**Special vehicles** that travel on public roads must use a **yellow rotating light** when their speed does not exceed **40 km/h**. This light is important because it alerts other drivers to the presence of these vehicles, which are usually performing improvement or maintenance work on the road.

- The maximum speed allowed for these vehicles on **roads** is **40 km/h**.
- On **motorways and dual carriageways**, these vehicles cannot travel, except when performing specific work, and must use the yellow light from the moment they enter until they reach their destination.

Therefore, the yellow rotating light must be used whenever the speed does not exceed 40 km/h, regardless of whether it is day or night.