Pedestrian accessibility in grid layouts: the role of block, plot and street dimensions

Abstract

Research on urban form and walkability suggests that on average smaller blocks are better for pedestrians. We explore how block sizes, plot dimensions and street widths affect pedestrian accessibility in regular grids. Pedestrian accessibility is captured by the gravity index, which is proportional to the number of neighbouring plots that can be reached within a given walking radius and inversely proportional to the travel costs involved. Pedestrian accessibility is measured for the original town plans of well-known US and Australian grids and compared with thousands of computer simulated grids, analysing how close the grids come to the theoretical maxima of pedestrian accessibility, given plot sizes and street dimensions. The findings show how dimensions of plot frontages and depths, street widths and block lengths affect pedestrian accessibility in gridiron urban environments. Block lengths have a non-linear relationship to accessibility and smaller blocks are not necessarily better for pedestrians. In many cases, larger blocks have greater pedestrian accessibility than smaller blocks, which might explain previous variable findings on the effects of blocks sizes on walkability. Though block lengths in most of the famous grids we investigate come close to achieving maximum possible pedestrian accessibility levels, some of them could provide users with as much as 12 per cent more accessibility if their lengths were optimized for pedestrians. The lengths of the Manhattan and Indianapolis blocks come closest to maximizing pedestrian access, given their original plot and street dimensions. We illustrate a few prototypical block sizes that maximize pedestrian accessibility and may be suitable for pedestrian-friendly subdivisions in contemporary urban planning.