In which situation is it mandatory to use a vehicle's reflective triangles?

Using reflective triangles is a crucial safety measure for alerting other drivers to a stationary vehicle, particularly when it is situated on the side of the highway. This is especially important because vehicles parked in such locations can be unexpected hazards for other drivers. The triangles help enhance visibility in various conditions, thereby reducing the risk of collisions.

When a vehicle is parked on the side of the highway, it is generally considered to be in a potentially dangerous position, as other drivers may not anticipate an immobile vehicle in the travel lane. Setting up reflective triangles at specified distances behind the vehicle (and also in front, if applicable) serves to create a visible warning area, helping to ensure the safety of both the driver who is possibly exiting the vehicle to seek help and other motorists driving in the vicinity.

Other scenarios involving heavy rain, vehicle repairs, or transporting hazardous materials may require caution and specific safety measures, but they do not have the same direct legal requirement for the use of reflective triangles as when a vehicle is parked on the side of the highway.