Augmented Reality (AR) navigation via Head-Mounted Displays (HMDs), particularly AR glasses, is revolutionizing the driving experience by integrating real-time routing information into the driver's field of view. Despite the potential of AR glasses, the question of how to display navigation information on the interface of these devices remains a valuable yet relatively unexplored research area. This study employs a mixed-method approach involving 32 participants, combining qualitative feedback from semi-structured interviews with quantitative data from usability questionnaires in both simulated and real-world scenarios. Highlighting the necessity of real-world testing, the research evaluates the impact of five icon placements on the efficiency and effectiveness of information perception in both environments. The experiment results indicate a preference for non-central icon placements, especially bottom-center in real world, which mostly balances distraction and workload for the driver. Moreover, these findings contribute to the formulation of four specific design implications for augmented reality interfaces and systems. This research advances the understanding of AR glasses in driving assistance and sets the stage for further developments in this emerging technology field.