A sneckdown (or snowy neckdown) is a temporary curb extension caused by snowfall, where snow has built up in the road but not been flattened by traffic, effectively reshaping the curb. Sneckdowns show how the space is being used by vehicle and foot traffic, and may reveal points where a street could be usefully narrowed with neckdowns to slow motor vehicle speeds and shorten pedestrian crossing distances.

The term was coined by Streetsblog founder Aaron Naparstek in 2014,^[1][2] popularized by Streetfilms director Clarence Eckerson, Jr. and spread widely via social media.^[3] Other Twitter hashtags that have been used to describe snow-based traffic-calming measures include #plowza, #slushdown, #snovered and #snowspace.^[4]

In Philadelphia, Pennsylvania, at Baltimore and 48th Street, a sneckdown-inspired permanent upgrade to the pedestrian environment was made in 2011.^[5] In the 1980s, some planners in Australia distributed cake flour in intersections to observe patterns of vehicle movement hours later.^[4]

Documenting sneckdowns is an autographic design practice that takes advantage of the self-inscribing qualities of snow.^[6] The practice of using snow to trace the behavior of vehicles, pedestrians, and playing children was already described in Camillo Sitte's 1901 urban design treatise.^[7]