The **reaction time** is the interval that elapses from when a driver **detects a hazard** until they **apply the brake**. This concept is crucial for understanding how we react to unforeseen situations while driving.

- **Hazard detection:** It can be an obstacle, a traffic sign, or any other unforeseen event that the driver perceives visually or audibly.

- **Reaction:** The reaction time is measured from the moment the driver perceives the hazard until they take the action of braking. This time is usually **0.75 seconds** under normal conditions, although it can vary depending on factors such as the driver's physical and psychological state.

- **Factors affecting reaction time:** Fatigue, sleepiness, advanced age, vision or hearing problems, illnesses, alcohol or drug consumption, and other factors can increase the time it takes for a driver to react.

It is important to differentiate reaction time from other concepts such as **stopping distance**, which includes both the reaction time and the braking time until the vehicle comes to a complete stop.