What is a crucial requirement for a vehicle operating in heavy smoke?

A crucial requirement for a vehicle operating in heavy smoke is for all vehicle lights to remain on. This measure significantly enhances the visibility of the vehicle to other drivers and emergency responders in low-visibility conditions caused by smoke. When smoke obscures vision, it becomes essential for the safety of both the vehicle's occupants and others on the road to be clearly seen. Operating with lights on helps prevent accidents and ensures that rescue or support teams can locate the vehicle quickly if needed.

In contrast, while having windows open might improve immediate visibility, it can also expose occupants to hazardous air quality. Locked doors are important for ensuring safety and security but do not contribute to visibility or operational safety in smoky conditions. Similarly, while ensuring there is clear exhaust is important for vehicle operation in general, it does not directly address the critical need for visibility in heavy smoke situations. Thus, keeping the vehicle lights on is the most effective step for safety in such an environment.