Which item is a potential distraction that could affect driving performance?

Portable GPS devices are indeed a potential distraction while driving because they require the driver's attention to operate effectively. When using a GPS, drivers may need to interact with the device to input addresses, change routes, or monitor directions, which can divert their focus from the road and surrounding traffic. This momentary distraction can significantly increase the risk of an accident, especially if it leads to inattention to critical driving tasks such as maintaining speed, checking mirrors, or observing traffic signals.

In contrast, wearing a seat belt is a safety feature that keeps drivers secure and does not distract them from driving. Traffic signals are essential indicators of road rules and do not require interaction that could distract a driver, while having properly adjusted side mirrors enhances visibility and safety without being a distraction.