Can Traffic Signs be Too Bright on Low-Volume Roads?

The objective of this study was to investigate the concern that signs along rural highways can be so bright that they cause reduced legibility or glare, or both, to the point of their being a safety hazard. The researchers recruited participants and conducted visibility studies on a closed-course facility to assess how various levels of brightness of speed limit signs can affect nighttime participants' ability to read the signs and detect various types of potentially hazardous objects along the edge of the traveled way. From the findings, considerations are provided for low-volume rural highways with average daily traffic of 5,000 vehicles per day or less. To avoid glare and reduced object detection distances, ASTM Type III or IV materials should be specified for regulatory and nonfluorescent warning signs on these low-volume roads. Also, because of reduced object detection distances, recommendations are made to avoid the installation of unnecessary signs. Not only do unnecessary signs provide a potential hazard for errant vehicles, but they also add to the overall maintenance responsibility, breed disrespect for traffic signs, and reduce the visibility of potentially hazardous objects along the roadside.