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OCR for page 26
HFG SIGNING Version 1.0 GENERAL PRINCIPLES FOR SIGN LEGENDS Introduction Sign legends refer to the text and/or symbols composing the sign message. Legends that are too long or too complicated can lead to problems in comprehension. In general, the legend on a sign must be kept to a minimum, regardless of letter size, to maximize driver comprehension. Design Guidelines Example Type of Sign Guidelines (all from MUTCD (1)) Advance Guide Limit route and destination information to a total of three lines Do not use more than two destination/street names. Place intersecting streets on top line and distance to intersecting streets on bottom. Conventional Limit route and destination information to a total of three Guide lines. Exit Direction Limit route and destination information to a total of three lines. Do not include more than two destination/street names. Tourist Place symbols to the left of the word legend. Limit information to a total of two lines. Service Limit general road user services to six. Distance Limit traffic generators to three accompanied by the related distance. Keep the highest priority distance (nearest distance) at the top or left. Lane Control Place the legend at the top of the sign. Based Primarily on Based Equally on Expert Judgment Based Primarily on Expert Judgment and Empirical Data Empirical Data 18-2

OCR for page 26
HFG SIGNING Version 1.0 Discussion The relatively small amount of available space on roadway signs suggests the need to make the best use of this space when designing legends. The guidelines on the previous page have been adapted from the MUTCD (1) because of their common focus on legends and because they are provided across various sections/pages within the MUTCD and can be hard to find. In general, they reflect acceptable, best practices for sign legends. The legend for a sign should be selected to maximize information transmission and comprehension, given both the nature of the sign's message and general roadway environment. Text-based signs are clearly more appropriate than symbolic signs for highly complex messages, such as destination messages or hazards that are more quickly and easily presented via text rather than potentially ambiguous or unfamiliar symbols. There is a trade-off between the amount of information provided in a sign, the complexity of the sign information, and its overall comprehensibility. Either through the use of more words or through the use of complex graphics, the density of information presented on a sign can be increased, but often at the cost of legibility and/or comprehensibility. New sign designs (or even existing signs being used in a new location or a new way) should always be tested, using a representative group of drivers, to see if they support adequate levels of driver comprehension. Design Issues Sign placement and appropriate letter height are determined by a number of factors. A process for determining these values is presented in the Traffic Control Devices Handbook (2) and discussed in more detail in Tutorial 5. Appropriate sign placement is determined by the overall information presentation distance, which is the total distance at which the driver needs information about the choice point (e.g., intersection). This distance is the sum of the reading distance, the decision distance, and the maneuver distance. The reading distance is determined by the amount of time that the driver needs to read the sign's message, depending on the number of words, numbers, and symbols contained in the message. The decision distance is determined by the amount of time needed to make a choice decision and initiate a maneuver. The decision time necessary depends on the complexity of the maneuver. The maneuver distance is determined by the time necessary to complete any maneuver required by the choice. For a lane change maneuver, this distance is the sum of the gap search, lane change, and deceleration distances. These values are all influenced by the vehicle operating speed. Once the reading, decision, and maneuver distances are summed to find the information presentation distance, the advance placement distance between the sign and the choice point can be subtracted to find the legibility distance, which is the distance at which the sign must be legible. The required letter height can be calculated by referencing the legibility index provided in the MUTCD (30 ft/in.). When the legibility distance is divided by the legibility index, the letter height is obtained. Information Presentation Distance Reading Decision Maneuver Distance Distance Distance Gap Search Lane Change Deceleration Legibility Distance Advance Placement Cross References Presentation to Maximize Visibility and Legibility, 19-4 Sight Distance Guidelines, 5-1 Key References 1. FHWA (2007). Manual on Uniform Traffic Control Devices for Streets and Highways. Washington, DC. 2. Pline, J.L. (Ed.). (2001). Traffic Control Devices Handbook. Washington, DC: ITE. 18-3