To understand why a vehicle that is going to be overtaken on the right on a two-way road must be positioned in the **center of the roadway without crossing the axis**, it is important to consider the overtaking rules and the obligations of the driver being overtaken.

- **Overtaking on the right**: In general, overtaking is done on the left. However, there are exceptions where overtaking on the right is allowed, such as when the vehicle to be overtaken is indicating a left turn or on urban roads with multiple lanes in the same direction. On a two-way road, these exceptions do not apply, so overtaking on the right is not common.

- **Obligations of the driver being overtaken**: The driver being overtaken must facilitate the maneuver. This includes **placing their vehicle on the right edge of the lane**, but without invading the shoulder. However, on a two-way road, it is crucial not to cross the axis of the roadway to avoid invading the opposite lane, which could cause an accident.

- **Safety on two-way roads**: On these roads, space is limited and the risk of head-on collision is higher. Therefore, keeping the vehicle in the center of the lane, without crossing the axis, ensures that there is enough space for the overtaking vehicle to perform the maneuver safely.

In summary, positioning in the **center of the roadway without crossing the axis** allows the overtaking to be carried out safely, respecting traffic regulations and avoiding dangerous situations.