A two-phase study on the design and display factors of changeable message signs (CMSs) was conducted through a series of blocked-factorial experiments. Subjects sit in the driver's seat of a 1998 Ford Taurus sedan. Computers generated CMS images, merged with a driver's view driving video, and were projected onto a screen in front of the vehicle. Subjects were required to make proper responses signaling their comprehension of the CMS stimuli. Eighteen subjects balanced by age and gender participated the experiments. Phase I investigated the effects of discrete displayed CMSs' font size, font color, subjects' age, gender, and their interactions. It found that font color, drivers' age, and gender significantly affected response time. Green and 5 7 matrix were the best font color and font size respectively. Older drivers responded the fastest among the three age groups but with the lowest accuracy. No significant correlations were found between response time and accuracy. Response times of different subjects were significantly different, but the effects of font color and size were consistent. Phase II studied the influences of display format, number of message lines, lighting, driving lane, and their interactions. It found that discrete displayed messages took less response time than sequential displayed ones. Single-line messages were better than multiple-line ones. Motorists could better view CMSs in sunny days, and better view CMSs when driving in the outer lane. Older drivers exhibited slower response and less accuracy than younger drivers; females exhibited slower response but higher accuracy than males.
Abstract