What should you do if you observe a vehicle swerving in and out of lanes?

Reporting a vehicle that is swerving in and out of lanes is the appropriate action because this behavior often indicates that the driver may be impaired or experiencing a medical emergency. When you notice erratic driving, it poses a significant risk to the driver, their passengers, and other road users. By informing law enforcement, they can take the necessary measures to ensure safety, which could involve stopping the vehicle to assess the situation and providing assistance if needed.

Not acting upon this observation could allow a potentially dangerous situation to escalate, jeopardizing the safety of everyone on the road. Ignoring such behavior, as suggested in one of the choices, poses a risk since normal driving patterns do not typically include swerving. Additionally, signaling to the driver may not have the intended effect and could further complicate the situation. Following the vehicle closely can be unsafe and may even lead to additional accidents. Thus, reporting to law enforcement is the safest and most responsible course of action.