Transportation is consistently identified as one of the largest contributors to air pollution in Canadian cities. In the Toronto region, vehicle emissions from personal cars, trucks, and commercial vehicles account for a substantial share of the nitrogen oxides, fine particulate matter, and greenhouse gases that affect air quality and public health. Improving public transit — both its capacity and its reach — is one of the most direct ways to address this problem at scale.
The logic is straightforward: a single subway train or articulated bus can carry hundreds of passengers, removing a corresponding number of vehicles from the road. Each vehicle removed represents a reduction in tailpipe emissions — emissions that would otherwise disperse at street level, where pedestrians, cyclists, and children are most directly exposed. At scale, high-ridership transit systems produce substantially lower per-passenger emissions than private vehicles, even accounting for the energy required to run the transit system itself.
The Pollution Picture in Toronto
Toronto sits in a geographic basin that can trap air pollutants under certain weather conditions, making local emission sources especially consequential for air quality. The city has made measurable progress on air quality over several decades, partly through vehicle emission standards and the phasing out of coal power in Ontario. But transportation-related emissions remain a significant remaining source of urban air pollution.
Fine particulate matter — particles small enough to penetrate deep into the lungs — is a particular health concern. It is generated by combustion engines, as well as by brake and tire wear, meaning that even a shift to electric vehicles does not entirely eliminate the particulate contribution of road traffic. Reducing the number of vehicles in operation, through higher transit ridership, addresses both emission types simultaneously.
The Role of Transit Quality
The relationship between transit quality and ridership is well-established: when transit is fast, frequent, reliable, and comfortable, more people use it. When it is slow, crowded, and unreliable, people who have alternatives will choose them. This means that improving air quality through transit is not simply a matter of having transit available — it requires investing in transit that people actually choose to take.
Frequency is arguably the most important factor. A bus that runs every 20 minutes requires trip planning and carries a real penalty for missing it. A bus that runs every 5 minutes functions more like a continuous service — you show up and go. The TTC's surface routes, which carry a large proportion of transit trips in Toronto, vary significantly in frequency across the network, and lower-frequency routes in outer areas of the city tend to serve lower-income populations who depend on transit most.
Transit Electrification
The environmental benefit of transit is multiplied when transit vehicles themselves run on clean energy. The TTC has been working toward electrification of its bus fleet over the coming decade. Electric buses produce no tailpipe emissions and, on a grid powered substantially by low-carbon sources — as Ontario's electricity grid increasingly is — result in significantly lower lifecycle emissions than diesel equivalents. The combination of higher ridership and cleaner vehicles represents the strongest possible scenario for transit's role in reducing urban air pollution.
Beyond the Numbers
Air quality affects health outcomes that are distributed unequally across the city. Neighbourhoods close to major highways and arterial roads experience higher concentrations of vehicle-related pollutants than quieter residential areas. These same neighbourhoods often have limited access to green space, and their residents may be less able to choose where they live. Improving transit quality in these areas — providing fast, frequent service that allows residents to travel without adding to the pollution they are already disproportionately exposed to — is both an environmental and an equity issue.
The City of Toronto and the Province of Ontario have committed to various transit expansion projects. Whether those projects ultimately deliver on their air quality potential will depend on how well they integrate with the existing network, how frequently the new services run, and how aggressively the fleet is electrified. Public engagement in holding those commitments to account is part of what campaigns like Your32 are designed to support.
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