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11 LED-Based Lamps it did not provide final answers on the relevance of these factors to particular applications. Many systems that use yellow LEDs as a light source are now available. A few are based on the 360 flashing-light assembly, but many are strictly for directional purposes. It is likely that Identification of Relevant Factors more of these assemblies will replace the 360 or rotating Based on the results of the literature review, a prioritiza- assembly in the future because of the electric efficiency. tion of the relevant factors was conducted by surveying knowl- edgeable practitioners. As an initial evaluation, the factors Literature Review Conclusions were characterized as lighting factors, vehicle factors, environ- Because the presence of maintenance vehicles on the road is mental factors, and driver factors. Of these factors, only light- an uncommon event with low probability, motorists consider ing and the vehicle factors are controllable by the responsible their encounters with maintenance vehicles to be unexpected agency. events. Any measure that increases the distance at which mo- Through the survey, the lighting factors were found to be torists are informed about the presence of maintenance vehi- most critical, followed by the environmental and driver fac- cles will increase the time available to react. Because signs are tors. The vehicle factors were not regarded as important as stationary countermeasures and the operation of shadow the others. vehicles is expensive, the use of more conspicuous warning Based on these findings, an experimental program was de- lights is desired. veloped that included an initial screening experiment to reduce The literature review provided guidance on which factors the number of lighting factors to be considered followed by a (e.g., light color, types of lights, ambient lighting, lighting in- dynamic experiment in which the weather conditions could tensity, driver factors, the use of flashing, etc.) should be con- be investigated. sidered in developing guidelines for the use of warning lights A complete description of the relevant factors and the knowl- and therefore should be considered in this research. However, edgeable practitioner survey is provided in Appendix B.