On a two-way road where lanes are not marked, it is **mandatory to drive on the right, as close as possible to the edge of the road**. This is due to several reasons:

- **Safety and visibility:** Driving on the right allows vehicles coming in the opposite direction to have their space free, especially on curves and crests where visibility is reduced. This helps to avoid head-on collisions.

- **General regulations:** On roads where lanes are not marked, all drivers must follow this basic rule of driving on the right. This applies both in urban and rural areas, ensuring an orderly and predictable flow of traffic.

- **Specific exceptions:** Although some vehicles, such as bicycles or mopeds, have certain exceptions in specific situations, the general rule for cars is to stay on the right.


In summary, driving on the right and close to the edge of the road is a fundamental safety measure that facilitates traffic and reduces the risk of accidents on two-way roads without marked lanes.