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Transportation research synthesis : effectiveness of traffic signs on local roads.
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2010-01-01
[PDF-104.47 KB]
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Alternative Title:Effectiveness of traffic signs on local roads
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Abstract:There does not appear to be significant credible research demonstrating the outright ineffectiveness of particular
traffic warning signs. The research we identified provides support for opposing points of view: that traffic warning
signs have a minimal or neutral effect on safety, or, alternatively, that warning signs are effective at reducing crash rates and severity. National guidance recommends that traffic warning signs be employed based on engineering
studies and engineering judgment, and suggests that the excessive use of signs can reduce their effectiveness.
The MUTCD guidance on warning signs begins with the direction that “the use of warning signs shall be based on an engineering study or on engineering judgment.” It further indicates that “the use of warning signs should be kept
to a minimum as the unnecessary use of warning signs tends to breed disrespect for all signs.” That directive is not
followed by guidance or research indicating what types of signs are actually ineffective.
Traffic sign effectiveness appears to be more a matter of perception and opinion than of fact based on evidence. For
example, NCHRP Synthesis 186, Supplemental Advance Warning Devices (1993, page 1), found that “the majority of the devices encountered in this project were not evaluated by formal effectiveness studies, but are simply
perceived to be effective by the responding agency.” A study of the effectiveness of static warning signs by the
Institute of Transportation Engineers (“Static Warning Signs of Occasional Hazards: Do They Work?”) came to a
similar conclusion. In that study 18 percent of responding state transportation agencies thought the use of static warning signs for occasional hazards was effective, but 93 percent indicated that no studies had been done to
investigate the actual effectiveness of the signs.
On the other hand, Fred Ranck, FHWA safety and design engineer, indicated in an interview that warning signs have
proven safety benefits (see the National Research and Guidelines section on page 3).
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