What is the primary function of a vehicle's brake system?

The primary function of a vehicle's brake system is to slow down and stop the vehicle. The braking system is designed to provide the necessary force to reduce the vehicle's speed or bring it to a complete stop when required. This is critical for safe operation, allowing the driver to respond to various situations on the road, such as stoplights, obstacles, and changing traffic conditions. Effective braking ensures that the vehicle can operate safely and within legal speed limits, contributing significantly to road safety.

In contrast, the other functions listed do not accurately reflect the purpose of the brake system. Accelerating and maintaining speed are functions that relate to the engine and powertrain, whereas improving fuel efficiency pertains to optimizing engine performance rather than the braking process. The focus of the brake system is solely on deceleration and stopping.