Which of the following areas must vehicles transporting placarded hazardous materials avoid?

Vehicles transporting placarded hazardous materials must avoid tunnels, narrow streets, and heavily populated areas primarily due to safety concerns. Each of these environments presents unique risks in the event of an accident or spill.

In tunnels, the confined space can exacerbate the effects of a hazardous material release, creating a situation where ventilation issues may lead to a rapid buildup of harmful fumes or increased fire risk. Additionally, exit routes in tunnels may be limited, complicating evacuation efforts.

Narrow streets can pose challenges for maneuverability and may heighten the risk of collisions. If an accident were to occur in a narrow street, the likelihood of causing damage to nearby structures or injuring pedestrians increases significantly.

Heavily populated areas likewise raise serious safety concerns. The potential for a larger number of casualties in the event of an incident involving hazardous materials is much higher in these regions. Incidents could lead to evacuation challenges and emergency response difficulties, further complicating the situation.

By avoiding all of these areas, those transporting hazardous materials contribute to minimizing risks to public safety and ensuring that emergency response can be effectively executed in the event of an incident, which is why the correct answer encompasses all these locations.