The 99% Invisible City: A Field Guide to the Hidden World of Everyday Design

by Roman Mars

In many prewar suburbs, roadside trees were arrayed along verges between car-filled streets and pedestrian sidewalks. In postwar suburbs, some planners were concerned about the collision risks posed by this roadside greenery and began to experiment with putting trees on the other side of the sidewalk. Clearing out objects that could cause damage in collisions seems sensible on the surface, but it can have certain unintended side effects, like creating the visual impression of a wider paved area for drivers. More open roads encourage faster travel thanks to reduced “edge friction” from peripheral objects. A reduced number of obstacles also exposes pedestrians to increased danger when speeding vehicles swerve off roads. All of this points to a larger traffic engineering issue: people tend to use what’s given to them. Presented with wide open spaces, drivers will go faster.