When a truck breaks down on a highway during the daytime, what should the driver set out?

When a truck breaks down on a highway during the daytime, the best practice for the driver is to set out red triangles. Red triangles serve as an effective warning device, indicating to other drivers that there is a disabled vehicle on the highway. The color red is particularly visible and universally recognized as a signal for caution, especially in emergency situations.

Placement of these triangles also follows specific guidelines, which typically recommend placing them behind the vehicle at a distance to give oncoming traffic enough warning of the hazard. This is crucial for enhancing safety on the road and preventing additional accidents.

While flashing lights and warning cones can have their uses, they may not offer the same level of visibility or serve the standardized function of visual warning at a breakdown. White flags do not convey the necessary warning and are not appropriate for this scenario. Therefore, red triangles are the standardized and safest choice for signaling a breakdown on the road.