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Federal Highway Administration Research and Technology
Coordinating, Developing, and Delivering Highway Transportation Innovations

 
REPORT
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Publication Number:  FHWA-HRT-16-061     Date:  November 2016
Publication Number: FHWA-HRT-16-061
Date: November 2016

 

Intersection Conflict Warning System Human Factors: Final Report

CHAPTER 5. DISCUSSION

In terms of sign comprehension, it did not seem to matter whether the “WHEN FLASHING” placard was present or not. Comprehension was similarly unaffected by whether the conflict warning was on a static yellow-diamond or on a dynamic blank-out sign. It was believed that blank-out signs would prevent drivers from misinterpreting non-flashing beacons (due to power failure) as the absence of conflicts. Present findings seem to contradict this belief; 73 percent of participants believed the blank blank-out signs meant that conflicting traffic was not present (see part 4 in chapter 4) despite being presented moments prior with a statement explaining that blank blank-out signs indicated a power failure.

A large subset of participants in this study did not comprehend the ICWS warning signs on the minor road approaches when the signs were placed to their left and right (directions where drivers must look to detect oncoming crossroad traffic). More than a few participants commented that those signs were facing in the wrong direction or “not for me.” A total of 77 percent of participants gave correct responses when asked what they would do in response to the minor road signs when those signs were directly ahead of them when stopped at the stop line. In this study, “directly ahead” was always on the far left corner of the intersection or on the left side of the median opening. It was assumed that placing the sign on the right corner, the right side of the median opening, or even overhead would be equally effective, but this assumption was not tested.

Participants overwhelmingly preferred signs with large letters, which was possible only on signs with short messages. In the laboratory, as in the real world, legibility was a function of font size. Although a number of participants preferred the syntactically more complete messages as their top choice, those same participants also identified the larger type signs as their next most preferred message. Overall, “CROSS TRAFFIC,” “EXPECT CROSS TRAFFIC,” and “CROSS TRAFFIC AHEAD” were preferred over all other ICWS message choices. All three of these messages fit on the diamond-shaped signs with the largest font used in this study. The larger font allowed a greater legibility distance and would also be expected to yield slightly shorter reading times, although reading time was not assessed in this study.

 

 

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