Should You Be Worried About ‘No Engine Brakes’ Signs?

So you were driving along a two-lane road on the outskirts of a city that day, when you saw a sign posted at the city limits: “NO ENGINE BRAKE.” Naturally, I wondered what the rule meant and whether it applied to you. The truth is, engine braking is a great semi-use diesel vehicles technology to slow down. Because these “”s can be so loud, many cities have laws preventing their use.

What is the engine braking system?

Engine brake sign | 6 WOWT News via YouTube

A diesel engine’s braking system—also called a pressure-release brake, decompression brake, or jake brake—converts the vehicle’s forward momentum into engine pressure, and then releases that pressure through the exhaust valves.

And a gasoline engine. When you take your foot off the accelerator in a gas-powered car, its engine stops sucking air into its cylinders. But the diesel engine does not have it, so air continues to flow into its cylinders. If the engine is connected to the drivetrain, this air is compressed, and then pushes the vehicle forward while decompressing.

The pressure release brake simply releases this compressed air before it can create torque and propel the vehicle forward.

Why do truck drivers use engine brakes?

A semi-truck uses engine brakes to stop on a deserted highway.
Semi truck on a highway | Jacob Borzycki/NourPhoto

Truck drivers use the engine brakes to slow their vehicles while saving the wear of the hydraulic braking system.

Most pressure-release engine braking systems are fully configurable: the driver can select the number of engine cylinders to be activated, thus adjusting the braking intensity. The driver can also select a gear to adjust the brakes further, then release the gas and clutch and let the engine brake slow the truck.

Some of the commenters here on MotorBiscuit claim to be truckers and admit that they also enjoy the sound of a loud engine brake, just as much as they enjoy a loud diesel engine. People who enjoy the experience of driving a semi truck will obviously be the ones who are drawn to this important profession.

Why is engine braking illegal in some places?

A semi-truck driving in a residential area does not allow engine brakes
semi truck in town | Robert Nickelsberg/Getty Images

Because the truck’s semi-compact version engine brakes can be quite loud, many municipalities have laws that prevent their use. But modern mufflers can quiet down engine brakes—according to. So some towns only ban “unmuffled” engine brakes.

Engine brakes have a bad reputation. This is probably because many semi-trucks in the past had unmuffled engine brakes in residential areas. Outraged homeowners drafted ordinances against them, and in many places engine brakes are now outlawed.

But most truck drivers avoid using the engine brake in cities, even when they are allowed to do so. Others have done a great job of putting out the pressure release motor brake so they can use it without bothering anyone.

Then, find out why some engine brake-inspired road rage crashes happen or watch in this latest video:

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