The heat penalty of walkable neighbourhoods.

"Walkability" or walking-friendliness is generally considered a favourable attribute of a neighbourhood that supports physical activity and improves health outcomes. Walkable neighbourhoods tend to have high-density infrastructure and relatively high amounts of concrete and pavement for sidewalks and streets, all of which can elevate local urban temperatures. The objective of this study was to assess whether there is a "heat penalty" associated with more walkable neighbourhoods in Montréal, Québec, Canada, using air temperature measurements taken in real time at street level during a heat event. The mean temperature of "Car-Dependent" neighbourhoods was 26.2 °C (95% CI 25.8, 26.6) whereas the mean temperature of "Walker's Paradise" neighbourhoods was 27.9 °C (95% CI 27.8, 28.1)-a difference of 1.7 °C (95% CI 1.3, 2.0). There was a strong association between higher walkability of Montréal neighbourhoods and elevated temperature (r = 0.61, p < 0.01); suggestive of a heat penalty for walkable neighbourhoods. Planning solutions that support increased walking-friendliness of neighbourhoods should consider simultaneous strategies to mitigate heat to reduce potential health consequences of the heat penalty.