What do mufflers in a vehicle control?

Mufflers play a critical role in a vehicle's exhaust system primarily by controlling emissions and noise emitted from the engine. Their primary function is to reduce the sound produced by the exhaust gases as they exit the engine and pass through the exhaust system. This reduction in noise is crucial for meeting regulatory standards for vehicle noise and for providing a more pleasant driving experience.

Additionally, mufflers help in managing emissions by aiding in the proper expulsion of exhaust gases from the engine, which can also have implications for vehicle performance and compliance with environmental regulations. Through various design features, they can assist in quieting the sound while allowing exhaust gases to exit effectively, thereby ensuring that the vehicle operates within acceptable noise and emission levels.

The other options are related to different vehicle systems and functions. For instance, the speed of the vehicle is determined by the engine power and transmission, the temperature of the engine is controlled by the cooling system, and the brakes are part of the braking system. Each of these systems serves distinct purposes that are not related to the muffler's functions.