The **seat belt** is a fundamental element of **passive safety** in vehicles. Its use is **mandatory for all occupants** of a vehicle that has seat belts installed, both drivers and passengers, on **all roads and streets**. This is because the seat belt protects people in the event of a sudden impact or if the vehicle overturns, preventing them from moving from their seats or being ejected from the vehicle. Wearing it correctly significantly increases the chances of surviving an accident.

There are some exceptions where it is not mandatory to wear the seat belt, such as when driving within a town or city in specific situations (for example, taxi drivers on duty or delivery drivers). However, these exceptions do not apply on roads, highways, or motorways, where it is always mandatory.

In summary, the seat belt is **mandatory on all roads** to ensure the safety of all vehicle occupants.