What must a driver do if they experience a failure in the braking system?

When a driver experiences a failure in the braking system, the most crucial and immediate action is to lower the vehicle's speed gradually. This helps to maintain control of the vehicle and prevents a potentially dangerous situation from escalating. By gently decelerating, the driver can reduce the momentum and make it easier to maneuver the vehicle safely to the side of the road or into a safe stopping area.

Slowing down can also allow the driver to assess the situation more adequately and prepare for further actions, such as using an alternative braking method, if available, or choosing a safe spot to come to a complete stop while reducing risk to themselves and others on the road.

The other options, while they could be part of broader safety practices, do not address the immediate need to control the vehicle's speed effectively. Alerting emergency services is important after ensuring the vehicle is under control, and attempting repairs on site can be risky and impractical without proper tools and expertise. Activating hazard lights is crucial for alerting other drivers of a problem but should be done after the driver has already taken measures to ensure safe vehicle operation.