Effect of Luminance on Information Acquisition Time and Accuracy from Traffic Signs

Objective:

Determine the effectiveness of signs with increased luminance by analyzing the relationship between luminance of a sign and the time it takes to acquire information from the sign, and the accuracy of the information that is acquired.

Problem:

Currently, there is little understanding of the quantifiable benefits of additional luminance over threshold legibility luminance provided by very-highly efficient retroreflective optics such as the full-cube optics for drivers within the functional legibility range. The question that this study aims to address is whether increasing the overall luminance of a sign is beneficial to the driver even when the sign is at or above the legibility luminance threshold. More specifically, the purpose of this research was to empirically test the hypotheses that (a) providing luminance above legibility threshold yields faster information acquisition and (b) when exposure is limited, brighter signs provide more accurate information transfer. The study determined the relationship between luminance (high and typical contrast levels, positive signs), exposure time, visual angle subtended by the text on the sign (or legibility index), and information transfer accuracy for a sample driver population over the age of 55 years.

METHOD:

An algorithm called “Up-Down-Transformed Rule” (UDTR) developed by Wetherill provides a simple yet methodical investigation protocol for forced-choice psychophysical responses, and therefore was used to collect the data in this study. UDTR is a method to converge on a desired level of performance by systematically increasing and decreasing an independent variable of interest based on the preceding responses.

Independent Variables:

Luminance of the sign.
Text size.
Percentile accuracy.

Summary:

The study suggests that the increased luminance of a sign reduces the amount of time that is required for one to acquire information. It was also found that the size of the sign increased a participants ability to acquire information more rapidly. The study has five key interpretations:

Higher sign luminance provides faster information acquisition thereby shorter time is required to reach a certain reading accuracy.
If the viewing time is limited, higher sign luminance and/or larger letter sizes provide more accurate sign reading.
Larger sign size has a very similar positive effect in legibility performance. Larger signs improve information transfer performance.
Information acquisition times are less affected by distance (or letter size) if the sign luminance is maintained at a high level.
Information transfer accuracy improves with increasing exposure time.

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