<p>Unmanned aerial vehicles (UAVs), commonly known as drones, have played a crucial role in applications ranging from environmental monitoring to rescue operations. In recent years, their use in commercial services, especially for deliveries, has become an area of great interest due to the potential to reduce costs, increase transport speed, and expand reach in hard-to-reach locations, including densely populated urban areas. This advance represents a significant development in the evolution of logistics, introducing new operational paradigms that connect technology and efficiency. Yet, the use of drones in urban environments is not without its challenges, particularly in the realm of safety. The high density of obstacles, the presence of multiple aerial devices, and the unpredictable nature of environmental conditions all contribute to an increased risk of collisions. This risk, if left unaddressed, could significantly impact the performance and reliability of operations. It is therefore imperative that we investigate existing approaches and propose strategies that seamlessly integrate technological advances with operational safety. This study presents a systematic literature review to explore the causes of collisions and prevention strategies in the context of drone delivery services. From an initial analysis of 533 papers, 34 primary studies were selected for a detailed assessment. The work classifies the adopted approaches, such as types of delivery, collision types and causes, forms of detour, as well as the papers contributions and adopted evaluation. Based on the presented review, we highlight the research challenges and remaining research gaps. The analysis results in a comprehensive taxonomy and visualizations that help in understanding the state of the art, pointing out future directions to improve the safety and efficiency of drone delivery operations.</p>