Walk up Yonge Street from say King St. to Eglinton Ave. It is a hike, 6.7 kilometers (4 miles), almost all uphill. Then, drive a car, say a Ford Fusion, which weighs upwards of 1.5 metric tons. That would involve burning a bit more than half a liter of gasoline (this is just a rough estimate; I used NRCan’s fuel consumption ratings for 2011), which would put 1.6 kilograms of carbon dioxide (CO2), the main manmade greenhouse gas, into the air (again, using an NRCan estimate that says one liter of burned gasoline will produce 2.4 kilograms of CO2).
Then, take a subway. The Toronto subway is electric powered. Electricity is supplied by Toronto Hydro, which says it supplied 24.7 billion kilowatt-hours to the city in 2010. Nearly a quarter of that—over 5.6 billion kWh—went to the Toronto Transit Commission (TTC); the TTC says that 77 percent of those 5.6 billion kWh was for traction power, i.e. the electricity used to move subways and streetcars. All of which is to say, the TTC in 2010 used nearly 4.4 billion kWh to move hundreds of thousands of passengers on subways and streetcars.
A TTC subway ride from King to Eglinton on the Yonge Street line would take 15 minutes to get from the King subway station to Eglinton (according to the TTC trip planner). An average TTC subway train is 6 cars. From a study of electricity consumption of electric trains which estimated that a 16-car uphill train trip in Taiwan takes 105 minutes and uses 2,021 kilowatt-hours, I estimate that a 15-minute six-car TTC subway train travelling uphill from King to Eglinton would use just over 108 kWh.
At 12:00 p.m. today, the emission intensity of Ontario electric power generation was 184.8 grams of CO2 per kilowatt-hour. So the 108 kWh used in that 15-minute subway trip from King to Eglinton on the Yonge line would have come with just over 20,000 grams, or 20 kilograms of CO2.
Here is the kicker. At capacity, that subway train would be carrying around 1,000 passengers. If all those passengers were going from King up to Eglinton, each one would be responsible, through the subway’s electricity use, for around 20 grams of CO2.
Let’s compare that to the Ford Fusion mentioned above. The Fusion, driving up Yonge Street from King to Eglinton, would put 1.6 kilograms of CO2 into the air. That is eighty times as much CO2 as the equivalent ride in a full subway. Fill the car with four adults and do the same trip, and each of those adults is responsible for 20 times as much CO2 as each subway rider doing the same trip.
Do the subway trip at say seven a.m. instead of 12:00 p.m., and the subway trip becomes even cleaner: the emission intensity of Ontario electricity is around 100 grams CO2 per kWh at that hour.
By contrast, the car trip never gets cleaner. Gasoline is gasoline, and every liter emits 2.4 kilograms of CO2 when it is burned.
Toronto subway rider: your ride is very, very clean.