The National Academies

NCHRP 15-67 [Completed]

Wind Drag Coefficients for Highway Signs and Support Structures

  Project Data
Funds: $300,000
Research Agency: University of Iowa
Principal Investigator: Dr. George Constantinescu
Effective Date: 11/7/2018
Completion Date: 12/31/2021
Comments: To be published as NCHRP Report 1012

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.

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