Vehicles for **people with reduced mobility** must travel on the **shoulder** whenever possible and if it is wide enough. This is because, if there is no road or part of it specifically designated for them, they must use the shoulder, just like other vehicles such as bicycles, mopeds, and light special vehicles.

- The **shoulder** is the part of the road located next to the main lanes, and it is intended for certain vehicles that cannot travel on the normal lanes.

- If the shoulder is not practicable or not wide enough, these vehicles may use only the essential part of the lane.

Therefore, the correct option is that vehicles for people with reduced mobility must travel on the shoulder whenever it is possible and safe to do so.