Spacing Chevrons on Horizontal Curves

Abstract

The chevron alignment sign is an important traffic control device used to warn drivers of the severity of a curve by delineating the alignment of the road around that curve. FHWA's Manual on Uniform Traffic Control Devices for Streets and Highways provides the following guidance on the spacing of chevrons around a curve: “The Chevron Alignment sign should be spaced such that the road user always has at least two in view, until the change in alignment eliminates the need for the signs” and “the Chevrons should be visible for a sufficient distance to provide the road user with adequate time to react to the change in alignment.” This guidance is broad to account for geometric design features and site obstructions such as steep vertical curvature or heavy vegetation. It also allows flexibility based on site characteristics and available funds, and the use of this verbiage creates a lower liability risk than there would be if a spacing chart were used. However, the broad wording allows for inconsistencies in the roadway system and provides little guidance for maintenance personnel. A field study was conducted to investigate the impacts of varying the number of chevrons in view around a curve. A spacing chart was then developed to simplify maintenance personnel's responsibility for choosing appropriate chevron spacing. The results of the field study indicated that having more than two chevrons in view around the curve provided a benefit in the form of a reduction in speed of about 3 mph at night. Smaller speed reductions were observed during daylight.