STM - Society in motion
How do we calculate that Travelling by public transit emits 20 times less CO2 than travelling by car? March 14, 2011
The calculation used to arrive at this result is based on several factors.
1. The Origin-Destination study conducted in 2008 enabled us to determine that the average distance travelled during a trip on the STM network is 8.3 km, of which 5.3 km occurs on the métro. We also learned that the average number of passengers in a car is 1.3.
2. Our calculations are based on a rush hour scenario with an average of 65 passengers per bus. We can then calculate the CO2 emissions from the bus divided by 65 to obtain the emissions per passenger-km. As for the métro segment, we know that the métro emits no CO2, as it is 100% electric.
3. We then compare the emissions for the same 8.3-km trip carried out by a car with 1.3 passengers.
By taking the bus instead of your car, you are cutting your polluting emissions by more than half. May 2, 2010
When comparing the emissions of a car ride with those of a bus ride, several data are taken into account:
- the average emissions of a car per travelled kilometre, as published by Transport Canada;
- the average number of persons per car according to the Origin-Destination survey (1.25 person);
- the emissions by all STM buses for all hours of transit service;
- bus ridership and the average length of a bus trip (km-passenger).
Polluting emissions include :
- carbon monoxide (CO)
- nitrogen oxides (NOx)
- sulphur dioxide (SO2)
- volatile organic compounds (VOC)
- total suspended particulates (TSP)
Polluting emissions are not produced in the same proportion for buses and cars.
Our calculations show that, when combining all hours of STM service, they are 2 to 10 times lesser for a bus than for a car, depending on the pollutant.
During rush hour, emissions are 7 to 44 times lesser for a bus than for a car. This is based on an average of 65 passengers per bus, which is equal to 50 cars (65 persons divided by 1.25).
