Ever since agencies started using uniform traffic signs, the conventional thinking concerning nighttime visibility is that brighter is better. But a recent Texas A&M Transportation Institute (TTI) research project revealed that signs along rural highways can be so bright that they cause disability glare to the point of reduced hazard detection distances, which can be a significant safety concern. (Read More)
Retroreflectivity
Raised question: TTI tests the durability of pavement markers
The worst of driving conditions calls for the best of roadway markers. With their reflective properties, retroreflective raised pavement markers (RRPMs) have guided many nervous drivers safely to their destination on rainy nights.
The durability and performance of RRPMs are critically important to departments of transportation nationwide. A few years ago, the Texas Department of Transportation (TxDOT) noticed an increased number of RRPM failures resulting from poor retention on pavements, physical damage and loss of retroreflectivity. In some cases, mass failures occurred when an entire section of RRPMs disappeared only weeks after installation. Read more
Guidelines for Nighttime Visibility of Overhead Guide Signs
A frequent dilemma facing highway agencies is deciding how to provide effective nighttime performance for overhead guide signs. While the Manual on Uniform Traffic Control Devices (MUTCD) provides minimum retroreflectivity standards for overhead guide signs, there are few guidelines that agencies can reference to decide how to provide sufficient nighttime performance of overhead guide signs in site-specific situations.
For instance, the common wisdom is that it is adequate to turn off overhead guide sign lighting in rural areas if highly reflective sheeting materials are used. However, there is little consensus about the use of lighting in suburban and urban areas where visual backgrounds and roadway geometries are more complex. Minimum sign retroreflectivity requirements are designed to provide conspicuity and legibility for all signs including overhead guide signs. In selected visual environments, such as urban areas with high visual complexity, higher levels of retroreflectivity or illumination or both may be needed to provide adequate conspicuity and legibility. (read more)