With increased traffic, multi-lane highways, and complex highway interchanges, highway signs play an important role in the safe operation of the nation’s transportation network. In the past, it was common to see a single large sign supported by a truss structure. In order to improve highway safety and operations, both static signs and dynamic message sign (DMS) must be used to communicate more frequently with drivers. These signs are typically larger and much heavier than the typical highway signs used in the past.

Given that wind is the main load that affects these structures during their lifetime, accurate calculation of the wind loads is essential. The existing specification needed to be updated to incorporate more current and accurate information on how the wind drag coefficient varies with (1) sign geometrical parameters (e.g., sign aspect ratio, ground clearance, and sign thickness), (2) shape of signs, and (3) type of supporting structures (e.g., signs are attached to a bridge superstructure vs. an overhead sign truss).

The objective of this research was to propose revisions to the wind drag coefficients in the AASHTO LRFD Specifications for Structural Supports for Highway Signs, Luminaires, and Traffic Signals (LRFDLTS-1). At a minimum, the research shall develop a methodology and design examples to calculate wind drag coefficients for signs and supporting structure members that are included in the LRFDLTS-1.

STATUS: The final deliverable has been published as NCHRP Research Report 1012. The research report can be downloaded here.