## 3 Results
### Comparing Task Performance in the Familiar and the Unfamiliar Car  
Before comparing participants' interactions with the vehicle in their own car versus the unfamiliar car, it was first established that each participant's own vehicle was indeed more familiar to them than the car that was brought by the experimenter. This analysis has been described in more detail in the _Materials_ section as part of the paragraph titled _The cars_. The most frequently performed task while driving was using the direction indicator. This was the case for both the familiar car as well as the unfamiliar car, with an average frequency of 66.2 and 66.6, respectively. For the familiar car, the next most-used tasks were found to be changing the volume, moving the sun visor, changing the temperature of the climate-control system and changing the front windshield wiper speed, with average frequencies of 2.7, 1.7, 1.7 and 1.6, respectively. For the unfamiliar car, the most performed tasks after changing the direction indicator were changing the front windshield wiper speed, adjusting the volume, changing the speed of the rear windshield wiper and moving the sun visor. The average frequencies were 6.9, 1.6, 1.6 and 1.2, respectively. For the unfamiliar car, higher frequencies can be found for tasks that are related to setting up the car, compared to in the familiar vehicle. Examples of these tasks are adjusting the rear-view mirror as well as the seat. These were adjusted 0.7 and 0.4 times per hour of driving, respectively, compared to 0.1 and 0.1 times in the familiar car. Figure 3 shows the average frequencies of the most performed tasks in both the familiar versus the unfamiliar car, whilst Figure 4 presents the same comparison but on the aggregated level of the function categories. To understand whether function usage differs between driving a familiar or an unfamiliar car, paired-samples \(t\)-tests were performed on the function category level. An overview of the results of these paired-samples \(t\)-tests is provided in Table 5. When looking at the aggregated function category level again, it shows that the three categories with the highest average task frequencies are the same for the familiar and the unfamiliar car. These are the categories for tasks related to the lights, the windshield and to radio and media, respectively. Figure 4: Aggregated task frequencies per function category, comparing the familiar car and the unfamiliar car. Figure 3: Average use frequencies for the most frequently performed tasks, comparing the familiar car and the unfamiliar car. Excluding the most frequently used task: the direction indicator, with an average use frequency of 66.22 per hour for the familiar car and 66.58 per hour for the familiar car. with average frequencies of 66.3, 4.5 and 3.8 for the familiar car and 66.9, 9.9 and 2.7 for the unfamiliar car, respectively. However, the fourth most frequently used category of tasks differs between the familiar and the unfamiliar car. For the familiar car, the fourth category with the highest task frequencies is the climate-control category. When driving their own car, on average participants used functions in this category 3.5 times per hour compared to 0.4 times per hour in the unfamiliar car, which is significantly less (\(p<0.001\)). On the other hand, in the unfamiliar car, the fourth most used category of tasks is the setup category. In the unfamiliar car, participants engaged in tasks from this category significantly more often than in the familiar car (\(p=0.03\)), with an average frequency of 1.0 times per hour when driving the unfamiliar car compared to 0.2 times in their own car. Note however, that the trip took approximately half an hour. Next to differences in individual functions, it is also of interest to understand whether function usage in general differs between driving your own car or an unfamiliar car.