A study by researchers from the National University of Singapore (NUS) and the University of São Paulo revealed that a beltway constructed to divert heavy-duty diesel vehicles traffic in the Brazilian city of São Paulo improved air quality and public health in the city. The study was published in the Journal of the European Economic Association.

The positive health outcomes of the intervention could guide the formulation of similar transport polices in other cities, where humans and diesel vehicles reside and transit in close proximity.

In 2010, São Paulo constructed a beltway along sparsely populated areas that are 25 kilometers away from the city center. The original intent of building the beltway was to enable heavy-duty vehicles to bypass the densely populated neighborhoods, and thereby ease traffic congestion in the inner-city roads.

While the intervention did immediately relieve road congestion by 20%, the NUS researchers found that the effect was short-lived as passenger cars quickly replaced the inner-city road space which the heavy-duty vehicles had left behind.

However, the researchers also found that the replacement of heavy-duty diesel vehicles with gasoline-ethanol passenger cars on the inner-city roads resulted in a sustained drop in the level of nitrogen oxides in the air, reducing air pollution in the city even after the traffic congestion rebounded.

Exploiting the inauguration of a beltway that removed 20,000 cargo trucks passing daily through inner-city roads in São Paulo, we examine the spatially differentiated impacts on the megacity’s traffic, air quality and public health. We combine rich panel data on road congestion, ambient NO_x concentrations (as a signature of diesel exhaust), and hospital admissions and deaths. The policy reduced congestion, pollution, and hospitalizations, with effects attenuating at increasing distances from a key inner-city corridor used by the transit trucks prior to the beltway opening.

The change in congestion was transient, as gasoline–ethanol passenger cars responded by filling the space the diesel trucks left behind. Effects on air and health persisted thanks to the compositional change in road users.

—He et al.

The improved air quality in São Paulo also translated into long-lasting positive health outcomes for its residents. The researchers observed that the compositional change in traffic in the inner-city roads resulting from the beltway’s diversion of diesel vehicles led to an overall estimated reduction of 5,000 hospital admissions associated with respiratory and cardiovascular illness every year.

The researchers estimated that about one annual premature death results for every 100-200 diesel trucks using inner-city roads.

The unintentional improvement in air quality and public health resulting from the São Paulo beltway demonstrates how judicious transport policies can benefit public health. Other world megacities such as London, Paris, New Delhi and Singapore may stand to gain similarly by limiting the circulation of diesel vehicles in the cities, particularly during the day when people are out and about.

—NUS Associate Professor Alberto Salvo, study leader

Like São Paulo, many major cities in the world have large volumes of diesel trucks, buses and vans transiting in close proximity with people, resulting in similar levels of air pollution. For example, nearly 40% of London’s total NO_x emissions is attributed to diesel vehicles. Relative to North America, Europe’s households have significantly adopted diesel cars over gasoline and alternative fuels.

Different cities may adopt different abatement strategies, such as the Ultra-Low Emission Zone charge in London and the temporary ban on diesel cars in Oslo. Therefore, it is crucial that policymakers evaluate a range of policies in order to select a combination of strategies most effective for their cities, the NUS researchers said.

São Paulo’s beltway construction provides a rare example, at the scale of a real-world metropolis, of the air and health benefits from shifting the urban transportation fuel mix away from diesel. Policymakers in other cities where human exposure to diesel runs high may learn from São Paulo’s experience.

Resources

• Jiaxiu He, Nelson Gouveia, Alberto Salvo (2018) “External Effects of Diesel Trucks Circulating Inside the São Paulo Megacity ” Journal of the European Economic Association doi: 10.1093/jeea/jvy015