Overhead guide sign retroreflectivity and illumination.

PDFTech ReportK-TRAN: KSU-11-6C1889Overhead traffic signsRetroreflectivityVisibilityEnergy conservationCostsLightingSurveysState departments of transportationField testsLaboratory testsRecommendationsKansasKansas. Dept. of TransportationObeidat, MohammedRys, MalgorzataRussell, Eugene R.Kansas State University. Transportation CenterUS Transportation CollectionRoadway guide sign visibility during darkness is fundamental to driver safety, especially elderly drivers. Guidesign visibility can be improved by external sign illumination or the use of retroreflective sheeting on signs. Becauseenergy conservation is essential in the midst of a worldwide energy crisis, various Departments of Transportation haveinvestigated 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 laboratoryexperiment to compare the light distribution of five light sources used to illuminate overhead guide sign by severalstates, a cost analysis for the tested light sources, a field experiment to compare the visibility of three retroreflectivesheeting used by states, a cost analysis for the tested retroreflective guide signs, and an analysis by determining themost 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 theInduction lighting to be the recommended light source for those states that want to continue illuminating theiroverhead 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 thatbest improves sign visibility. Combining the decision criteria to compare these three retroreflective sheeting, thevisibility and the cost, High Intensity (type IV) is the recommended sign to be used by DOTs, followed by DiamondGrade (type XI).In comparing the best options used to increase sign\ue2\u20ac\u2122s visibility, sign illumination and sign retroreflectivity, it isfound that using retroreflective sheeting is more cost effective than sign illuminating