Beyond Measuring Access to Destinations

with Huijun Tan
For some time, researchers and professionals have advocated for a paradigm shift in transportation that focuses on access rather than mobility, as expressed here by Todd Litman or explained in this video by Dr. Susan Handy. This recognizes that the purpose of transportation is to provide access; it is not just travel for travel’s sake. In technical jargon, transportation is a derived demand, which is a term that emphasizes that transportation responds to household and land use characteristics.
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The benefit of this approach is that it de-centers the mobility strategies that have not produced healthy or sustainable outcomes—or even effectively solved mobility goals (looking at you, induced demand). Prioritizing mobility and speed, for example, has serious safety consequences. In a recent analysis of pedestrian traffic fatality hotspots, nearly all fatalities occurred on multi-lane arterials (which are designed for automobility), with 70% requiring pedestrians to cross five or more lanes.

After decades of conceptualizing and measuring accessibility*(aka access to destinations) in academia, there is growing acceptance of the idea in practice. Some version of this concept has been described as creating complete neighborhoods or as 20-minute neighborhoods. However, Paris Mayor Anne Hidalgo’s plan for the 15-minute city (also called a city of proximities) has captured international attention and generated conversation about accessibility.

Part of this conversation also includes some skepticism about the feasibility and fairness of this model, particularly for American cities with land use and transportation patterns that make it difficult to get to any destinations by walking or bicycling. Another critique is that the 15-minute city excludes people with disabilities owing in part to the economic inaccessibility of existing complete neighborhoods. Edward Glaeser argues that a 15-minute city does not provide enough economic opportunity for residents; residents need access to the entire metropolis within an hour's time.

Another factor to consider is perceived accessibility. Measuring access to destinations through objective means has been computationally difficult until relatively recently. Today, practitioners have a number of tools at their disposal. These tools typically define access as the destinations closest to residents, but do people travel to the closest grocery store, as a gravity model would suggest? Or do they choose the store with lower prices or the store with more options? What if the route to the closest destination feels unsafe because of traffic or personal security concerns?

The conceptual issue, which some of the 15-minute city critiques approach, is that measures of accessibility represent potential access to destinations. They don’t represent actual travel behavior or whether resident needs have been met. For example, planners could use typical approaches to measuring accessibility to determine whether there are any food deserts in the city. However, objectively measured accessibility doesn’t capture whether stores are affordable to residents or sell culturally relevant foods. Perhaps the problem is not a food desert, but a food mirage.

Here are some recommendations for analyzing complete neighborhoods:

• Understand the actual travel needs and barriers of residents, particularly historically excluded populations whose travel patterns are not reflected in travel surveys, through a meaningful community engagement process
• Ground-truth accessibility analysis results with residents to understand whether it reflects their sense of accessibility—or whether you actually have an access mirage
• If you have the technical wherewithal, explore models (e.g., multinomial logit) that can account for destination preferences

The climate and health benefits of complete neighborhoods are clear—they increase opportunities for physical activity as part of daily life and reduce the need for driving, which is likely to reduce greenhouse gas emissions and air pollutants. There’s also a good chance that they will create more attractive and safer neighborhoods. Many low-income communities and communities of color have reduced access to resources owing to inequitable planning and policy decisions. Improving access to destinations should be prioritized for these communities. Planners must ensure that these existing residents benefit from improvements. Methods for analyzing the risk of displacement and case studies for preventing displacement can be found on Streetsmart’s Equity and Inclusion page.

We mustn't treat the 15-minute neighborhood (local accessibility) and access to the larger metropolis (regional accessibility) as mutually exclusive paths—we need both for climate, health, and equity.

* Unfortunately, the transportation field uses the term accessibility in two different ways: one is access to destinations, the subject here, and the other is accessibility for people with disabilities. Any efforts to improve local access to destinations should ensure that it meets the needs of people with disabilities.