## 4 Advanced In-Vehicle Displays
### NHTSA Guidelines for In-Vehicle Messaging  
NHTSA developed a series of design guidelines for driver vehicle interfaces including those for presenting information during manual driving [7]. The current guidelines state that messaging content needs to be designed to pose minimal additional workload and not obstruct a driver's capability to process information from the roadway [7]. As processing information from an in-vehicle display may demand the same pool of perceptual and cognitive resources a driver needs to operate the vehicle, poor interface design could lead to distracted driving [63]. In specific, NHTSA recommendations state that displays should support tasks that can be completed with sequential glances that are brief enough not to affect driving and tasks that do not require the driver to make time sensitive responses [7]. These guidelines are supported by previous work that has empirically investigated driver distraction (for a comprehensive review see [64]). During manual driving, effective messaging content needs to be informative without increasing workload, but these needs may become more complex in automated driving, given the general underload issue, and sudden unexpected spike of workload in the event of an automation takeover.  
The design of in-vehicle messaging for automated driving needs to consider the three phases of driver display information processing, including: extraction, recognition, and interpretation [62]. Extraction relates to how easily the message can be perceived by the driver; recognition refers to the structure of the message and whether it accurately represents the information it is trying to convey to the driver; and interpretation depends on the capability of the driver to understand the message [7]. While these phases have been considered in manual driving systems design, they may also apply to automated driving, with the additional factor that drivers will likely disengage from the driving task. For example, NHTSA released guidelines for how the elements in a visual display should be presented to optimize the three phases of message presentation and processing. Specifically, the use of certain representations can aid in driver processing of information. One example is the use of displays that present the criticality of warnings in terms of scaled distance to a crash point. Another example is the use of symbolic or pictorial information to aid understanding without the need to read text [7]. NHTSA also recommends symbolic or iconic images to give meaning to analog displays, such as a collision warning, so that drivers do not need to read for interpretation. Spatial information can be used to represent intersection configurations and lane locations. Representational information can be used when specific locations or destinations need be conveyed to the driver, such as a merge lane position [7]. The use of stimulus-response compatibility, or consistency between the type of display and type of information being displayed, allows these specific representations to aid driver understanding of information and the effectiveness of such design elements has been supported empirically [7; 65; 66].  
Another issue is the amount of data being presented in a display, which can result in display clutter. Research has indicated that the amount of attention devoted to a display increases with an increasing amount of clutter [67]. [PERSON] and [PERSON] extended these findings and observed that in higher workload situations, drivers exhibit shorter glances to displays to account for increased clutter [68]. This behavior occurs despite drivers allocating insufficient time (with short glances) to process information. Altogether, these findings suggest that the design of in-vehicle messaging needs to pay careful attention to driver workload, the ability of the drivers to process information, and limiting display clutter to assist the driver in perceiving necessary information.