在两次召回后，美国机构结束了对Waymo自动驾驶汽车碰撞和意外行为的调查。

Core Viewpoint - The investigation into Waymo's autonomous vehicles regarding collisions and incidents has concluded after two recalls by U.S. agencies [1] Group 1 - The U.S. agencies ended their investigation into Waymo's self-driving cars after addressing safety concerns [1] - The investigation was prompted by reports of collisions and unexpected behaviors of the vehicles [1] - Waymo has conducted two recalls as part of the response to the investigation [1]