Practices to Manage Traffic Sign Retroreflectivity (2012) / Chapter Skim
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Pages 6-13
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From page 6... ...
Assessment methods evaluate the retroreflectivity of individual signs and include visual nighttime inspection and measured sign retroreflectivity. Management methods incorporate an expected retroreflective life period of individual sheeting materials within the sign inventory.
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From page 7... ...
The overall type II error rate was 10.8% and the highest occurrence of this type of error was observed for yellow warning signs. Ultimately, the study acknowledged that visual nighttime inspection was a "reasonably accurate" method with "minimally trained personnel" (7)
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From page 8... ...
One or more of the following procedures can be used to support visual inspections: • Calibration Signs: An inspector views a calibration sign each time before conducting a nighttime field review. The calibration signs have known retroreflectivity levels at or above the specified minimums.
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From page 9... ...
Implementation of the expected sign life method can vary significantly; however, there are three main components to most successful systems. These components, in a hierarchical order, are establishing sign installation dates, identifying signs for replacement, and organizing sign data.
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From page 10... ...
– Computer-based systems are susceptible to technical problems and information loss. Blanket Replacement The blanket replacement method uses service life periods and is similar to the expected sign life method; the fundamental difference derives from targeting a large group of signs as opposed to identifying individual signs.
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From page 11... ...
Figure 2 is a map of a blanket replacement schedule and the divided areas. The blanket replacement method documentation is simple and an agency can draft a short policy memo justifying the service life period, defining the area boundaries, and outlining the yearly sign replacement procedures.
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From page 12... ...
rationalized that too little time between measurements of control signs may lead to the misuse of labor and resources, whereas long periods between readings may lead to inaccuracies in predicting service life in the field. This method not only indicates when corresponding signs in the field require replacement, but can also help to establish regional specific service life periods for different sheeting materials.
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From page 13... ...
It also showed that the sign direction and solar radiation variables were not acceptable predictors of inservice sign retroreflectivity. The researchers also created deterioration models for projecting service life periods in certain conditions.
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