Drivers' urge to access content on smartphones while driving causes a high number of fatal accidents every year. We explore 3D full-windshield size head-up displays as an opportunity to present such content in a safer manner. In particular, we look into how drivers would personalize such displays and whether it can be considered safe. Firstly, by means of an online survey we identify types of content users access on their smartphones while driving and whether users are interested in the same content on a head-up display. Secondly, we let drivers design personalized 3D layouts and assess how personalization impacts on driving safety. Thirdly, we compare personalized layouts to a one-fits-all layout concept in a 3D driving simulator study regarding safety. We found that drivers' content preferences diverge largely and that most of the personalized layouts do not respect safety sufficiently. The one-fits-all layout led to a better response performance but needs to be modified to consider the drivers' preferences. We discuss the implications of the presented research on road safety and future 3D information placement on head-up displays.