# Review of Autonomous Intelligent Vehicles for Urban Driving and Parking
## 3 The Concepts of Autonomous Driving
### On the Road
The steering control can be achieved through an infrastructure-supported or autonomous approach. The infrastructure-supported system is based on physically or virtually marked trajectories, usually together with V2V communication. In the autonomous overtaking process, only onboard sensors are used to determine the relative position and orientation between vehicles. The vehicle steering control is determined according to the relative position and orientation concerning the vehicle to overtake. Thus, the overtaking vehicle accomplishes the maneuver concerning the overtaken vehicle instead of the road. This system can reduce numerous fatal crashes due to unsafe diversion space from the original lane, poor visibility when passing a vehicle, or erroneous judgment in returning to the lane [96]. By using V2I communication and positioning technology, the traffic controller/roadside infrastructure will have real-time awareness of the number of vehicles, their positions, and their speeds [97]. The autonomous vehicle will communicate with the traffic controller/roadside where information consists of the right of way [97] and allows planning of safe trajectory crossing the intersection [98]. A traffic controller communicates with individual vehicles and assigns specific time slots to pass the intersection after real-time information processing [99]. The controller functions as a virtual traffic light that can change at an infinite frequency [99], enabling intelligent traffic signal phase setting, unlike the current traffic light setting. With the current setting, vehicles are not allowed to cross the intersection if the light corresponding to their lane is red, even in the absence of conflicting vehicles [100]. This causes delay, fuel wastage, tailpipe emissions, and passenger frustration [101; 102]. In the nonsignalized intersection where there is no traffic light or other controlling facilities, vehicles first communicate with each other through V2V communication and negotiate intersection passing. Two categories of solutions can be adopted to manage such intersections: a cooperative resource reservation and a trajectory planning approach. The former focuses on scheduling space tiles and time slots requested by vehicles intending to cross the intersection. In contrast, the latter focuses on the relative motion between vehicles to determine a safe crossing sequence [103]. To achieve several functions, as discussed early, an autonomous vehicle's accurate localization system is required. As classified by [PERSON] et al. [6], localization techniques can be categorized by the mapping approach, the sensor-based approach, and cooperativelocalization techniques. The first method localizes vehicles concerning a reference global or local map. The sensor-based approach utilizes onboard vehicle sensors to find the global position of a vehicle in a specified coordinate system. The primary sensors involved are GPS, inertial motion units (IMUs), cameras, radar, light detection and ranging (LiDAR), and ultrasonic sensors. In the last method, the localization of vehicles is accomplished through broadcasting information of their current state. Through V2V and/or V2I communications, the vehicle can know the surrounding vehicles' exact location.