In this paper, TTI researchers summarize the results of daytime and nighttime legibility distance studies of amber variable message signs (VMSs) utilizing aluminum indium gallium phosphide (AlInGaP) LEDs with 457mm high characters. Researchers performed proving ground studies under multiple sun position (daytime) and lighting (nighttime) conditions, and validated these studies with limited field testing in Texas and New Jersey. Three different driver age categories were examined: less than 45 years old, 60-74 years old, and greater than 75 years old. As expected, study results indicate significant differences in LED VMS legibility distance by age category. However, legibility distances were only slightly affected by sun position (sun above sign, sun shining directly on sign face [washout], sun behind sign [backlit]) or by nighttime lighting condition around the VMS (no external lighting, oncoming headlight glare, overhead lighting). Furthermore, these distances exceeded those measured in previous studies in which older LED VMS technology was utilized. (A*)
Abstract