DRIVER-HEADLAMP DIMENSIONS, DRIVER CHARACTERISTICS, AND VEHICLE AND ENVIRONMENTAL FACTORS IN RETROREFLECTIVE TARGET VISIBILITY CALCULATIONS

The inputs that are necessary for comprehensive visibility models are discussed. Inputs required by visibility models may deal with the physical arrangement of the observer and headlamps in three-dimensional space, the headlamp characteristics in terms of candlepower output and efficiency, observer age, observation time, probability of detection, and minimum preview time. There are also a number of environmental and vehicular parameters such as horizon sky luminance, atmospheric transmissivity, and windshield transmission. One problem associated with using comprehensive visibility models is the lack of standards, guidelines, and recommendations for the required model inputs. Consequently, it is currently difficult or even impossible to duplicate visibility model runs reported by others. Standardized headlamp-observer-target scenarios, standardized observer characteristics, and standardized environmental parameters would greatly facilitate cross-validation of model outputs. Numerous model input dimensions and values that are based on the technical literature are provided here. However, because there are no comprehensive eye location percentile dimensions available for late-model automobiles and for recent anthropometric dimensions, an exploratory vehicle survey was conducted and the measured vehicular dimensions were combined with anthropometric dimensions extracted from the 1988 U.S. Army personnel survey. The result of this effort is a table that shows the driver eye locations as a function of the population percentile, observer gender, and vehicle class. Further results include data pertaining to the location of low-beam headlamps. The recommended model input values should be considered for adoption as a standard that would facilitate easier cross-validation of visibility model results