A report released by the Health Effects Institute (HEI), an independent US-based non-profit research organisation, found that air pollution accounted for 8.1 million deaths globally in 2021. Beyond these deaths, many more millions of people are living with chronic diseases, which are typically managed through hospitals and public health programs. These health systems face increasing pressure, along with economic and societal impacts. Increasingly, air pollution is one of the biggest threats to our well-being today. One of the major contributors to increasing air pollution is private transportation. For example, the transport sector contributes to a third of India's particulate matter (PM) pollution and 20-35 per cent of PM 2.5 pollution in urban India. Due to the convenience, private automobile ownership has increased tremendously, leading to more pollutants like nitrogen oxides and particulate matter entering the atmosphere. This is why governments everywhere are forced to look into sustainable alternatives in order to improve air quality, like public transportation, green spaces, zoning regulations etc.
One of the common ways is increasing people’s reliance on public transport, which is done by subsidizing public transportation fare. By using public transportation, people can contribute to reducing the number of private vehicles on the road, promoting cleaner energy sources, using efficient routes and planning, encouraging walking and cycling, and supporting government initiatives. However, whether or not this affects air pollution remains an open question. A study that conducted a comprehensive review of the literature on the effects of public transport investment on urban transportation dynamics, focusing on traffic congestion and air quality, found that despite the widespread belief in public transit investment, the empirical evidence on its reducing congestion and air pollution remains mixed and depends on the local conditions. Additionally, the magnitude of these benefits is uncertain and varies significantly across different urban areas.
It is important to understand how the public transport subsidies adopted in different countries have affected their air quality, which is gaining popularity among governments in Europe. In March 2020, Luxembourg became the first country to make public transport free for residents as well as tourists. This was done in order to reduce traffic congestion and air pollution since more than 200,000 commuters from neighbouring countries enter the country, in addition to those commuting within the country. A recent study using synthetic difference-in-differences found that this free public transport policy has led to an average reduction of around 8% in road transport CO2 emissions. This result was also confirmed by robustness checks that took into account various confounders like the COVID-19 pandemic, shifts in commuting behaviours and advancements in vehicle technologies.
Researchers from Spain analysed a policy where large discounts for transit services were provided in the country from 1st September, 2022. This was done as a part of a national plan to address the global energy crisis. The research suggests that while reducing transit prices is aimed at shifting from private to collective modes of transport for environmental benefits, such massive fare discounts may not be an efficient allocation of public funds. Another set of researchers leveraged a natural experiment in order to analyse the effect of 147 days of various public transport strikes on the concentration levels of key pollutants in Barcelona. They found out that public transport strikes led to a noticeable increase in the levels of the pollutants, suggesting that public transport was substituted for private vehicles.
Similarly, researchers analysed the effect of the ‘9-Euro-Ticket’ policy implemented in Germany from June until August 2022. The regional public transport was reduced to a flat rate of 9 Euros per month, representing a temporary and substantial reduction in fares. For example, the standard fare ticket in Berlin is normally priced at 86 Euros but this policy drastically reduced the fares to 9 Euros. Using Difference-in-Differences estimation, which compares the pollution levels before and after the policy, both, in treated and untreated regions, the authors found that this policy intervention causally reduced a benchmark air pollution index by more than six percent. This policy turned out to be a viable alternative for policymakers and city planners to improve air quality in spatially constrained cities.
What kind of policies might work best to reduce air pollution while increasing uptake of public transport? A study conducted by researchers in Beijing employed a Spatial Computable General Equilibrium (SCGE), a sophisticated simulation model to explore the outcomes of four distinct subsidy policies: fare subsidy, cash grants, road expansion, and public transport speedup, assessing their impact on citywide social welfare, jobs-housing spatial population distribution, and environmental outputs. Except for road capacity expansion, subsidy policies do not appear to reduce travel-related CO2 emissions; in fact, fare subsidy, cash grant, and public transport speedup policies all stimulate higher travel frequency, thereby increasing CO2 emissions. This comprehensive analysis provides valuable insights for policymakers on the effectiveness of various transport subsidy policies in achieving economic and environmental objectives. Contrast this with Thailand; at the beginning of 2025, Thailand was ranked as the world's 14th most polluted city according to the Swiss air quality monitoring services. In response, the authorities offered free public transport for a week to increase bus and electric train ridership and decrease air pollution. Through this temporary initiative they observed ridership in buses and electric trains rising by more than a third, with an accompanying reduction in air pollution. While its long-term effectiveness is still being evaluated, other ASEAN countries have started exploring investments in public transportation, with more measured approaches such as investing in low-carbon transport policies.
Through this, we can conclude that more empirical evidence is needed to fully understand the social benefits of transit investments and to inform policy decisions on sustainable urban transportation. This blog calls for careful consideration of local contexts, regulatory frameworks, and potential behavioral adaptations in planning and evaluating public transit investments, as well as forming successful policies that have a positive impact on air pollution.
Netra Damani
