What is the best action if a car disappears from your rearview mirror while changing lanes?

The best action if a car disappears from your rearview mirror while changing lanes is to wait until you are confident it is not in your blind spot. This is crucial for ensuring safety on the road, as vehicles can quickly close in or be positioned in a way that they are not visible in your mirrors. By taking the time to ascertain whether the vehicle is still nearby, you reduce the risk of a collision during your lane change. It is essential to ensure that the area is clear, as vehicles in your blind spot can pose a significant danger.

Other actions like changing lanes immediately or accelerating to pass could lead to dangerous situations if the vehicle is still in close proximity and not visible to you. Additionally, although looking back over your shoulder can be helpful, it should be part of a thorough check of your surroundings rather than the sole action taken. The combination of checking your mirrors, blind spots, and using caution will provide the best assurance for safe lane changes.