Legibility of freeway Lane Control Signals

Abstract

This thesis documents the results of a laboratory study designed to evaluate and compare the glance legibility distance of commercially available freeway Lane Control Signals (LCS). Two prototype fiber-optic lane control signals were evaluated to determine their suitability for freeway-lane-control-signing applications. The LCS used in the study were obtained from C.J. Hood, Inc., and Electro Fiberoptics, Inc. This study emphasized the visibility of the standard LCS displays (their ability to be detected and recognized) rather than their comprehension (their ability to be understood by a majority of the drivers). For this, glance legibility distance was used as a Measure of Effectiveness (MOE). It is the distance at which the sign catches the attention of a driver in a limited time of exposure. The glance legibility was evaluated and compared for the corresponding symbols displayed by the two signs. An attempt was made to correlate the difference in legibility to the differences in sign design characteristics. Also evaluated was the sensitivity of glance legibility to the gender and age of the subject. The glance legibility distances of the symbols displayed by the two signals were analyzed for their compliance with the MUTCD guidelines. Glance legibility of "Red X", "Yellow X", and "Green Arrow" displayed by the two signs was found to be in the ranges of 750-950 feet, 800-1000 feet, and 1200-1400 feet respectively. The size of the sign, brightness of the display, and the pixel arrangement were found to be the main design characteristics that have a direct bearing on the legibility of the displays. Brightness of the sign is a greater determinant than the color of the display. Significant differences exist between the color versus symbol recognition distances. The signal displays were visible but not legible. The glance legibility does not depend upon the gender of the driver; however, significant differences in legibility of displays were found to exist between the younger and the older age groups. The results of this study will lead to a better understanding and utilization of LCS systems and will promote more uniformity in the design, installation, and operation of LCS systems in the most cost effective manner possible; however, further research needs to be done as regards the factors contributing to the effective visibility of freeway LCS . In summary, there is a need to make an in-depth study of the interrelationships between the LCS hardware elements (e.g. the light intensities, symbol displays, color combinations etc), geometric features and traffic conditions, mounting characteristics, and driver limitations so as to promote more uniformity in the application of LCS to freeway traffic management.