A narrow pedestrian path through a snow bank over the curb. Typically, just the width of a boot.
Snow plows move snow to banks beside the road and sidewalks are shoveled but pedestrians crossing the road are often forced to trample their way through the snow bank. To avoid getting a boot full of snow, people will walk in the footsteps created by others who have gone before creating an ad hoc curb canyon.
In the spring when snow is melting curb canyons crop up as people prefer pioneering a new route over the snow bank rather than the pool of frigid water that can accumulate at official crossing points.
Crossing Bloor St, people walked single file through the curb canyon.