## 1 Introduction  
In recent years, safe driving support and automated driving technology using vehicle-to-vehicle (V2V) communication have been actively studied. The methods used in these studies are expected to improve the safety and efficiency of traffic flow because vehicles can cooperate by sharing their position, speed, and other driving information with surrounding vehicles [1]. If an obstacle (e.g., a disabled vehicle or spilled cargo) suddenly blocks part of a multilane road, a traffic jam may occur because of the decrease in the road capacity [2]. Even if the road capacity after the blockage is larger than the offered road traffic, traffic jams may occur because vehicles in the blocked lane need to move to the neighboring lane, which leads to the sudden deceleration of vehicles [3] as shown in Figure 0(a). In this situation, if the vehicle that detected the obstacle immediately notifies the following vehicles of the obstacle's position by using V2V communication, the following vehicles will be able to take action to avoid the obstacle in advance, thereby preventing a traffic jam, as shown in Figure 0(b). Currently, the existence of an obstacle on the road is notified to drivers via the internet (e.g., Google Maps [4] and Waze [5]), broadcast system (e.g., VICS--vehicle information and communication system [6]), and roadside digital signboards. If someone, e.g., general drivers or a road operator, finds an obstacle on the road, the control center is notified of the information. Then the information is presented to drivers via car navigation systems, smartphone apps, and roadside signboards. Since there is a non-negligible delay between the detection of the obstacle and the time that the information reaches vehicles approaching the obstacle, drivers and autonomous vehicles moving near the obstacle cannot react to the obstacle quickly. Even if the existence of an obstacle is notified to drivers/autonomous vehicles, they do not know the best operation, e.g., acceleration or which lane to change to, to avoid the obstacle, not leading to traffic jams. On the other hand, the proposed method enables the vehicles moving in a wide range behind the obstacle to know the existence of the obstacle and how to react to it properly (e.g., making space to accommodate lane-changing vehicles and selecting a lane), not leading to traffic jams and uncomfortable driving maneuvers. Since the notification is sent to vehicles in a wide range, even human drivers can react to it with time to spare. Our previous work [7] proposed a simple rule-based lane change control strategy for the smooth avoidance of a suddenly appearing road obstacle by using V2V communication. In this strategy, the vehicle that detects an obstacle uses multi-hop communication to share the obstacle's position with the vehicles behind it. Vehicles behind the obstacle that receive the message decrease their speed to double the normal time headway so that vehicles in the blocked lane can change lanes smoothly and safely, as shown in Figure 2. In the simulations of a two-lane road using the traffic flow simulator, simulation of urban mobility (SUMO) [8], this scheme improves traffic throughput and fairness among lanes compared with the scheme using only non-connected vehicles (NCVs). Figure 1: Obstacle avoidance using V2V communication. (**a**) Avoidance strategy when the obstacle’s existence cannot be shared via V2V communication. (**b**) Avoidance strategy when vehicles share the obstacle’s existence and location using V2V communication. Figure 2: Control rules based on distance between an obstacle and approaching vehicles on a two-lane road. However, this strategy only considered a two-lane road. This paper extends this strategy to work when one lane is obstructed on a three- or more lane road. When the three-lane road's rightmost (edge) lane is obstructed, if only vehicles in the rightmost lane change lanes, traffic will concentrate in the center lane.