What sign should vehicles, machinery, or combinations that travel at less than 40 km/h display?

Vehicles, machinery, or combinations that travel at speeds of less than 40 km/h are required to display a red triangle slow-moving vehicle sign. This sign is universally recognized and serves an important safety purpose. It alerts other drivers that the vehicle is traveling considerably slower than the normal flow of traffic, allowing them to take necessary precautions when approaching.

The red triangle is highly visible and is specifically designed to capture the attention of faster-moving vehicles, reducing the likelihood of accidents. This is especially critical in situations where slower vehicles may be on roadways that are frequented by higher-speed traffic.

The other options, while also identifiable as road signs, do not serve the same function for slow-moving vehicles. A yellow circular sign generally indicates caution or warning, but it does not specify the movement speed of the vehicle. A green square caution sign is not standard in this context, as green typically signals go or safe conditions. A blue rectangular sign usually provides information about services or places nearby rather than speed. Thus, the red triangle sign is the correct sign for this scenario, ensuring that slower-moving vehicles alert others on the road effectively.