local travel conditions.

Now, total emissions due to driving (gm/day/vehicles) = gm/km * km/day, which results in the following table, with units of gm of pollutant emitted per day each category of vehicle, for that many km's of travel per day.



Now, total emissions due to idling (gm/day/vehicle) = gm/lit * lit/hr * mins of idling/60, which results in the following table with units of gm of pollutant emitted per day for each category of vehicles, for the assumed amount of idling per day.



An interesting analysis lies in the table below, which presents the percent of emissions due to idling for the assumed scenario.



The percent emissions due to idling per day and per vehicle, for 2Ws and Cars, is proportionally high due to their less VKT's compared to HDVs or Buses.

At an individual level, the 2Ws and Cars look like they emit less, but when multiplied with the number of vehicles on road, their portion of total emissions is high and their impact on local air pollution (and human health) is very evident, along with the trucks and buses.

Note that these calculations will be different, with any of the numbers changed.

Having said that, it is important to note that idling is increasingly contributing more to the air pollution than before and lot of can be avoided by either using the vehicles less at the personal end and a better traffic management at the policy end.

See some analysis on impact of idling by Dr. Suvrat Kher for Pune, India.

Gulf News, March 3rd, 2009 - UAE loses Dh10.5b to traffic congestion.

Please turn off your engine, if you are going to idle for more than 30 sec.