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.
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).