# Advances of UAVs toward Future Transportation: The State-of-the-Art, Challenges, and Opportunities
## 3 State of the Art of Practice and Research
### Challenges and Opportunities
In these situations, the use of partial external inputs to guide the UAVs might be recommended [15]. For efficient healthcare and relief operations, UAVs and UGVs can be integrated and automated for seamless and faster operations [105]. UGVs can be used for bulk transportation of heavy goods and people. UAVs can be deployed to deliver relief supplies like medicine, hygiene products, food, and water to the affected regions. Additionally, it is not easy to fly UAVs in harsh natural environments, with high wind and obstacles. Some UAVs are now equipped with collision technology to prevent UAVs from colliding with trees, buildings, or other obstacles [106]. However, the inherent problem of controlling UAVs in harsh weather conditions remains a challenge, although a lot of effort has been directed towards the advancements of robust UAV controllers in these situations. In response to traffic congestion, an urban transportation system that moves passengers or cargo by air via highly automated aircraft is being envisioned. This system is known as 'Urban Air Mobility' (UAM), and it will mainly consist of electrical VTOL UAVs [107]. Advanced Air Mobility (AAM) is conceptualized as an extension of UAM that will encompass transportation to longer distances and geographically distant regions. FAA is working towards identifying infrastructure needs and operational frameworks for UAM and AAM, and these systems will become an essential part of our transportation system in the near future [108]. In addition to the technological advancements, a lot of new policies and regulations have to be carefully developed. There is a need to implement a safe, reliable, and efficient use of UAVs in the airspace. In the future, the airspace will be crowded with UAVs for multiple purposes and applications. Additionally, UAVs need to share airspace with current manned aircraft and spacecraft. The current traffic management systems for the ground, water, and rail are not adequate for managing airspace. Preliminary research on the UAV traffic management (UTM) system is actively being conducted in various countries--the US, China, Taiwan, Korea, Sweden, and India, to name a few; but these research works are still at a prototype stage [107, 109, 110, 111, 5]. The goal of UTM is the safe integration of UAVs in the low-altitude air traffic, and it focuses on strategic deconfiction of multiple aircraft [107]. This can be achieved by employing digital sharing of planned flight details of the UAVs present in the airspace for situation awareness of all the operators. Ideally, UTM should be fully autonomous, and direct human input in busy urban UTM operations should be minimal [113]. Figure 9 represents a conceptual diagram of low-altitude UTM, adapted from Ref. [114]. In this section, the recent UAV research and applications in the transportation sector are discussed and summarized, and some of the key challenges are identified. UAVs are slowly being integrated and deployed in the transportation sector with promising results, and the potential to expand UAV applications in this sector keeps on increasing.