What is the reason for the sound we hear during bus journeys, especially at night, that makes us sleepy as if we were in our mother’s arms?

Especially during long night journeys, when we lean our heads against the bus window in a slightly groggy state, we hear a humming sound, and this sound strangely gives us peace. We fall asleep while the sound is ringing in our ears.

There are even 1-hour videos on YouTube with only this sound. We don’t know if you’ve ever questioned what the sound is, but if it aroused curiosity in your mind when you read the title, let’s take you into the details of the content.

Let us remind you for those who do not understand the sound:

The operating principles and parts of private cars and large vehicles such as buses and trucks are generally different from each other.

automobile brake system

If we give an example of the difference between small cars and buses; While trucks generally use special braking systems to control heavy loads, small cars use standard braking systems.

The reason for the sound we hear only on bus trips, not in our private vehicles, is actually due to such a difference.

When we understand the difference between the brake systems in buses and small vehicles, we will also learn the source of the hum.

retarder

As we just mentioned, since cars have a lower weight than buses, a relatively easier braking system using disc or drum is used. Vehicles such as trucks or buses also have different braking systems as “primary” and “secondary”.

The system we call “primary” actually works on the principle of friction between the pads and brake disc, just like in our cars. The system we call “secondary” includes exhaust brake, engine brake and hydraulic retarder, etc. covering systems. These secondary braking systems are called retarders.

So what is this retarder and what does it do?

The sound we hear on buses, which creates an “ASMR” effect and puts us to sleep, means that the retarder is working. The retarder, which provides deceleration, supports the braking ability in a way. In fact, the origin of the word means “slowing down”.

We can also explain it this way; They reduce wear and extra costs by ensuring less use of brake pads, provide safety by preventing the risk of brake discharge when descending steep slopes, and since the intensity can be adjusted by the driver, they can also adjust the torque control at different levels.

Now that you know the source of the sound, you can fall into a more peaceful sleep by listening to the humming sound…

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