To understand why it is mandatory to have the **low beam headlights** on when driving on a **reversible lane**, it is important to know some rules about the use of vehicle lights.

- **Reversible lane**: It is a lane that can change direction according to traffic needs. This means that sometimes you can drive in one direction and other times in the opposite direction.

- During the day, it is mandatory to turn on the low beam headlights when driving on a reversible lane. This is because these lanes can present risk situations due to changes in direction, and the lights help improve visibility and alert other drivers of our presence.

- Additionally, low beam headlights are necessary in other situations such as when passing through tunnels or additional lanes temporarily created by construction or accidents, as these conditions can also affect visibility.

Therefore, when driving on a reversible lane during the day, it is essential to turn on the low beam headlights to ensure safety and comply with traffic regulations.