What should be used to indicate a vehicle is stopped for emergency reasons on a roadway?

Using flares or safety triangles is the optimal method for indicating that a vehicle is stopped on a roadway for emergency reasons. These tools are specifically designed to alert other drivers of a hazard, enhancing visibility in various conditions, especially at nighttime or during inclement weather.

Flares create a bright, visible light that can be seen from a distance, signaling to approaching vehicles to slow down or steer clear. Similarly, safety triangles are reflective and highly visible, serving the same purpose but without the need for a flame. Their placement on the roadway at a safe distance from the vehicle proactively warns oncoming motorists of a potential danger ahead, which is crucial in preventing secondary accidents.

The other options, although they may offer some degree of visibility, do not provide the same level of effective warning as flares or safety triangles. Warning lights may alert some drivers, but they do not convey the urgency of a stopped vehicle as effectively as flares do. Hazard signs placed on the vehicle itself may be useful in some contexts but can be less visible to approaching traffic. Reflective tape can help increase visibility but does not stand out as much as more pronounced emergency signaling methods.