## 5 Factors That Influence the Effectiveness of In-Vehicle Messaging
### Driver Characteristics
#### 5.1.1 Cognitive Capabilities and Messaging Display Design  
Drivers' cognitive capabilities in attention and working memory have been shown to be significant predictors of driving performance and safety [85; 86]. In specific, spatial attention has been identified as being a strong predictor vehicle and traffic awareness. Spatial attention refers to the allocation of attention to locations in the visual field [87]. Spatial attention is affected by peripheral and central cues, which involve reflexive orienting and volitional orienting, respectively [88; 89]. During driving, an individual must direct their attention to several different locations in the vehicle to develop a complete \"picture\" of vehicle status. This process is related to automated driving because the driver may be required to reallocate attention from a secondary task to a display in the car during a takeover request. The design of in-vehicle displays should support this shift of attention. For example, auditory cues have shown promise for capturing and diverting attention to visual information that is spatially coupled with the auditory cue [90]. Therefore, any messages presented at an in-vehicle visual display will benefit from a pairing of auditory information to best alert the driver to the information.  
Another related consideration is individual differences in spatial attention [91; 92; 93; 94]. To effectively design messaging content, individual attentional capability must be considered, as messaging may fail to enter a driver's state of awareness or unnecessarily capture too much attention. These factors are especially important for older drivers who may need accommodations due to reduced attention capability with age-related changes. Design practices, such as decreasing visual clutter, providing multi-modal messaging, as well as using advanced cues (such as an early notification of upcoming signage) to reduce simultaneous competition of attention could all be considered.  
Driver working memory is also a critical cognitive factor, as driving is a complex task that demands storing and manipulation of information in real-time [95]. Research has shown that high working memory capacity novice drivers were less affected by increasing cognitive load in a driving task. They performed better in lane changes, identified developing hazards in video clips more quickly by using more efficient eye movements in a dual-task condition, and were less likely to experience instances of inattention during driving [96].  
Taken together, the above results suggest that lower-cognitive capacity individuals perform worse on hazard perception performance partially because they fixate less on the hazard, which greatly reduces their ability to identify, interpret, and respond quickly to the hazard [95]. These observations lead to the inference that in-vehicle messaging should consider a driver's working memory as it varies among individuals and throughout the life span. While automated driving does not require a driver to be actively engaged in the task of driving, the need for the driver to be ready to takeover vehicle control can result in drastic changes in cognitive loads. Working memory available at the moment of a takeover request will largely determine the capability of a driver to safely operate an automated vehicle. If designed inappropriately, an in-vehicle message may be presented with poor timing and contribute to driver cognitive load; for example, presenting novel service logo information when a takeover is required, as a vehicle exits a highway. Instead, such messaging could be provided in advance when driver cognitive load is low during highway driving. Such a design could potentially mitigate changes in driver cognitive load.