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Federal Highway Administration Research and Technology
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Publication Number: FHWA-RD-95-197
Date: December 1996
Development of Human Factors Guidelines for Advanced Traveler Information Systems and Commercial Vehicle Operations: Comparable Systems Analysis
Modification of Human Factors Guidelines: Fitting the System to the Constraints
Early design concepts visualized a display screen and controls tailored to the characteristics of the information to be displayed and actions to be input by the driver. However, since TravTek was to be a limited edition system for operational fieldtest purposes and not a mass–produced production system, economic considerations dictated that an existing display and touchscreen system already integrated into the vehicle instrument panel be used as the major driver interface. The 1992 Oldsmobile Toronado included such a system as an option and was therefore selected as the vehicle for the operational field test (Carpenter et al., 1991).
While human factors were considered relatively early in the conceptual design process, there were already a number of system and user constraints. The TravTek functions make use of a color CRT with hard keys and touchscreen controls located in the dashboard section of the car usually reserved for the radio. The TravTek system shares the "vehicle information center" with the radio, climate controls, vehicle status indicators, and Yellow Pages Directory. So the CRT placement and screen size, the color palette, and the number and spacing of soft key controls were fixed. A set of hard keys located on the steering wheel were made available, and an auditory message system was added to augment the visual display. Due to the number and variety of messages to be presented by the system, it became necessary to use synthesized, rather than digitized, natural voice.
Display of map information, and especially of route guidance information, constituted the biggest design challenge. Most prior research points out what not to do, rather than what to do, for map displays. For the driving mode, it is important to reduce the density and distraction quotient to minimize eyes–away–from–the–road time. Because of character size and the touchscreen characteristics, labels on the soft keys could contain no more than two rows of four characters each, and menu items also had space restrictions. A series of studies identified labels that were understandable to untrained users, given the size constraints. Multiple ways of displaying traffic information visually were investigated to arrive at a set of symbols that were clear and did not conflict with each other (Carpenter et al., 1991).
Although there is no consensus on the use of maps and touchscreens while driving, the TravTek philosophy was to proceed with caution. This conservative approach led to the distinction between functions available to the driver only in a pre–drive mode (while the car is in PARK) and functions available while driving.
In addition, to reduce the necessity for the driver to look at the display screen while driving, auditory displays using coded tones and synthesized voice messages were added to the design to supplement the visual information. The decision was made early in the design process to eliminate the use of touchscreen keys while the car is in motion, and to allow the driver to make system inputs only through activation of steering wheel buttons while driving.
Constraints Imposed by the User Population
TravTek users were mostly rental car customers, although there were also some local residents. The age range of these drivers was approximately 25 to 65 years old. Their level of education varied from high school to college with limited computer experience to highly experienced computer users. The opportunity for training was minimal. Therefore, in addition to constraints imposed by a multi–task environment, special emphasis had to be given to making the system as easy to use as possible.