What should be activated by any truck or trailer parked upon a roadway if it exceeds specific dimensions?

Answer: B — Hazard warning lights

When a truck or trailer exceeds specific dimensions and is parked on a roadway, the activation of hazard warning lights is essential for safety. This is because hazard warning lights serve to alert other drivers of a potential obstruction or hazard in the roadway. The use of hazard lights is a common practice to indicate that the vehicle is not moving and poses a caution to oncoming traffic, especially in situations where visibility is compromised, such as at night or in poor weather conditions. In addition to signaling that the vehicle is parked and may not be immediately visible, hazard warning lights help in ensuring that other drivers can assess the situation from a distance, allowing them to reduce speed or change lanes to avoid the stationary vehicle. This is particularly important for larger vehicles, which might take up more space on the roadway and pose additional risks to other drivers. While brake lights serve to indicate stopping, parking lights are typically used when a vehicle is parked in a specific way, such as on the side of a road, and headlights are primarily used for illumination when driving at night. However, none of these options provide the broad alert needed which hazard warning lights do when a larger vehicle is stationary on the roadway.