## 4 Discussion and Conclusions  
This study showed that, regardless of the car being familiar to the driver or not, the direction indicator is by far the most frequently used function. Other frequently performed actions include adjusting the volume of the radio, moving the sun visor, adjusting the temperature and changing the wiper speed. The factors that influenced the task frequencies included car familiarity, gender, age and weather conditions. Unsurprisingly, rainy weather triggered an increase in wiper usage and sunny weather resulted in increased use of the sun visor. Men, younger drivers and drivers familiar with the car were more likely to use HMI functions related to radio and media. As radio and media tasks are optional (i.e., not required to use in order to safely drive the car) and mostly for entertainment purposes, it seems that older people choose to perform these tasks less [19]. The same reasoning might be true for those not familiar with the car, as a means to self-regulate the task load. Women, on the other hand, were more likely to use HMI functions related to climate control. This could be because women have been found to be more perceptible to cold [22]. In more modern cars, it appears that drivers have fewer interactions with their vehicle's HMI, possibly because more functions can be put on auto mode. An exception is the usage of the Autopilot function. Despite the fact that only two out of the thirty participants were driving a car with this function, the engaging and disengaging is comparatively prominent in the overview of average use frequencies per task. This suggests that this function triggers a significant amount of interactions while driving. In general, drivers familiar with a car were more likely to engage with its HMI functions compared to when driving an unfamiliar car. Possibly, participants are more comfortable in a familiar car and therefore more confident that they can perform these tasks safely while driving. This behavioural adaptation may indicate that drivers find driving in an unfamiliar car more effortful and that they try to regulate their mental load by using fewer functions. This can be seen as a form of self-regulation, where people only perform tasks when they think they can safely perform them [23]. Contrary to good driving practices, it was also found that, in the unfamiliar car, participants continued adjusting their seat as well as the rearview mirror while driving. [PERSON] et al. [5] found that driving an unfamiliar car increased crash risk by 204.5 times. In the current study, it was found that driving an unfamiliar car may also result in increased distraction when the design of the car is unintuitive. Multiple participants driving the unfamiliar car struggled to set the front windshield wipers to an interval due to the unfamiliar design. This example shows that a lack of standardisation can result in an unnecessary high number of interactions, thus causing distractions [24; 25]. As part of their study, the UDV [8] pointed out that currently 'there are no regulations or mandatory best practice that define how to design increasingly complex HMIs that distract drivers as little as possible from their driving task'. In fact, when HMIs are addressed in regulations, the focus is mostly on symbols and telltales only [26], such as UN R121, including its 01 series of amendments [27]. As a result, there is much variety in HMIs across different brands. Standardisation is also lacking, and this is often mentioned as a problem in the literature [24; 25], as it can result in reduced safety, particularly when driving unfamiliar cars. This is backed up by naturalistic driving research, which finds that crash risk increases when driving unfamiliar cars [5; 28]. This lack of standardisation could become an even bigger problem due to a growing number of people who are using services such as car sharing, where they are driving unfamiliar cars [29]. A limitation of the current study is that each participant drove their own selected route.