Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
HFG CHANGEABLE MESSAGE SIGNS Version 1.0 COMPOSING A MESSAGE TO MAXIMIZE COMPREHENSION Introduction Composing a CMS message to maximize comprehension refers to message formatting issues that affect driver understanding or reading times. Driver comprehension is important because the message may provide a legitimate safety warning that requires the driver to take an action. Drivers have a limited amount of time to comprehend the information and make a decision. Messages that are easy to comprehend reduce the amount of time required to read and grasp the meaning of the message, facilitate decision making, and promote faster responses. The following guidelines can be used to increase driver comprehension of signs. Design Guidelines Message Guidelines Property Abbreviations Avoid using abbreviations whenever possible. If abbreviations are necessary, use approved abbreviations from Section 1A.14 of the MUTCD. If the MUTCD does not include the desired abbreviation, create an abbreviation by removing letters from the end of a word until it is the desired length. Date/Day If the dates are in the next week: Format Use days of the week rather than calendar dates (e.g., "Tue Thur") Do not use "For 1 Week" because the start and end dates are ambiguous "Nite" may be used in place of "Night" A hyphen with a space on either side may be used in place of "Thru" "Weekend" may be used if the event begins on Saturday morning and ends on Sunday evening If the dates are not in the next week: Use a three-letter month abbreviation rather than a numerical month representation (i.e., "Apr 21" rather than "4/21") Only state the month once if both dates in a range are in the same month (i.e., "Apr 21 23" rather than "Apr 21 Apr 23") Don't include day, date, and time information Element Order Recommended precedence order for message elements is shown below. Note that only a limited number of elements should be included in a single message (adapted from Dudek (1)). Message Element Element Description 1. Incident/Roadwork/ Description of the unusual situation (use closure descriptor when all lanes on Closure Descriptor the roadway or ramp are closed) 2. Incident/Roadwork/ Location of the unusual situation Closure Location 3. Lanes Closed/Blocked Description of the exit ramps or lanes that are closed or blocked; can be used instead of Element 1 4. Effect on Travel Description of the severity of the situation to help the driver decide whether or not to divert (e.g., delay or travel time) 5. Audience for Action Used when the action applies to a subset rather than all drivers 6. Action Tells drivers what to do 7. Good Reason for Gives drivers confidence that following the action will improve safety or save Following the Action time Justification 1) Justify top row at left Use staircase indentation for 2) Center middle row rows: 3) Justify bottom row at right Message Provide specific diversion or incident location information when available. Specificity Use the phrase "This Exit" instead of the phrase "Next Exit" to refer to the upcoming exit. Based Primarily on Based Equally on Expert Judgment Based Primarily on Expert Judgment and Empirical Data Empirical Data 19-8
HFG CHANGEABLE MESSAGE SIGNS Version 1.0 Discussion Abbreviations: Abbreviations provide the benefit of reduced message length; however, their use is discouraged because they have been found to decrease message comprehension (2) and increase reading times (3). However, due to fixed sign size and message length recommendations, abbreviations can be necessary to convey the information to the level of specificity desired. Proffitt and Wade (3) report that in a study of sonar operators, viewers preferred truncated abbreviations over conventional (created by experts) or contraction (vowel removed) abbreviations. Truncated abbreviations proved to have faster response times and improved decoding times with subsequent trials. Date format: Research has shown that drivers have difficulty converting calendar dates to appropriate days of the week (1). However, it is often desirable to present closure or other information more than 1 week in advance, necessitating the inclusion of numeric date information in the message. In a laptop study examining date formats, Ullman, Ullman, and Dudek (9) found that regardless of the format that was used to present the day and date information, only approximately 75% of drivers could tell if the event would impact their current or future travel. Element order: The order of elements in a message varies widely depending on what information is known and appropriate to describe the incident. The MUTCD (4) states that on portable message signs, "if the message can be displayed in one phase, the top line should present the problem, the center line should present the location or distance ahead, and the bottom line should present the recommended driver action." This recommendation loosely maps to the recommended order of message elements by Dudek, included on the previous page (1). Justification: Greenhouse (2) found that staircase-justified messages increase reader comprehension, perhaps because this style better matches drivers' eye movements as they read the message. This recommendation contradicts the MUTCD standard that all text should be center justified (4). Message specificity: Message specificity is a message property that is affected by many different message aspects including space available on the sign, the information available to the Traffic Management Center, information unit limits, and message length limits. Wang, Collyer, and Yang (8) found through participant questionnaires that more specific messages (i.e., "Accident at Exit 12/Major Delays to Boston/Use Route I-295") are preferred to less specific messages (i.e., "Accident at Exit 12/Major Delays/Use Other Routes"). Pedic and Ezrakhovich (5) also report that drivers are more likely to correctly interpret a message when it includes a specific diversion task instead of a generic task. Drivers are also more willing to divert if given the incident location, expected delay, and best detour strategy rather than just a subset of that information (6). Survey data show that precise location information was preferred so drivers could make informed decisions about exiting/re-entering the roadway (7). When expressing exit information, "This Exit" instead of "Next Exit" was preferred to refer to the upcoming exit (7). Design Issues When used in messages, signal words (e.g., "Danger," "Warning," "Caution") may not be interpreted as intended and do not affect driver performance (3). Avoiding the use of such words can reduce reading time, conserve sign space, and prevent driver confusion. Sign comprehension also depends on driver literacy. Weak readers depend more on the message context for comprehension, are more affected by text degradation (similar to bulb burn-out on CMS), and hold more parts of a message in memory at a single time due in part to slower reading (3). Thus, Proffitt and Wade (3) recommend the use of context about the message subject, standardized message formats to enhance familiarity, and distinct directional statements. Because there is no literacy test required for driver licensing, message composition should accommodate varying reading competencies. Another aspect that affects comprehension is the use of symbols. Symbols can convey information without requiring driver literacy. In general, symbolic signs are recognized better, faster, and from further away than the corresponding text signs (3). However, care should be taken in their use because the meaning of symbolic signs is not always as well understood. Using a CMS to display television pictures of conditions or maps was not positively received by a majority of survey respondents (7). Cross References Driver Comprehension of Signs, 18-8 Presentation to Maximize Visibility and Legibility, 19-4 Presentation of Bilingual Information, 19-14 Key References 1. Dudek, C.L. (2004). Changeable Message Sign Operation and Messaging Handbook. (FHWA-OP-03-070). College Station: Texas Transportation Institute. 2. Greenhouse, D. (2007). Optimizing Comprehension of Changeable Message Signs (CMS). (UCB-ITS-PRR-2007-24). Berkeley: University of California Partners for Advanced Transit and Highways (PATH). 3. Proffitt, D.R., and Wade, M.M. (1998). Creating Effective Variable Message Signs: Human Factors Issues. (VTRC 98-CR31). Charlottesville: Virginia Transportation Research Council. 4. FHWA (2007). Manual on Uniform Traffic Control Devices for Streets and Highways . Washington, DC. 5. Pedic, F., and Ezrakhovich, A. (1999). A literature review: The content characteristics of effective VMS. Road & Transport Research, 8(2), 3-11. 6. Peeta, S., Ramos, J.L., and Pasupathy, R. (2000). Content of variable message signs and on-line driver behavior. Transportation Research Record, 1725, 102-108. 7. Benson, B.G. (1996). Motorist attitudes about content of variable-message signs. Transportation Research Record, 1550, 48-57. 8. Wang, J.-H., Collyer, C.E., and Yang, C.-M. (2005). Enhancing Motorist Understanding of Variable Message Signs. (FHWA-RIDOT-RTD-06-1). Providence: Rhode Island Department of Transportation. 9. Ullman, G.L., Ullman, B.R., and Dudek, C.L. (2007). Evaluation of alternative dates for advance notification on portable changeable message signs in work zones. Transportation Research Record, 2015, 36-40. 19-9
