**Special vehicles** are those that perform construction or special services on the roads. These vehicles must have a **yellow light on** so that other drivers can easily identify them. However, they do not have priority to pass or overtake other vehicles.

- When these vehicles are not in urgent service, they must travel on the **carriageway**, which is the part of the road intended for vehicle traffic.
- The **median** is a strip that separates the directions of traffic on highways and expressways, and it is not intended for regular vehicle traffic.
- The **shoulder** is a part of the road reserved for emergencies or to stop in case of necessity, not for normal vehicle circulation.

Therefore, special vehicles must travel on the **carriageway** when they are not in urgent service.