Healthy Community Design, Anti-displacement, and Equity Strategies in the USA: A Scoping Review

Recent investments in built environment infrastructure to create healthy communities have highlighted the need for equity and environmental justice. Although the benefits of healthy community design (e.g., connecting transportation systems and land use changes) are well established, some reports suggest that these changes may increase property values. These increases can raise the risk of displacement for people with low incomes and/or who are from racial and ethnic minority groups, who would then miss out on benefits from changes in community design. This review scanned the literature for displacement mitigation and prevention measures, with the goal of providing a compilation of available strategies for a wide range of audiences including public health practitioners. A CDC librarian searched the Medline, EbscoHost, Scopus, and ProQuest Central databases, and we identified grey literature using Google and Google Scholar searches. The indexed literature search identified 6 articles, and the grey literature scan added 18 articles. From these 24 total articles, we identified 141 mitigation and prevention strategies for displacement and thematically characterized each by domain using an adapted existing typology. This work provides a well-categorized inventory for practitioners and sets the stage for future evaluation research on the implementation of strategies and practices to reduce displacement.


Introduction
Neighborhood development has been described as a means to elicit social, economic, political, and environmental change in communities in response to dismal conditions and areas in decline [1]. Neighborhood development investments may be federally funded initiatives such as Community Development Block Grants, but can also be driven by community members or non-profit organizations [2]. Historically, these strategies have focused on improving social and economic outcomes [3], typically in the form of ensuring housing and providing social services. Recently, there has been a shift and focus on neighborhood development as a way to support built environment infrastructure for healthy living [2,4,5]. Specifically, there have been historic investments in infrastructure from the federal government, including the Bipartisan Infrastructure Law [6], Justice40 Initiative [7], and the American Rescue Plan [8]. These investments have been put in place to tackle issues of environmental justice, the COVID-19 pandemic, and the overall health and well-being of communities.
A specific example of how these infrastructure improvements may influence health includes the Community Preventive Services Task Force (CPSTF) recommendation for built environment approaches to increase physical activity that combine infrastructure modifications for transportation with changes in land use and community design, such as adding sidewalks and bicycle lanes, expanding public transit, improving parks and recreation facilities, and allowing residential density and mixed-use development that enables housing in proximity to destinations such as businesses and schools [9]. These recommendations have been translated by CDC's Active People, Healthy Nation Initiative into a strategy called "activity-friendly routes to everyday destinations" and they may be especially beneficial to communities with people of lower incomes or who are from racial and ethnic minority groups, who some studies have shown may live in neighborhoods lacking built environment features that support physical activity (e.g., homes close to parks, schools and jobs; safe walking and biking routes; expanded public transit), while also facing disparities in car access [10][11][12]. Additionally, similar built environment strategies have been shown to mitigate urban heat island effects [13], and facilitate community resilience [14]. Communities with people of lower incomes or who are from racial and ethnic minority groups also have higher rates of physical inactivity and chronic diseases, such as cardiovascular disease [15,16].
However, built environment modifications intended to improve health for communities with people of lower incomes or from racial and ethnic minority groups may result in differential negative impacts [17]. There are mixed findings on how infrastructure changes related to physical activity have impacted property values and displacement. The concept of residential displacement was proposed by Grier and Grier [18] and is described as occurring "when any household is forced to move from its residence by conditions which affect the dwelling or immediate surroundings, and which (1) are beyond the household's reasonable ability to control or prevent; (2) occur despite the household's having met all previously-imposed conditions of occupancy; and (3) make continued occupancy by that household impossible, hazardous or unaffordable." Similarly, commercial displacement is the process by which low-value businesses become displaced with the introduction of higher value businesses or up-scale housing [19]. Physical displacement has relatively obvious, negative social and economic impacts, such as a loss of a preferred residence, social networks, housing stability, and educational opportunity. Studies on activity-friendly routes for bicycling showed a positive association with property values, but no association with displacement [20,21]. Close proximity to light rail transit stations may drive displacement [22]. Additionally, increasing access to green space in urban areas has been linked to increased gentrification [23,24]. The term "gentrification" is contested and has evolved across geospatial and historical contexts [25,26]. The term was first used by the sociologist Ruth Glass in the 1960s, who described working class quarters of London being "invaded by the middle classes -upper and lower" [27]. While the original use focused on class, contemporary definitions of gentrification, particularly in the US context, incorporate both class and race and increasingly recognize structural economic inequities and social and political complexities. For example, a recent systematic review of gentrification and health outcomes research in the US-defined gentrification as "an interactive process in formerly declining, under-resourced, predominantly minority neighborhoods involving economic investment and increasing sources of capital infusion and inmigration of new residents, generally with a higher socio-economic status" [28]. Gentrification has also been studied as a process that may worsen existing health disparities [29][30][31]. For example, a recent systematic review on the health impacts of gentrification found that Black people and people with lower incomes living in gentrifying areas suffered negative effects including mental health disorders and poor self-rated health [32]. However, no longterm or robust assessments exist that document the impacts of investment in built environment infrastructure on gentrification or displacement.
Still, communities have valid concerns related to increased property values like increased rent or property taxes [20,[22][23][24]. To promote equitable distribution of costs and benefits in the context of built environment improvements to increase physical activity, efforts are needed to understand potential strategies to prevent displacement or mitigate its harms (hereafter "anti-displacement strategies") when investing in physical activity infrastructure. Much of the previous literature on strategies to prevent or mitigate displacement has focused on affordable housing [33,34]. However, affordable housing strategies may be insufficient to protect low-income residents in a context of increasing property values from which many cannot benefit [35]. Actions to prevent displacement may require multiple strategies utilizing a variety of tactics.
Therefore, the current review aims to (1) compile toolkits and resources to help practitioners learn about available anti-displacement strategies; (2) from these toolkits and resources characterize a broad range of anti-displacement strategies that have been proposed, implemented, and/or evaluated in the USA; and (3) discuss the implications of these strategies for centering equity in projects aiming to improve the built environment for healthy lifestyles.

Search Strategy
The present review consisted of a broad search for indexed literature, as well as a complementary grey literature scan. We consulted 10 experts in the field for background and context to inform our search strategy. To be included in this review, articles must have been published in the past 20 years (i.e., since 2002). This timeframe reflects the more recent emergence of literature in this field. The search strategy included key terms for "gentrification" or "displacement" or "urban renewal" and "mitigation" or "prevention". Indexed publications were identified in November 2021 by a CDC librarian from searches of the Medline, EbscoHost, Scopus, and ProQuest Central databases. A complementary grey literature scan via Google and Google Scholar was commenced in May 2018 and completed in April 2021 using the same key terms as the indexed literature search. Due to the importance of national and historic contexts related to displacement that are specific to the USA, we excluded non-US-based articles as well as non-English language articles. Additionally, to make both searches feasible within time and resource constraints, we included in both only articles, resources, toolkits, or best practice guides that contained more than one strategy. Protecting against displacement in most place likely requires multiple strategies in concert with each other that employ a variety of policies. From the indexed literature review, study title and abstract screenings were completed by four screeners (AS, HD, KG, and KI), with at least two screeners reviewing each.

Data Abstraction
We reviewed each included resource to identify any strategies that were proposed, implemented, or evaluated. We researched, as needed for presentation to public health audiences, strategies for which full descriptions were not included in the original sources. Three reviewers (KG, LR, and NS) abstracted data using a standardized form in Microsoft Excel and discussed and reconciled all discrepancies. Variables of interest included the strategy or measure identified, the definition of the strategy or measure, whether it related to residential and/or commercial displacement, and into which domain it best fit.

Results
Based on the search criteria, we identified 108 articles in the indexed literature and excluded 102 after abstract and full text reviews (Fig. 1). A total of six indexed articles met all eligibility requirements. The grey literature scan identified 280 potentially relevant documents, of which 224 were excluded because they did not include a list, toolkit, or review of strategies. The majority (70) of these 224 did not name specific anti-displacement strategies; 56 were news stories or blog posts; 51 dealt with measuring gentrification, displacement or risk; 47 were place-specific case studies, including three non-US places. We also excluded 38 documents that addressed single strategies. Thus, an additional 18 resources were identified from the grey literature scan for a total of 24 unique resources or articles. More information on each resource can be found in Table 2, including whether a resource was found in the peer-reviewed or grey literature, and the number of strategies per domain from each resource. The indexed literature search yielded only one journal publication and 5 academic products (i.e., dissertations, theses, or class papers), which we grouped with grey literature because they lacked peer review. Excluded grey and indexed literature (including two peer-reviewed papers) that only addressed single strategies would have added the following four    Though these were not added to stay consistent with our objectives and search strategy, this highlights the large percentage of strategies that were captured by our search. From these 24 resources, we identified and categorized 141 total anti-displacement strategies ( Table 3). Six of the nine domains were conceptually tied to affordable housing, and a similar majority of the strategies (62%) were categorized within those six; only stabilization, community engagement/education, and cross-cutting strategies addressed other factors. Of the 141 strategies, 81 addressed residential displacement, 53 both residential and commercial displacement, and seven commercial displacement only. More detail on each domain is provided below.

Domains of Anti-displacement Strategies
Preservation (n = 17) These strategies aim to preserve existing affordable rental units despite increasing property values [36]. This could come in two forms, either rent-restricted affordable units or unsubsidized affordable units. Conceptually, these strategies protect against displacement by ensuring a set amount of affordable housing options, which may or may not be intended for long-term residents. An example strategy would be preservation of federally subsidized affordable housing which include programs designated to preserve affordable housing units. Most strategies in this domain addressed residential displacement (n = 10), five addressed both residential and commercial displacement, and two addressed only commercial displacement.

Protection (n = 28)
These strategies focus on helping long-time renters, typically low-income households, who wish to stay in the neighborhood [36]. These strategies include legal protections for long-time renters, along with voluntary practices. An example is anti-harassment laws, which prevent landlords from coercing tenants into leaving. Protection strategies may also mitigate the impacts of displacement by helping long-time residents stay connected to neighborhoods. An example of protection through mitigation practices is transit subsidies                  for low-income households, which reduce barriers of long-time and low-income residents to stay connected to a neighborhood, despite the possibility of being physically displaced. Most of these strategies focus on residential displacement (n = 22); three targeted both residential and commercial displacement, and three only commercial displacement.
Inclusion (n = 9) These strategies focus on ensuring that new development or a share of new development will be affordable for the long term (30 or more years) [36]. This strategy is broad and addresses displacement by creating affordable housing possibilities in the context of new development. New affordable housing creates more options for long-time residents to stay in their neighborhoods. Inclusionary zoning policies, which create expectations of developers to include affordable housing, are the best known of these strategies and almost synonymous with the definition of this domain. Though most inclusionary policies are mandated, there are examples of voluntary inclusionary practices by developers. Most policies in this domain targeted residential displacement specifically (n = 7); one targeted both residential and commercial displacement, and one commercial displacement alone.

Revenue generation (n = 11)
This domain is also broad and leverages the growth and financial resources connected to new development and redevelopment towards ensuring funding for affordable housing [36]. Like inclusion, revenue generation aims to ensure a share of affordable housing possibilities within new development. Conceptually, this strategy creates more potential options for long-time residents to stay in their neighborhoods despite rising prices. A primary example of this is Tax Increment Financing (TIF), which uses the expected increases in property tax due to new development and public improvements to fund the new development itself. TIF mechanisms that establish requirements to use a portion of the funding for affordable housing can be a displacement prevention strategy. Most of the strategies identified in this domain targeted residential displacement (n = 8); three targeted commercial displacement.  Table 2 developers to create affordable housing by providing incentives that are often financial [36]. We added disincentives to the original typology to encompass strategies that discourage communities and developers from rapidly increasing rents or engaging in speculative housing strategies. Both strategies act against displacement by creating or maintaining affordable housing options. For example, state tax credits for affordable housing can reduce project financing costs and thus provide an incentive to develop affordable housing. Inversely, a tax on rent increases would be a disincentive to landlords from large rent increases. Ten of these strategies focused solely on residential displacement, and the remainder on both residential and commercial displacement.

Incentives/disincentives (n = 15) This domain includes strategies that encourage communities and
Property acquisition (n = 9) These strategies facilitate acquiring funding or sites for affordable housing, usually by nonprofit or community organizations [36]. Property acquisition strategies help accumulate funding or give priority to the public or nonprofit sector to acquire property that will be dedicated to affordable housing. These help protect against displacement by ensuring that housing will either stay or become affordable. An example of this is prioritizing public land for affordable multi-family housing and mixed use development. Two-thirds of the policies identified in this domain focused on residential displacement (n = 6), the remainder commercial displacement.

Stabilization (n = 18)
This domain includes strategies to increase stability for existing residents by securing and providing resources to become a home owner and help to maintain home ownership. These strategies may assist residents in pursuing home ownership, and empower residents with resources and assistance to stay in their neighborhoods. Stabilization efforts work towards ensuring long-term stability in housing, thus helping to protect against both the physical and cultural displacement of homeowners. One example is home ownership protection policies, which are financial assistance policies that help lowincome homeowners to keep their homes. All stabilization strategies we identified targeted residential displacement and seven also targeted commercial displacement.
Community engagement/education (n = 15) These strategies focus on educating and engaging with community members. Several relate to educating community members on affordable housing and homeownership processes. Others aim to ensure that longtime residents have a voice in any development or planning process. Examples of the latter include community organizing and supporting resident representation in planning processes. A majority of the strategies in this domain targeted both residential and commercial displacement; only two were focused solely on residential displacement.

Cross-cutting (n = 19)
This domain includes overarching policies or themes related to displacement or affordable housing. As such, most strategies targeted both commercial and residential displacement with only five focused solely on residential displacement. Strategies in this domain primarily targeted systemic issues related to displacement and frequently health disparities. One example is the practice of Health in All Policies (HIAPs), which strives to integrate health considerations of all communities into government practices.

Discussion
This review was conducted in response to inquiries from community-based public health practitioners, based on concerns from the populations they serve, who are often disproportionately affected by disparities in physical activity. It provides a comprehensive list of anti-displacement strategies and wellcategorized resources for learning more about how to address displacement concerns in the context of built environment changes to support healthy lifestyles.
To characterize a wide range of anti-displacement strategies, we adapted an analytical framework [36] and added domains to encompass the wide range of strategies we identified. We then placed each strategy within one of nine domains and characterized each domain with a brief description, including relevance for residential and commercial displacement domains. This scoping review comprehensively compiles existing strategies and resources with potential to protect against displacement, beyond affordable housing. Other reviews have focused solely on affordable housing [33], which is related to displacement but does not fully account for its complexities. Though not within the scope of our review, it is important to note the impact of displacement due to natural disasters, conflict, and crises. The current review provides high-level descriptions for a large number of strategies with potential to protect against displacement and makes these more easily accessible for a wide range of audiences including community-based public health practitioners.
It is important to note the limitations of the present study, including the potential exclusion of strategies based on our review's objectives. Additionally, the available evidence limited our ability to further characterize the identified strategies including being able to present information on facilitators and barriers of these anti-displacement strategies, as well as the main actors involved, among other details. This may be partially due to the lack of indexed peerreviewed manuscripts available. However, our project had multiple strengths, comprising a thorough review (including indexed and grey literature) and coding by multiple researchers. The greatest strength is the responsiveness to a need expressed regularly by public health practitioners to address community concerns about gentrification and displacement in connection with built environment changes. Our review provides a single, well-categorized inventory that can help practitioners appreciate the wide range of potential strategies. When built environment approaches are being considered, public health practitioners can then engage local expertise and lived experiences to select policies and practices best suited to increase health and equity in their local context.
We identified several remaining gaps upon completion of this study. One immediate need is further exploration of the relationship between gentrification, displacement, and projects aimed at improving the built environment for increased physical activity and healthy lifestyles. A majority of articles and resources found by our review came from the grey literature, highlighting a lack of peer-reviewed research on anti-displacement strategies. We did not conduct an evidence review, but we identified a prior systematic review of displacement prevention or mitigation studies published between 1980 and 2016 by Ghaffari et al. This review referenced 52 studies, of which we examined the full texts for 49; the remaining three studies were inaccessible by our library (2) or published in a language other than English (1). Of the 49 studies we examined, only 8 reported results from any evaluation and only 2 used quantitative, hypothesis-testing methods. Thus, our examination of a prior review with a different focus than ours highlights a gap related to public health evidence on the impact of anti-displacement strategies. Further evaluation of impacts on equity could also be useful to practitioners and community members faced with choosing among a wide variety of strategies.
Some strategies may be better suited than others when accounting for variations in for communities' land use regulations, and geographic, social, political, or population characteristics. Gentrification itself has been highlighted as a socially and economically beneficial change to an area that promotes inclusion and social mixing [60]. However, gentrification may lead to detrimental effects on a community including the potential to undermine social cohesion [61]. Some strategies may even exacerbate displacement within certain contexts. For example, historic preservation was identified in our review as an anti-displacement strategy, but has raised concerns about encouraging gentrification and displacement in some contexts [62][63][64][65]. Gaps still exist in which anti-displacement strategies might work best and promote equity in which locations.
Given widespread community concerns and some emerging evidence, preventing displacement is an important priority for health equity. As a result, it makes sense to present known practices for mitigating and preventing displacement while acknowledging their possible limitations [66]. It is also important to continue research to understand the dynamics of gentrification and displacement along with the impact of mitigation and prevention strategies.
More expansive and nuanced theoretical frameworks could inform research on the processes and pathways through which built-environment approaches influence health, health equity, gentrification, and displacement. Some theoretical work has overlooked differential impacts of built environment initiatives by income, race, or other social dimensions [17]. New theoretical frameworks could clarify knowledge gaps and promote exploration of disparate impacts for communities with people of lower incomes or from racial and ethnic minority groups [67][68][69]. Guided by more inclusive theories, future research could include harms that are distinct from the loss of a home. Frameworks are needed that include emotional attachment to places and social processes that attach intrinsic value to a specific geographic space [70,71]. Furthermore, accounting for and centering the lived experience of people and communities experiencing gentrification or displacement is essential to integrate into these new models. Given the time horizon of the health effects associated with built environment and economic changes, frameworks that consider the life courses of places and people may also be helpful [72].
Though gentrification and displacement of communities should not be overlooked, it is also important to note the usefulness of land use, community planning, and improved transportation systems for promoting health equity and combating racial inequities. There is recent expert consensus that transportation and land use policies that improve neighborhood accessibility, including complete streets policies are vital for health equity, when implemented with policies that protect communities including zoning reform and anti-displacement strategies [73][74][75]. Zoning reform has the potential for significant impact on health equity as it can influence community design that is beneficial for health, and simultaneously include protections for long-term residents (e.g., inclusionary zoning, affordable housing).

Conclusion
In this work, we have assembled and organized an extensive menu of strategies to prevent or mitigate displacement in communities considering or undergoing changes that include built environment interventions intended to promote physical activity and health. Built environment interventions hold substantial promise to improve health and reduce health disparities, but only if people of lower income and/ or from racial and ethnic minority groups, are able to remain and benefit from new development or infrastructure investments. The ability to design, create, and maintain amenities that encourage active living while preserving affordable, stable communities depends on creatively combining local knowledge with context-sensitive anti-displacement strategies. Ultimately, policy solutions to health disparities will require equity to be a central goal.