What must vehicles transporting flammable gases or liquids use instead of flares?

Vehicles transporting flammable gases or liquids must use triangular reflectors instead of flares for several critical safety reasons. Flares can ignite flammable vapors and pose a significant fire hazard during transport or in the event of an accident. Triangular reflectors, on the other hand, serve as a visible warning to other drivers while eliminating the risk of ignition from an open flame. They are effective in marking the presence of a stopped or slow-moving vehicle, especially in low visibility conditions without introducing the additional risk that a flare would.

The use of triangular reflectors aligns with safety regulations, ensuring that proper precautions are taken when transporting hazardous materials. Each of the other options does possess some utility in different scenarios, but they do not meet the specific need for vehicles carrying flammable substances to signal their presence safely without the risk of fire.