The Federal-Aid Highway Act of 1956 called for the construction of 41,000 miles of interstate highway by 1970 and created the Highway Trust Fund to finance it. From the mid-1950s to the early 1970s, the Interstate Highway System transformed US urban landscapes. Urban planners saw the urban freeway as a solution to growing traffic congestion in cities, as well as a tool to achieve the urban renewal goal of “slum” clearance [1
]. Planners and engineers decided where freeways would be built, with little to no citizen oversight [3
]. Freeway construction resulted in the demolition, division, and forced removal of poor communities of color, particularly African-Americans [1
]. Freeways facilitated white flight and accelerated white suburbanization [6
], reinforced racial residential segregation [6
], and increased air and noise pollution [9
], mostly in communities of color. Racial borders achieved through discriminatory race-based planning processes, such as redlining, restrictive covenants, and zoning [11
], were concretized into the built environment with freeway construction. The adverse effects of freeway construction are environmental justice issues [9
Freeway removal or rerouting is viewed as an opportunity to redress the health and environmental impacts of freeway construction [2
]. Teardown advocates seek to reroute freeways through alternative corridors or bury them in tunnels or trenches. For communities near freeways, this practice has significant implications for addressing traffic-related air pollution and associated adverse health effects, including asthma exacerbation, lung impairment, impacts on fertility and birth outcomes, and cardiovascular and respiratory mortality [17
]. A quantitative analysis of the air quality benefits of freeway removal is needed. Projects often involve building street-level boulevards in the former corridor. Transforming the former freeway alignment into a landscaped boulevard also increases urban green space. Green space has health benefits, such as increased physical activity and psychological well-being [20
]. However, a potential unintended consequence of efforts to expand urban green space is the green space paradox [20
]. Urban green space, aimed at addressing environmental injustice, can make a neighborhood more desirable, potentially leading to gentrification and the displacement of the residents for whom the green space was created. This paradoxical situation has been termed environmental gentrification [21
]. Studies indicate that freeway removal or tunneling can increase property values [2
]. However, the relationship between freeway removal and gentrification is largely unexplored in the peer-reviewed literature. One study assessed the change in neighborhood racial composition along an old freeway alignment replaced with a boulevard and found an increase in the percentage of white population and a decrease in the percentage of Black population [23
]. More research is needed to investigate how freeway removal or rerouting, and conversion of the old alignment to a boulevard, affect demographic and socioeconomic change.
In West Oakland, residents successfully advocated for rerouting the Cypress Freeway and creating a street-level boulevard along the original alignment. West Oakland, a redlined neighborhood [25
] and one of the few East Bay neighborhoods where African-Americans could own homes [26
], was targeted for, and adversely affected by, freeway construction. In 1958, the elevated, double-decked Cypress Freeway (I-880) was completed. It bisected West Oakland and physically segregated the neighborhood. Construction of the Cypress Freeway led to property demolitions and displaced 600 families [27
]. The later-constructed Grove Shafter (I-980) and MacArthur (I-580) Freeways further segregated the neighborhood. Freeway construction and other urban renewal projects in West Oakland destroyed over 5000 housing units and resulted in economic decline in the area [26
When the Cypress Freeway collapsed during the 1989 Loma Prieta earthquake, the California Department of Transportation (Caltrans) favored a rebuild option on the same alignment [16
]. However, legislation such as the National Environmental Protection Act of 1969 provided the community with the opportunity to participate in the decision-making process, an option that was not previously available. Community activists organized to oppose reconstruction along the original route and redress economic and environmental justice issues [16
]. After the public comment period for the draft environmental impact statement closed in 1991, Caltrans selected an alternative route around the perimeter of West Oakland, in an industrial area (Figure 1
). Some felt the proposal did not adequately address local concerns and filed a discrimination suit, under Title VI of the Civil Rights Act of 1964 [16
]. The case, Clean Air Alternative Coalition v United States Department of Transportation
, was settled out of court and resulted in several additional mitigation measures [16
], including the transformation of the former Cypress Freeway route into a landscaped boulevard, later named Mandela Parkway. Construction of Mandela Parkway began in 2002 and was completed in 2005.
In this study, we investigate the air pollution and neighborhood impacts of rerouting the Cypress Freeway and constructing a street-level boulevard in West Oakland. Our specific objectives are to: (i) quantify the local effects on air pollution of rerouting the Cypress Freeway, through modeling near-roadway concentrations for two different rebuild scenarios, and (ii) examine neighborhood socioeconomic and demographic impacts, as reflected by spatiotemporal changes in indicators of gentrification, to assess whether existing residents benefit from the freeway-to-boulevard conversion, or are excluded through the phenomenon of environmental gentrification.
West Oakland residents saw rerouting of the Cypress Freeway and replacement with a street-level boulevard as an opportunity to mitigate the air pollution burden that freeway construction had caused in their neighborhood and increase access to urban green space. Our air pollution maps and distance–decay curves reveal that rerouting the Cypress Freeway resulted in substantial reductions in annual average NOx and BC concentrations in the middle of West Oakland when compared to the Cypress Freeway rebuild-in-place scenario. These air quality benefits highlight the importance of roadway types planned through residential neighborhoods, such as freeways and designated truck routes. We observe that the new freeway route still impacts air pollutant levels in the Mandela Parkway corridor, so it is critical to select an alternative route that does not have segments in close proximity to residential areas. Limitations may be present in port communities and communities impacted by goods-movement activities.
Environmental justice activism sometimes has unintended paradoxical consequences, where efforts to improve a neighborhood make existing residents vulnerable to displacement [21
]. This displacement is facilitated through economic revitalization efforts that do not prioritize the needs of existing residents. While the urban freeway was thought of as a tool for urban revitalization by mid-century transportation planners, the removal and rerouting of the urban freeway are viewed as opportunities for redevelopment. An investigation of West Oakland indicates that freeway rerouting and construction of a street-level boulevard result in some environmental gentrification, with property value increases and the displacement of long-time Black residents, similar to freeway removal and tunneling. To ensure existing residents benefit from the air pollution reductions caused by freeway rerouting, affordable housing and other anti-displacement strategies, such as inclusionary zoning and renter protections, should be instituted [58
There are some limitations in our analysis methods. Traffic counts on the Mandela Parkway were based on a short-duration traffic survey. These counts were extrapolated to annual counts, using temporal allocation factors from McDonald et al. [37
] that were derived from freeway traffic count data. Although traffic activity profiles can vary by roadway type [59
], data on arterial traffic patterns were not available. More extensive traffic count data on local arterials is needed to improve estimates of the air quality impacts of freeway rerouting. Additionally, our analysis of neighborhood change was conducted at the tract level. Using an area-weighting method to estimate demographic and socioeconomic variables along the Mandela Parkway introduces error. As freeway removal and replacement with a street-level boulevard receives increased attention as a contemporary urban transportation policy, due to aging freeway infrastructure [10
], it is critical to accurately determine who benefits from such urban green space projects.