NCDOT assessment of automated sign retroreflectivity measurement : final report.
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2016-06-27
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Alternative Title:Assessment of automated sign retroreflectivity measurement.
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Edition:Final report, August 2013 to June 2016
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Abstract:The Institute for Transportation Research and Education at North Carolina State University conducted a follow-up study to
a previous North Carolina Department of Transportation (NCDOT) project, comparing mobile inventory data collection
vehicles to manually-collected data techniques. In the previous studies, sign retroreflectivity readings were either
captured with low degrees of accuracy or not captured at all. The follow-up study focused mainly on automated sign
retroreflectivity capture, but also looked at vendor capabilities regarding other sign features. The results show that
vendors can accurately locate the majority of signs. However, while vendors were unable to consistently capture sign
retroreflectivity readings within 10% accuracy, a comparison of MUTCD pass/fail ratings for signs for these vendors
showed that they captured ground-mounted signs with 88% and 97% accuracy, and overhead signs with 100% accuracy.
Combining the sign location rates and the accuracy of the pass/fail comparison results in an overall accuracy ranging from
63% to 70% which is comparable to the accuracy achieved by other sign management methods. Vendors also showed
some consistency in capturing the lower retroreflectivity readings, which should be more important to the NCDOT, as
MUTCD thresholds for failing signs are set at the lower level readings. Following location of the sign, vendors showed
promise collecting many of the other sign features, such as MUTCD code and roadside orientation, which showed
significant improvement from the previous study. This study shows that there is still room for improvement, but also
exhibits the improvements that vendors have already made in capturing all sign features.
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