What are spring brakes primarily used for?

Spring brakes are primarily used as emergency and parking brakes in commercial vehicles. They utilize a powerful spring mechanism that engages the brakes when the air pressure in the brake system drops below a specific threshold. This design ensures that the brakes activate automatically in emergency situations, such as when there's an air system failure, ensuring that the vehicle remains stationary and preventing it from rolling away.

In addition to serving as an emergency measure, spring brakes are also extensively utilized for parking. When the vehicle is parked, the spring brakes can be engaged to securely hold the vehicle in place, providing safety and stability. This dual functionality is critical for the safe operation of heavy-duty vehicles, as it offers assurance that the vehicle will not inadvertently move while parked or during an unexpected loss of air pressure.

The other options do not accurately represent the primary function of spring brakes. They are not designed for acceleration, regular driving speed control, or towing, which involves different braking or traction systems. Thus, identifying their role as emergency and parking brakes encapsulates their fundamental importance in commercial vehicle safety.