The Board acted in part on a report from Dr. David McKeown, Toronto’s medical officer of health, which stated:
For every litre of gasoline used, about 2.4 kg of CO2 are produced; for every litre of diesel fuel consumed, about 2.7 kg of CO2 are produced. The Clean Air Partnership estimated that idling in the GTA [Greater Toronto Area] wastes 90 million litres of fuel each year, suggesting that over 215 million tonnes of CO2 are emitted in the GTA each year as a result of idling. Assuming that vehicle ownership is distributed evenly across the GTA, Toronto’s contribution could be 105 million tonnes of CO2 each year as a result of idling.The cars of yesteryear needed warming up because they used heavier motor oil which needed warming to fully lubricate the engine. Modern cars with computer controls need at most 10 seconds before they are ready to drive. Shutting off an engine if it would idle more than 30 seconds will save gas, although there are more effective eco-friendly driving steps.
Added McKeown, “I understand why people want to get into a warm car, but the price we pay for that is our health.”
The shorter limit was previously adopted by the Ontario city of Burlington, but is "widely ignored" and sporadically enforced.