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HFG SIGNING Version 1.0 DRIVER COMPREHENSION OF SIGNS Introduction Sign comprehension refers to a driver's or road user's ability to interpret the meaning of a sign. Signs should be designed and presented so that their message is comprehended and understood by users. As discussed in Campbell, Richman, Carney, and Lee (1), in the context of icons and symbols, there are three stages associated with the comprehension and use of signs: legibility, recognition, and interpretation. Legibility reflects the relationships among the driver, the sign, and the environment; it is essential for the initial perception of the sign and includes parameters such as luminance uniformity, contrast, and size. Recognition reflects whether or not the driver can readily distinguish the sign, especially in the context of other signs and stimuli. Interpretation reflects the relationships among the driver, the sign, and the referent or message associated with the sign; it includes parameters such as whether the driver comprehends the meaning, intent, or purpose of the sign. This guideline identifies message format recommendations for improving drivers' comprehension of road signs. As shown below, information can be presented in a text-only, graphic/icon-only, or mixed textgraphic format. Design Guidelines The following guidelines provide parameters for the use of text-only, graphic/icon-only, or mixed textgraphic formats. Format Example Guidelines Use for highly complex messages. Use when indicating hazards. Text Only Use for destination information. Use in areas requiring unexpected or unique driver actions, e.g., frequent lane shifts. Use for safety and warning information. Use for prohibited actions. Use in visually degraded conditions. Graphic / Icon Only Use in areas with higher posted speeds. Use diagrammatic graphics when road geometry violates driver expectancies. Minimize symbol complexity by using few details. Add text when symbols alone are unintuitive. Keep text to no more than two to three words. Mixed Use a clear and simple font for the text. Based Primarily on Based Equally on Expert Judgment Based Primarily on Expert Judgment and Empirical Data Empirical Data 18-8

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HFG SIGNING Version 1.0 Discussion The figure below shows the three stages that appear to be associated with comprehension and use of signs: legibility, recognition, and interpretation. As shown below, this sequence of icon comprehension refers to the perceptual and cognitive process by which users interpret the meaning of a sign. Legibility Recognition Interpretation Can the driver see the sign? How well do the parts of this sign How well does the sign convey the Is it legible at various distances? relate to one another? message? Can it be seen under both nighttime Does the construction of the sign Will it be understood when presented in the and daytime lighting conditions? support accurate recognition? appropriate context? Is it easily confused with other signs? Does it require special knowledge particular to a culture, language, or driver age? Source: adapted from Campbell et al. (1) The format of a sign--i.e., text only, graphic/icon only, or mixed--should be selected to maximize information transmission and comprehension, given the nature of both the sign's message and the general roadway environment. Text-based signs are clearly more appropriate for highly complex messages, such as destination messages or hazard warnings that are more quickly and easily presented via text. It has long been recognized that well-designed icons are generally recognized more accurately and quickly than text-based signs meant to convey the same message (2) and that icons can be presented in a much more spatially condensed form (3, 4, 5) than can most text-based messages. Road signs also have a limited amount of space for presenting information and must take advantage of the ability of icons to present more information to the driver than can be presented textually. Research in this domain has shown that icons can be recognized more rapidly and are legible at greater distances than information presented in other formats (6, 7). The absolute numerical differences in mean reaction times are not relevant because of the differences between the task performed in the study and the actual driving task. Design Issues Comprehension tests are evaluation techniques that provide a means to determine whether a candidate sign for a roadway message is likely to be properly understood by typical roadway users. Overall, a rigorous and iterative evaluation process will increase the likelihood that the implementation of the sign on the roadway will improve overall traffic safety, and not detract from it. A number of procedures can be used to measure driver comprehension of signs, including the recently released J2830, Process for Comprehension Testing of In-Vehicle Icons, an SAE Information Report within the SAE Standards series. Also, road engineers may consider message format based on location and driver demographics. For example, non- native-English speakers can correctly interpret graphic messages without relying on their knowledge of the English language. An increased use of transportation graphic signs in the vicinity of non-native-English-speaking population areas may be appropriate. Cross References Presentation to Maximize Visibility and Legibility, 19-4 Key References 1. Campbell, J.L., Richman, J.B., Carney, C., and Lee, J.D. (2004). In-Vehicle Display Icons and Other Information Elements. Volume I: Guidelines (FHWA-RD-03-065). McLean, VA: FHWA (http://www.tfhrc.gov/safety/pubs/03065/index.htm). 2. Edworthy, J., and Adams, A. (1996). Warning Design: A Research Prospective. Bristol, PA: Taylor & Francis. 3. Zwaga, H.J., and Boersema, T. (1983). Evaluation of a set of graphic symbols. Applied Ergonomics, 14, 43-54. 4. Rohr, G., and Keppel, E. (1984). Iconic Interfaces: Where to Use and How to Construct Human Factors in Organisational Design and Management. The Netherlands: North-Holland. 5. Hemenway, K. (1982). Psychological issues in the use of icons in command menus. Proceedings of the CHI 1982 Conference on Human Factors in Computer Science (pp. 20-23). New York: Association for Computing Machinery. 6. Ells, J.G., and Dewar, R.E. (1979). Rapid comprehension of verbal and symbolic traffic sign messages. Human Factors, 21, 161-168. 7. Jacobs, R.J., Johnston, A.W., and Cole, B.L. (1975). The visibility of alphabetic and symbolic traffic signs. Australian Road Research, 5(7), 68-86. 18-9