摘要：Objectives. To examine health benefits and cost-effectiveness of implementing a freeway deck park to increase urban green space. Methods. Using the Cross-Bronx Expressway in New York City as a case study, we explored the cost-effectiveness of implementing deck parks. We built a microsimulation model that included increased exercise, fewer accidents, and less pollution as well as the cost of implementation and maintenance of the park. We estimated both the quality-adjusted life years gained and the societal costs for 2017. Results. Implementation of a deck park over sunken parts of Cross-Bronx Expressway appeared to save both lives and money. Savings were realized for 84% of Monte Carlo simulations. Conclusions. In a rapidly urbanizing world, reclaiming green space through deck parks can bring health benefits alongside economic savings over the long term. Public Health Implications. Policymakers are seeking ways to create cross-sectorial synergies that might improve both quality of urban life and health. However, such projects are very expensive, and there is little information on their return of investment. Our analysis showed that deck parks produce exceptional value when implemented over below-grade sections of road. As the world urbanizes, green space—such as parks in which residents can exercise and enjoy nature—becomes increasingly important for well-being. 1 It also increasingly becomes a scarce commodity. One option for increasing green space is for cities to cover major roadways with parks. Such parks are variously known as “freeway cap parks,” “deck parks,” or simply “freeway parks.” 2–5 This process has been tried in contexts as diverse as Santiago, Chile, 6,7 and Boston, Massachusetts. 4,8,9 Deck parks can produce multiple health benefits. Most notably, they remove contact between pedestrians and automobiles. In doing so, they not only reduce accidents but they also encourage active, pollution-free transportation such as biking or jogging. Deck parks also place vehicles in a tunnel, thereby reducing noise and air pollution in surrounding neighborhoods. Finally, deck parks provide green space in which people can exercise and relax. 10–13 In doing so, deck parks have the potential to reduce diabetes, heart disease, mental illness, cancer, low birth weight, and death associated with accidents. 14–22 They can also have positive impacts on property values. 23–27 However, such projects come with huge costs. On one extreme, there was the “Big Dig” in Boston. This project resulted in the creation of 5 urban parks. It also hid a 1.5-mile swath of freeway in the city’s urban center. This revitalized the area, producing vibrant and green pedestrian areas with shopping. 8,26 However, the Big Dig was plagued by problems, such as leaking tunnels and ceiling collapses, and the initial investment may run well over $20 billion by the time interest is paid. 8,9,28 The price tag was so high in part because the project involved burying a highway that was elevated. There are also more feasible projects, in which highways are already below ground or are at ground level. These can more easily be covered with an elevated park. One example of a successful above-grade deck park is Freeway Park in Seattle, Washington, which came at a relatively low cost of $18 million per acre and has become a centerpiece of the city (even as it sits atop 8 lanes of freeway). 29,30 There could be many projects that are easier still to complete because the freeway itself is below grade and can therefore be capped without much disruption to traffic. Despite the advantages of deck parks, it is rare that such projects are undertaken. This is in part because areas with major roadways tend to have lower property values and in part because green space tends to be a lower-priority investment in cities struggling to provide essential services to their citizens, such as health, welfare, and transportation. 23 Officials often overlook the potential for deck parks to prevent these very problems. Such projects have the potential to serve as powerful public health and transportation investments for low-income communities. We estimated the cost-effectiveness of such investments with the Cross-Bronx Expressway as a case study for deck park implementation. We chose this as a case study because it exemplifies a type of low-cost public works project for a low-income community. We also conducted a 1-way sensitivity analysis on the implementation cost so that our results can be compared with more ambitious projects in other localities. The Cross-Bronx Expressway is below grade (lower than ground level) and therefore inexpensive to cap. It is a major contributor to both air pollution and noise pollution. The expressway has been implicated in a crime wave that began in the 1970s and from which the South Bronx has still not recovered. 31–34 It wraps through areas with some of the highest prevalence of diabetes, obesity, and asthma in the city. 33 If capping the Cross-Bronx Expressway with a deck park proves to be cost-effective (the health benefits coming at a reasonable cost relative to other health investments), then it could serve as a starting point for examining other projects nationwide. However, choosing an inexpensive and politically viable example does not guarantee that implementation of a deck park will go as planned. We therefore chose to include the most conservative estimates of health benefits and the highest published estimates of costs for similar projects to ensure that any benefits are likely to be realized in the real world. The resulting analysis is biased against the use of deck parks, thereby ensuring the estimate that we generate is a reasonable starting point from which to evaluate such public works projects.
