## 3 Proposed AR HUD System  
### Gesture Recognition Control  
The utilisation of gestural controls as compared to conventional controls offers the advantage of performing control tasks without affecting the visual and cognitive attention required for driving [31]. Markedly, the gestures contain information that can be conveyed whilst minimally relying on vision, thus affording minimal \"eyes off the road\" time. Thus, gestural controls could be well placed for developing specific in-vehicle interaction tasks that can minimise driver distraction [32].  
Natural gestures, in particular, offer an additional advantage in their intuitive nature, as they are gestures commonly accompanying human to human conversation. Thus, they can be easily memorised and require minimal training, causing minimum cognitive driver workload. These qualities present them as a promising option for use with in-vehicle secondary controls [32].  
This has been documented in previous studies where participant drivers reported less distraction and had fewer errors in performance when utilising gestural controls as compared to haptic controls [31; 32; 33; 34; 35]. Unlike speech-based controls, gestural controls are not affected by noisy conditions, dialects, and accents that can be a source of error for speech-based controls [36].  
One of the most important benefits for the in-vehicle interface is the absence of physical contact with any form of screen or surface. As such, the driver is not required to focus his/her attention to touch a particular point in the HDD that could perform the required task as presented in previous studies [14; 15; 32]. Notably, the drivers of the studies mentioned above also favoured the gestural controls compared to conventional ones.  
Acceptance models have indicated that gestural controls would be readily acknowledged by the drivers for controlling secondary tasks if these can be performed with one hand without distraction [31; 32; 34].  
The above suggestion supports the hypothesis that gestures are a rightful alternative for the current paradigm of physical interaction by requiring minimum workload for operation and less continuous moves. Consequently, it could improve operation proficiency and increase road safety [34; 35].  
The functionality of a gesture-based system could, however, be affected if the gesture interfaces are not self-revealing, so the user has to know beforehand the specific set of gestures that the system recognises and the function that they correspond to. As such, it becomes more cumbersome for the user to memorise the correct gestural command set as the number of gestures increase. This is an evident problem with some early adaptations of gesture recognition technology by some automotive manufacturers. To avoid this issue, our proposed gesture recognition interface has been seamlessly coupled with a visual HUD interface, as seen in Figures 1 and 2.  
The development of the proposed AR HUD system entailed multiple iterations on the visual and gestural interface, as well as the positioning of the proposed AR symbols. The following subsections present the design and implementation considerations that led to the prototype system.