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Federal Highway Administration Research and Technology
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Publication Number: FHWA-RD-96-147
Date: October 1997
Development of Human Factors Guidelines for Advanced Traveler Information Systems and Commerical Vehicle Operations: Components of the Intelligent Transportation Systems: Designs Alternatives for In-Vehicle Information Displays
While the technical capability exists to display In–Vehicle Signing Information Systems (ISIS) and In–Vehicle Safety Advisory and Warning Systems (IVSAWS) information in a variety of ways, little human factors research exists to guide the selection of a preferred display design from among the range of potential design alternatives. Key human factors considerations associated with selecting Advanced Traveler Information Systems (ATIS) display alternatives include the accessibility, legibility, and understandability of ATIS information; the potential for ATIS information to facilitate driver decision–making; and the potential for ATIS information to distract the driver from the primary task of controlling the vehicle. A wide range of display design parameters are relevant to these human factors considerations as well. This experiment examines the effect of display modality, message style, and display location on driver compliance with warnings and driving safety. These design parameters must also be considered in the context of characteristics of the driving population (i.e., age and gender) and the environment (i.e., existing ATIS and road–sign infrastructure).
In this experiment, ATIS warning messages were presented to drivers using a low–fidelity automotive simulator equipped with an easily reconfigurable ATIS. The simulator is equipped so that ATIS messages can be presented visually, through liquid crystal display (LCD) panels, or auditorially through speakers. The visual scene can also be controlled to present drivers with roadway information in a form similar to the changeable–message signs found on many highways.
Driving safety and compliance with warning messages were estimated directly with several measures. In addition, several intervening variables were measured to provide a deeper understanding of the cognitive processes that mediate the effect of ATIS design characteristics on driver behavior, given particular driver and roadway characteristics.
A general issue facing ATIS designers is the concern that ATIS warning messages may go unheeded by drivers. A critical element of ATIS design concerns is to make information easily accessible and compelling so the drivers comply with the warnings. The results show converging evidence that ATIS warnings can generate a greater compliance compared to road signs; however, they may adversely affect trust and self–confidence. Certain ATIS designs may place drivers in a double–bind situation where they do not trust the ATIS, but they also feel that they cannot gather the required information themselves. This double bind may lead to dissatisfaction with the ATIS. The results also show that ATIS design characteristics can be manipulated to affect the level of driver compliance.
Another general issue that faces ATIS designers is its potential to undermine driving safety. Based on the information processing and mental workload paradigm, many have suggested that an improperly designed ATIS device could jeopardize driving safety by overloading drivers. Multiple–resource theory predicts this will be particularly critical for devices that force drivers to share their visual resource between reading ATIS warnings and the driving task. This investigation hypothesized another safety concern. An improperly designed ATIS device might jeopardize safety by leading drivers to favor in–vehicle information sources and ignore critical roadway information. The results of this experiment show that ATIS devices can undermine driver performance by fostering an overreliance on ATIS information. Their effects on workload, situational awareness, and driving safety measures all support this assertion. The results also show that ATIS design characteristics can exacerbate the overreliance and its negative effects on driving safety.
Not surprisingly, driver age emerged as an important variable that moderates the effectiveness of the ATIS. Although the overall driving performance of older drivers was worse than that of younger drivers, the presentation of ATIS messages had a less pronounced negative impact on safety for the older drivers than for the younger drivers. In addition, older drivers seem more likely to trust the capabilities of the ATIS, particularly when it is not entirely reliable.
Gender interacted with driver age and message style to influence the effectiveness of ATIS messages. Similar results for several dependent variables suggest that younger women assimilate ATIS notification messages more effectively than command messages. The opposite is true for older women, who assimilate command messages more effectively. For example, older women perceived less mental effort with command messages such as "Merge left," compared to younger women, who perceived less mental effort for notification messages such as "Accident ahead in right lane." In general, men assimilate notification messages more easily than command messages. These results show that complex sociological trends might complicate the design of ATIS devices.
An important design implication concerns the implementation of ATIS devices relative to the infrastructure of standard and changeable–message road signs. Providing drivers with only ATIS information leads to a high level of compliance, but it can also compromise safety. Providing ATIS information with redundant road–sign information generates a high level of compliance without the associated decline in safety.
Message style (command versus notification messages) emerged as a critical ATIS design characteristic, influencing both compliance and safety. Although message style has not been widely studied, results suggest that it has a more powerful effect on driver behavior than more commonly studied characteristics, such as display modality. Results of this study show that command messages promote greater compliance, but they reduce safety. Given the consequences for safety and compliance, command messages should be reserved for situations where an immediate and rapid response is required to preserve driver safety. This is particularly true for situations where redundant roadway information is not available.