Estimates on the number of signs present on our roadways vary drastically. An NCHRP synthesis indicated 58 million signs, while a study for the FHWA estimated that there are approximately 250 million sign assemblies on the U. S. roadway system [15, 16]. Signs contribute an important role in increasing the safety of the roadway by providing regulatory, warning, control, and guidance information to the driver. Every sign that is installed on its own support system, however, provides a fixed object for a potential collision. Even a relatively small sign on an apparent weak support can have severe consequences when struck at high speed.
TABLE 7.1 Design Dynamic Deflections of Various Barrier Types
*Deflections are measured from the back of the post at the top.
MUTCD provides information on when traffic signs should be installed. In the case of regulatory signs, and in most cases for warning signs, there are specific warrants that should be met prior to installation . Installing unnecessary signs increases operating and maintenance costs, increases the potential of fixed-object collisions, and reduces sign credibility to the motorist.