To understand why it is possible to drive on the left of a **solid line** on a **one-way road**, it is important to know the rules about lines and markings on roads.

- **Solid line**: Generally, this line prohibits drivers from crossing it or driving over it. However, this restriction mainly applies on **two-way roads**. On these roads, you should not drive to the left of the solid line to avoid conflicts with oncoming traffic.

- On a **one-way road**, all lanes go in the same direction. Therefore, there is no risk of encountering vehicles coming from the opposite direction. This allows drivers to drive on the left of a solid line without violating traffic rules.


In summary, the key is the type of road: on a one-way road, driving on the left of a solid line is allowed, as there is no opposing traffic.