Quantifying health co-benefits: from shifting to more walking and cycling to urban climate action plans
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Abstract
Climate change and transportation are both “wicked problems” characterized by their complexity, interconnectedness, and the dynamic nature of how potential solutions are evaluated and compared. They both also have broad, multidisciplinary implications for society, ranging from health to financial to environmental injustice. While multidimensional in nature, solutions to these twin challenges are often not evaluated multidimensionally, with cost-benefit analyses exclusively comparing, for example, environmental impacts to infrastructure costs or transportation travel time savings to project costs, with health implications ignored. Health impact assessments can be an effective way to include quantifiable health implications in cost-benefit analyses or even introduce health impacts into the policy discourse when they might have otherwise been overlooked.
Transportation trips in the United States are dominated by single-occupancy vehicles, with implications for emissions, physical activity, and land use. Transitioning trips to active forms of transport, like walking and cycling, has the potential to reduce Transportation trips in the United States are dominated by single-occupancy vehicles, with implications for emissions, physical activity, and land use. Transitioning trips to active forms of transport, like walking and cycling, has the potential to reduce congestion, improve air quality, reduce greenhouse gas emissions, increase physical activity, open land to alternative uses, and improve health. It also has the potential to increase traffic fatalities, as these modes are more vulnerable than automobiles. However, typically these types of projects are evaluated from a policy perspective solely on the implications for the transportation system (e.g., travel time, congestion, wear and tear on roadways). Urban climate action plans, on the other hand, by their nature focus on mitigating greenhouse gas emissions that cause climate change and adapting urban areas to better manage the effects of a changing climate. However, because the sources of greenhouse gas emissions tend to also be sources of air pollution, these policies and interventions have the potential to affect local air quality and, with it, human health. In both cases – active transport polices and urban climate action plans – health effects are important “co-benefits” even if they are not the primary objective.
In this dissertation, we conduct three health impact assessments to quantify health co-benefits of policy measures not primarily targeting health. Chapter 2 focuses on the physical activity health co-benefits of transportation policy that is primarily focused on reducing greenhouse gas emissions and is implemented at the county-level across the East Coast. We used modeled shifts in total walking and cycling miles traveled to estimate the net mortality impacts of nine cap-and-invest scenarios that might have been implemented across 13 states in the Transportation Climate Initiative. We found that all scenarios modeled would reduce net mortality in all 378 counties included; however, impacts would be concentrated in urban areas along the I-95 corridor. The monetized value of mortality benefits was estimated to exceed the infrastructure costs of walking and cycling improvements for all scenarios.
Chapter 3 focuses on estimating the mortality impacts of shifting to more walking and cycling in the Greater Boston Area under different scenarios implemented at the individual level. We used data from the Massachusetts Travel Survey and the National Health and Nutrition Examination Survey to estimate baseline individual total physical activity for ~3 million residents of the Greater Boston Area. We then estimated mortality impacts from three different scenario concepts: 1) all residents meet the Surgeon General’s recommended activity level; 2) all residents increase activity by 15, 30, and 60 minutes more walking and cycling; and, 3) the City of Boston trip mode share shifts to match Amsterdam. We found that all scenarios had likely positive net mortality benefits. We found that scenarios that targeted the least active population had greater health impacts due to the non-linear nature of epidemiological concentration response functions used. We believe this suggests that individual modeling is helpful compared to aggregated population-level modeling when conducting similar studies.
Informed by the challenge of increased traffic fatalities associated with walking and cycling activity in Chapters 2 and 3, Chapter 4 describes the disparities by race/ethnicity in traffic fatalities per mile-traveled for walking, cycling, and driving. We found disparities in fatality rates across all modes, with Black and Hispanic Americans dying at higher rates per mile-traveled than White or Asian Americans. Our findings suggest that disparities are greater than previously reported, including in official federal documents, due to our novel adjustment for differential miles traveled by race/ethnicity. As a policy consideration, we suggest that policymakers consider ways to address both systematic racism and road safety with recently approved federal transportation infrastructure resources.
In the third health impact assessment (Chapter 5), we used air quality modeling to predict how fine particulate matter and ozone concentrations might shift across the region if only Boston eliminated emissions. We also estimated the mortality and morbidity health effects using U.S. EPA’s BenMAP program. We found that fine particulate matter would likely decrease across the region if Boston emissions were eliminated. Ozone concentrations, however, would likely increase in some areas and decrease in others, due to ozone’s more complex relationship with nitrogen dioxide. The net health impacts of eliminating Boston emissions would likely be large, and concentrated in non-Hispanic Black communities due to the environmental injustices present in current air quality.
Overall, this dissertation contributes to the growing evidence base that documents the health co-benefits of transportation and climate action. We believe our findings suggest that policymakers would benefit from requiring consideration of how potential policies and programs affect the public’s health, even when health impacts are ancillary to primary policy or programmatic objectives.