Citation

Forbes TW, Gervais E, Allen T. Highw. Res. Board bull. 1960; 244: 16-29.

Copyright

(Copyright © 1960, National Research Council (U.S.A.), Highway Research Board)

DOI

unavailable

PMID

unavailable

Abstract

A need was indicated for improved signals for control of individual lanes on freeways and bridges in cases where accidents, maintenance, or unbalanced flow requires closing or reversing of a lane. Five criteria for more satisfactory signals than are now available for such use included (1) positive indication without false direction in malfunctioning, (2) distinctive appearance, (3) visibility and legibility, (4) ready understanding by most motorists, and (5) economic feasibility in the field. A series of different symbols was considered by the michigan highway department from which the red x and green-arrow-up were thought to fulfill qualifications 1, 2, 3, and 5, and to be most promising for qualification 4. To test the readiness of understandability by the majority of motorists, research was carried out in two parts. Part 1 was an engineering psychology approach, which measured the types of meaning most commonly associated with six different possible symbols. To reverse or clear a lane, the desired motorist interpretation would not be stop, but would be do not drive in this lane or move into another lane. A total of 253 graduate and undergraduate students viewed signal presentations by means of colored slides showing the signals as if in place on the mackinac bridge and gave a total of about 4,200 reactions to the critical signal. Part 1 was a laboratory study and part 2 a check of actual motorist reaction to the most effective signals when installed on the bridge. Three experiments in part 1 showed a consistent advantage for the red x as most often associated with the desired interpretation and least often with the undesired stop. This advantage was most marked in the first experiment, where some indication of possible meanings of the signals was given. The standard red bullseyes, on the other hand, showed consistently a lesser proportion of the desired response and the largest proportion of stop responses. The latter would be undesirable where a lane is being reversed or cleared in order to get tow trucks or ambulances to a broken-down vehicle or to an accident. The laboratory study, therefore, confirmed the hypothesis that for most motorists the red x possessed advantageous natural associations with the desired meanings. Part 2 consisted of checks of actual effects on bridge traffic of the red x and green-arrow-up. A simple experimental setup employed a light wooden barrier and red flag in the righthand lane beyond the signals. The red x was turned on for this lane during every alternate 5-min period. Comparisons of the point at which the weave was started showed that motorists were responding to the red x signal. Thus, the red x and green-arrow-up not only showed the advantage of natural association with a desired meaning as shown in the laboratory, but also produced the desired motorist reaction in actual traffic.