## 5 Simulation Results and Discussion
### Effect of Cooperative Lane Change
This is because vehicles do not decelerate to adjust their time headway in this model, so they tend to keep moving at high speed even when changing lanes, thus increasing traffic throughput. On the other hand, the safety and comfort levels of this model are low. This is because the vehicles do not adjust their time headway, so they need to decelerate rapidly in a short time. _Proposed_NoPrelim:_ In Scenario 30, _Proposed_NoPrelim_ shows little difference in fairness, safety, and comfort level compared with _Proposed_Full_, but has lower traffic throughput. This is because in _Proposed_Full_, vehicles in the free lane change lanes first in the preliminary avoidance zone to make space for vehicles in the closed lane to change lanes in the avoidance zone, and this reduces the number of times they need to slow down, compared with the case of _Proposed_NoPrelim_. _Proposed_NoAdaptive:_ _Proposed_NoAdaptive_ shows little difference compared with _Proposed_Full_ in all metrics. The reason is as follows. When the CV penetration ratio is 100%, temporary congestion around the obstacle rarely occurs because vehicles in the closed lanes change lanes with plenty of time to spare when _Proposed_NoAdaptive_ and _Proposed_Full_ are used. Therefore, strategy 1 (avoiding congested lane) has little chance to work. Additionally, the amount of traffic load input is the same in all lanes. Thus, the probabilities of changing lanes from the center lane to the left lane and from the center lane to the right calculated in _Proposed_Full_ are the same (50%) in Scenario 31. The results are the same for _Proposed_NoAdaptive_ when the lane is randomly selected. Note that the effect of the adaptive lane change can be seen when the CV penetration ratio is less than 100%. For scenarios with four or more lanes, Strategy 2 is expected to be more effective and provide an advantage over the random decision case. _Proposed_Full:_ _Proposed_Full_ achieves sufficiently high total traffic throughput in all scenarios. In addition, it achieves very high fairness, safety, and comfort level in all scenarios. However, it has lower traffic throughput than _Proposed_NoGapOpen_ in Scenarios 30 and 31, but higher traffic throughput in Scenario 20. This is because the control of doubling the time headway of vehicles in all three lanes is excessive, resulting in lower traffic throughput. Thus, it is expected that as the ratio of closed lanes to the total roadway lanes becomes smaller, the control of doubling the time headway of all vehicles will become excessive, and a lower traffic throughput will result. There is thus room for improving our method in the future. From these discussions, we can summarize the effect of the proposed cooperative lane change as follows:  
* Sharing information about the obstacle through V2V communication allows vehicles to adjust their speed and change lanes in advance, preventing rapid deceleration. * Adjusting the time headway of vehicles in advance is effective at significantly improving safety and comfort level in obstacle avoidance. * Shifting the lane change timing between vehicles in the closed lane and vehicles in the free lane by introducing a preliminary avoidance zone is effective in facilitating obstacle avoidance. * The proposed scheme achieves sufficiently high traffic throughput without degrading fairness, safety, or comfort level in the most balanced way. Note that we assume that vehicles' microscopic operation depends on the lane change model of SUMO. Therefore, the performance of the proposed scheme may vary depending on trajectory planning.