The concept of “clear zones” is sometimes cited in the highway design process. A clear zone represents an unobstructed, traversable area beyond the traveled way, often a paved or planted shoulder or a short setback on the sidewalk.9 Clear zones provide a run-off zone for errant vehicles that have deviated from the main roadway and are intended to decrease the frequency and severity of fixed-object roadside crashes, forgiving driver error.10
While clear zones are applicable as a safety parameter for the Interstate and freeway system, in urban settings, delineation of a minimum set back from the curb is not a required element. To the greatest extent possible, the lateral distance between the traveled way and the sidewalk (or parking lane) should be minimized, providing ample space for sidewalks and other amenities.11
Removal of roadside impediments (trees, street furniture, etc.) has an ambiguous safety record in urban environments and is at odds with city policies striving to increase pedestrian traffic and spur economic activity. Street trees and other roadside features are superior to wide shoulders or run-off zones, as they can decrease overall speeds and encourage a more pedestrian-friendly environment.
9 Clear Zones: Footnotes (NACTO Urban Street Design Guide)
10 Clear Zones: Footnotes (NACTO Urban Street Design Guide)
11 Clear Zones: Footnotes (NACTO Urban Street Design Guide)
