Ask most municipal engineers about walkability and they will point to sidewalks. And sidewalks matter: the absence of a safe, continuous pedestrian surface is a genuine barrier to walking. But walkability research over the past three decades has made clear that the sidewalk is only one layer of a much more complex system. Understanding that system is the first step toward building neighbourhoods where walking is not just possible but preferred.
The concept of the five Ds: density, diversity, design, destination accessibility, and distance to transit, emerged from the work of planners like Robert Cervero and Kara Kockelman in the 1990s and has been refined by researchers ever since. It offers a useful framework for thinking about why some neighbourhoods are walkable and others are not, even when both have sidewalks.
Density matters because it determines whether destinations are close enough to reach on foot. A neighbourhood of detached single-family homes on large lots may have excellent sidewalks, but if the nearest grocery store is two kilometres away, walking to it is impractical for most people. Missing middle housing, townhouses, duplexes, low-rise apartments, increases density without dramatically altering neighbourhood character and brings destinations within walking range.
Diversity refers to the mix of uses within a walkable catchment. The classic urban mixed-use model, retail at grade and residential above, creates destinations that generate foot traffic at different times of day and give people reasons to walk for multiple purposes in a single trip. A street with only one type of land use, however well-designed, cannot sustain walking the way a genuinely mixed street can.
Design encompasses the experiential quality of the pedestrian environment. Street trees are among the most powerful walkability interventions available: they provide shade, reduce perceived walking distance, buffer pedestrians from traffic, and create a sense of enclosure that makes streets feel more human in scale. Active frontages, meaning buildings whose ground floors engage with the street through windows, doors, and outdoor seating, are equally critical. A blank wall or a parking lot at grade is the enemy of walkability regardless of what the sidewalk behind it looks like.
Destination accessibility is the measure of how many useful places are reachable on foot within a given time threshold, typically five or fifteen minutes. This is the conceptual core of the fifteen-minute city model and reflects a fundamental truth: people walk to get somewhere, not to walk.
Finally, distance to transit matters because transit and walking are complementary. Every transit trip begins and ends on foot. Neighbourhoods well-served by transit tend to be walkable not because transit causes walkability, but because they share underlying conditions: density, mixed use, good design.
Walkability is not a feature that can be added after the fact with a sidewalk or a crosswalk. It is the cumulative result of land use decisions, building placement choices, street design standards, and programming that accumulates over time. The good news is that every project, every infill development, every streetscaping investment, every zoning amendment, is an opportunity to add another layer.