Overhead guide sign retroreflectivity and illumination.
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Overhead guide sign retroreflectivity and illumination.

Filetype[PDF-1.89 MB]

  • English

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    • Abstract:
      Roadway guide sign visibility during darkness is fundamental to driver safety, especially elderly drivers. Guide

      sign visibility can be improved by external sign illumination or the use of retroreflective sheeting on signs. Because

      energy conservation is essential in the midst of a worldwide energy crisis, various Departments of Transportation have

      investigated usage of energy-efficient lighting technology with overhead guide signs.

      This report presents results of a survey related to overhead sign lighting usability by states, a laboratory

      experiment to compare the light distribution of five light sources used to illuminate overhead guide sign by several

      states, a cost analysis for the tested light sources, a field experiment to compare the visibility of three retroreflective

      sheeting used by states, a cost analysis for the tested retroreflective guide signs, and an analysis by determining the

      most cost-effective method of increasing overhead guide sign visibility to drivers during nighttime.

      A laboratory experiment was conducted to compare the light distribution of three conventional light sources:

      Metal Halide, Mercury Vapor, and High Pressure Sodium, and two new generation light sources: Induction lighting,

      and Light Emitting Diode. Combining two decision criteria, the light distribution and the cost, resulted in finding the

      Induction lighting to be the recommended light source for those states that want to continue illuminating their

      overhead guide signs. A field experiment was conducted to compare three types of sign sheeting, Engineering Grade

      (type I), Diamond Grade (type XI), and High Intensity (type IV), in order to determine the sign sheeting material that

      best improves sign visibility. Combining the decision criteria to compare these three retroreflective sheeting, the

      visibility and the cost, High Intensity (type IV) is the recommended sign to be used by DOTs, followed by Diamond

      Grade (type XI).

      In comparing the best options used to increase sign’s visibility, sign illumination and sign retroreflectivity, it is

      found that using retroreflective sheeting is more cost effective than sign illuminating.

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