Field and Laboratory Studies of Warning Symbol Sign Legibility Distance
Frances A. Greene, Rodger J. Koppa, Ronald D. Zellner, R. Dale Huchingson, J.J. Congleton and A. Garcia-Diaz, Texas A&M University, March 1995, 156 pp.
Laboratory studies of warning symbol signs have been shown to underestimate legibility distances by up to a factor of two when compared with field studies. However, the research reported here suggests it may be more than just experimental settings contributing to disparity in research findings. For this research a new laboratory simulation technique was developed. The methodology optimized factors criticized in earlier studies, thus increasing fidelity. Correlation coefficients between laboratory and field legibility distances were very promising. The newly developed laboratory simulation was a successful first step at correcting problems associated with laboratory studies in the past. It is argued that recommended distances at which signs are to be placed, especially with consideration for older drivers, should be determined from a “worst-case” scenario of the minimum distance with tolerances.
Large within-subject variability, evident in both young and older driver age groups, overshadowed contributions of experimental variables. No studies have reported this finding of large within-subject variability in similar research. This variability led to an analysis of variation in distance estimation if different strategies for numbers of data points collected are used.
Keywords: Warning Signs, Legibility Distance, Older Drivers, Laboratory Study, Field Study, Within Subject Variability
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Reference Report #721917-1