# Impact of Dual-Depth Head-Up Displays on Vehicle Driver Performance
## 1 Introduction  
Driving is a work of multiple perceptions, including vision, hearing, touch, etc. According to past studies, many accidents are caused by distraction or fatigue [1]. Although the use of a head-up display has been proven to distract drivers [2; 3; 4], it can reduce the number of times the driver looks down at traditional instruments and reduce the time of eye movement [5; 6]. By focusing on the road's condition to reduce the driver's fatigue, so to reduce the driver's burden, the development of driving assistance equipment has become an important issue. To reduce the mental burden and visual fatigue of driving, the Oldsmobile Automobile Company produced the first car equipped with a head-up display in 1988, which used a vacuum fluorescent tube (VFD) and optical reflectors to generate a speed indicator and virtual image [7], and projected the information on the windshield glass in front of the driver, in the driver's field of vision, in an attempt to reduce the driver's mental burden and visual fatigue. At present, most of the navigation information is displayed through the screen or head-up display (HUD). In recent years, to reduce the burden on drivers, many researchers project a lot of driving information on the HUD screen and try to project navigation information in the distance. From the traditional single-depth head-up display to the present AR-HUD, the HUD has gradually become one of the auxiliary devices of today's cars. As the line of sight is an important factor for driving, [PERSON] et al. studied the influence of the HUD's position, distance, font size, brightness, and color on driving line of sight [5]. Comparing city and highway driving viewpoint positions, the results show that screen-fixed and world-fixed ICONS, where the plane of sight is located within a 5-degree radius of the eye's fovea, are annoying to drivers. To solve the problem of HUD clutter and its possible negative effects and maximize the benefits of the HUD, [PERSON], and [PERSON] et al. used two HUDs as display modes [8]: one wasresponsible for displaying the screen below the line of sight, and the other displaying the screen superimposed in front of the driver's field of vision. Thus far, the multi-depth HUD has been gradually developed to realize the concept of the AR HUD [9]. The AR HUD can provide an interface for a more intuitive and immersive experience [10]. Compared with the traditional HUD, the AR HUD can identify the turning position earlier [10]. According to the research of [PERSON] et al., increasing the viewing distance and size can improve cognition and performance [11]. Although the AR-HUD can improve the driver's understanding of the real world, empirical studies have also pointed out that the AR-HUD graphics' prominence, frequent changes, and visual confusion will attract the driver's attention [2]. Avoiding the distraction caused by information depends on the graphical elements on the display and the perceptual form of the interface [2, 12]. Since vision is a highly complex task, many factors must be considered in designing HUD information, such as color, position, size, light source, background complexity, etc. [9]. Human eye visual perception:  
Visual perception has a moderate to high correlation with driving results [13, 14]. Visual perception is easily affected by many reasons, such as depth and distance perception [15, 16, 17], color contrast [18], environmental complexity [19], light source [20], etc. To solve the problem caused by looking down at the instrument information while driving, the eyes need to focus repeatedly on a closer distance; numerous studies have demonstrated that the frequent switching of eye pairs' focal distance will increase visual fatigue [21, 22, 23]. [PERSON] et al.