Will making neighborhoods more walkable make people more active?
Probably, but it's hard to prove causality.
Neighborhoods are considered walkable if they have features that are well suited for getting around on foot: high density, a mix of homes and non-residential destinations, well-connected streets and paths. In theory, walkable neighborhoods should encourage people to walk more. But in practice, it's hard to know whether changes to the built environment change people's behavior.
There's strong evidence that walking is correlated with living in a walkable area. Studies using accelerometers to measure activity levels show that, compared to similar peers elsewhere, people in neighborhoods with accessible shops, parks, transit hubs and other pedestrian-friendly features are more active. By one estimate, they average 766 additional steps per day.
The issue is that walkable neighborhoods might attract, rather than create, walkers. If that's the case, investing in pedestrian-friendly development won't necessarily pay off in increased activity levels.
One study that followed participants over several years found that people who moved to more walkable neighborhoods reported walking more than they used to. But that result is probably biased by self-selection: people inclined to walk more might choose to move to more walkable areas.
So, there's reason to be optimistic that pedestrian-friendly development will make people more active, but so far the evidence is only suggestive.