# Unmanned Aerial Vehicle Routing Problems: A Literature Review
###### Abstract  
Unmanned aerial vehicle (UAV) routing is transitioning from an emerging topic to a growing research area as the 3D flexible utilization of airspace, promogulated by UAVs, is a potential game changer in solving the urban air mobility challenge by allowing to reshape transportation and logistics in the future. This has revealed a need to classify different types of research and examine the general characteristics of the research area. This research aims to assist in identifying the main topics and emerging research streams and provides a published overview of the current state and contributions to the area of the UAV routing problem (UAVRP) and a general categorization of the vehicle routing problem (VRP) followed by a UAVRP classification with a graphical taxonomy based on the analysis of UAVRP current status. To achieve this, an analysis of the existing research contributions promulgated in this domain is conducted. This analysis is used to identify the current state of UAVRP and the gaps related to the UAVs' flight dynamics and weather conditions, which significantly influence the fuel consumption of the UAV when modeling the UAVRP.  
unmanned aerial vehicles; UAV routing and scheduling; UAV routing; vehicle routing problem [1] [  
purposes due to the improved maneuverability and high flight efficiency when compared to both the multirotor and fixed-wing systems. The hybrid UAVs system is a combination of the multi-rotor and fixed-wing UAVs, and the combination of these two models has boosted its capabilities to allow vertical take-off and landing [8].  
Following recent advancements in UAV technology, Amazon, DHL, Federal Express, and other large companies with an interest in package delivery have begun investigating the viability of incorporating UAV-based delivery into their commercial services [9; 10]. UAVs have the potential to significantly reduce the cost and time required to deliver materials as, in general, they are less expensive to maintain than traditional delivery vehicles such as trucks and can lower labor costs by performing tasks autonomously [11; 12; 13; 14]. To support this emerging area, a new problem category arises, the UAV routing problem (UAVRP). Despite the increasing focus on UAVs and the field's status as an emerging technology, there is no comprehensive overview of the current state available in terms of the UAVRP characteristics and the methods used to solve UAVRP in the current state.  
The main objectives of this paper are to identify the unique characteristics of the UAVRP and present the first overview of the current state of research. This is achieved by analyzing the existing research contributions promulgated in this domain. Based on the analysis, we identify the current state of UAVRP and the challenges in current state of the general vehicle routing to address the specific nature of the UAVRP. Simultaneously, this paper also provides a published overview of the current state and contributions to the area of the UAVRP. The remainder of the paper is structured as follows: First, a general categorization of vehicle routing problem (VRP) is presented. An overview of UAVRP based on the analysis of UAVRP current state follows next. Section 5 presents an overview of identified challenges in the current state before presenting conclusions and avenues of further research.