The first objective of this study was to test the performance of our localized walkability measure for which we calculated values from data we collected at the census block level and imputed values to the remaining census blocks in San Francisco City-County. Our walkability index closely corresponded to neighborhood Walk Scores® and the results make logical sense given the cultural and physical topographies of SFC. Thus, designing a stratified or simple random sample of neighborhood geographies, depending on study objective or outcome of interest, and imputing the values from the sample geographies to the larger region may be an efficient and accurate way to evaluate local environments for health behavior. We sampled census blocks in our design to obtain observational data at a very fine scale, which provides a level of detail to build from that data collection in larger administrative or observed boundaries may not. Such local specification may ensure more accuracy in imputed results as well as more specific local targets for policy and behavioral interventions.
We also hypothesized in this study first, that neighborhoods with larger proportions of residents racialized as Black, Asian and Latino, and second, neighborhoods with lower educational attainment than average, would also have significantly lower walkability scores. Regarding our first hypothesis, we did find significant inverse relationships between walkability and the percentage of non-Hispanic Black and non-Hispanic Asian residents, but not for Latino residents. Our second hypothesis proved apt for most neighborhoods; educational attainment was positively associated with walkability across the county, except in the Mission/Potrero Hill, the Outer Mission, Outer Sunset, and Parkside where there was no significant relationship.
In terms of overall walkability, most of the census block groups were within one standard deviation of the mean value for our dataset. Additionally, a large majority of the census block groups had walkability values greater than the median value for our dataset. These results speak to San Francisco’s status as one of the nation’s most walkable cities.28 However, despite generally high levels of walkability, there are still notable sociodemographic inequities between neighborhoods.
There are very clear differences in sociodemographic characteristics between the areas with greater walkability, average walkability, and lower than average walkability (shown in purple, white and green in Fig. 1, respectively), which likely explain our results in part. Supplemental Table 1 includes 2015–2019 ACS estimates of these characteristics, showing that the percentage of non-Hispanic White residents in the average walkability areas was 160% higher than in the less walkable neighborhoods, and 75% higher in the most walkable neighborhoods. Alternatively, the non-Hispanic Black population concentration drops 81% between the low and average walkability neighborhoods and drops a further 12% from the average to high walkability neighborhoods. Interestingly, the low and average walkability neighborhoods share a similar proportion of non-Hispanic Asian residents (44.7% low, 43.4% average), while the high walkability areas have a much lower percentage of non-Hispanic Asian residents (18.5%), which partially explains the significant inverse association between walkability and percentage of non-Hispanic Asian residents across the county. Median income in the lowest walkability neighborhoods was $74,880 compared to $113,572 in the average walkability neighborhoods and $148,776 in the most walkable neighborhoods. The percentages of residents below 200% of poverty were 33%, 21% and 16% respectively.
Bayview Hunters Point and Western Addition, two of the neighborhoods with lower than average walkability were also neighborhoods with the highest proportions of non-Hispanic Black residents, which have also been neighborhoods historically designated as “Hazardous” or “Definitely Declining” in the era of federal redlining, preventing issuance of government-backed home loans in the neighborhood.29 Although redlining is technically illegal today, disinvestment in these communities has continued across decades, which impacts features like walkability through a lack of government funding and resources to support new business development, green space, street maintenance, and general neighborhood upkeep.30 Additionally, the Bayview Hunters Point neighborhood is a heavily industrialized “sacrifice zone,”31 with an abandoned naval shipyard designated as a Superfund site, more than 150 brownfields, the former Candlestick Park stadium, which has been torn down but not remediated, and a sewage treatment plant that treats more than 80% of San Francisco’s sewage.32 These factors reduce aesthetic value for walking and expose residents to excessive risk of air pollution while also reducing home and property values, keeping people in place.32
Non-Hispanic Asian residents have not been as segregated as Non-Hispanic Black residents in San Francisco; however, between 2000 and 2020 they lost ground in the more walkable neighborhoods, as shown in Supplemental Figs. 1a and 1b, expanded further into less walkable neighborhoods, and have historically resided in a semicircle around the outsides of the most walkable neighborhoods that cluster in the city center. The infusion of technology funding and salaries over the past two decades, the increase in short-term rental properties, foreign investment in local property, and failures to expand affordable housing have priced many communities out of the neighborhoods in which they have resided for generations.33–35 This has pushed long-term and intergenerational residents to less desirable neighborhoods with fewer amenities, less aesthetic appeal, and greater exposure to hazards. Our walkability index provides an initial indicator of these inequities while also providing a more direct assessment of health promoting behavior. Engaging in urban planning activities designed to improve walkability may have ripple effects that increase overall neighborhood wellness. The point at which this becomes a trigger for gentrification, however, is a concern and remains to be seen.
There are a few limitations to our study. First, our walkability index was derived from a local observational study of neighborhoods in the Bay Area, an area with distinct topography, architecture, and population composition, and the results may not be generalizable to other cities in the US. However, we contend that the method certainly could be applied in other cities and towns where researchers, public health professionals, and policymakers are interested in collecting local data how their own built environments may be improved for health and wellness. A second limitation was that our research assistants who collected the neighborhood data, though they lived in the study area, did not reside in most of the surveyed blocks, and they completed neighborhood audits based on their own perceptions of the census blocks they surveyed. This may introduce bias as it cannot accurately capture the residents’ perceptions of walkability for their own neighborhoods. Nevertheless, the method we employed is a relatively efficient and affordable way to measure neighborhoods for health behavior across an urban area, and in this case, correlated well with sociodemographic inequities in San Francisco.