When merging onto a road, it is essential to consider the **position, trajectory, and speed of all vehicles and users** already traveling on it. This is due to several reasons:

- **Safety when entering a road:** Before performing the merging maneuver, it is crucial to observe the traffic and the road, both directly and through the rearview mirrors. This allows you to ensure that you can perform the maneuver safely for yourself and others.

- **Yielding:** When merging, you must yield to vehicles already on the road, ensuring that you do not become an obstacle for them. This involves adapting to their speed and trajectory to avoid risky situations.

- **Communication with other drivers:** It is important to inform other drivers of your intention to merge, using the vehicle's lights or hand signals. This helps other drivers be aware of your movements and facilitate the maneuver if necessary.

- **Facilitating the entry of other vehicles:** Drivers already on the road also have the responsibility to facilitate the entry of other vehicles, especially those that are larger or carrying many people, such as buses.

In summary, when merging onto a road, it is essential to consider **all vehicles and users** traveling on it to ensure a safe and smooth maneuver.