Vehicular Fog Computing (VFC) has emerged as a promising solution to overcome the resource limitations of vehicles and the edge. The computing and storage capacity of vehicles can be used as infrastructure in the VFC system. Some applications in vehicular networks are real-time and complex such as augmented reality (AR) and online games. Therefore, vehicles that do not have enough resources to perform their tasks can offload them either partially or completely to moving and parked vehicles via direct and indirect wireless communications. It is critical to find an optimal solution for task offloading and task allocation problems in Vehicular Fog Networks (VFNs) where fog nodes can be static or dynamic. Task offloading strategies promote Quality of Service (QoS) and resource utilization in the network. Due to the high dynamicity of vehicular networks and the demands of users, task offloading can be problematic. There are few survey papers that address task offloading in VFC in variety aspects coherently. Hence, in this paper, different approaches for optimal task offloading are classified and analyzed deeply. We provide a comprehensive survey on related proposed the task offloading techniques by many researchers in VFC area. Also, we discuss about the advantages and weaknesses of related methods, common performance evaluation parameters and simulators. Finally, open issues and conclusions are defined for future search directions.

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