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Loud braking of semis is a nuisance to some, but an important safety feature for truckers

That staccato-like rumbling of big semis trying to slow down reverberates through nearby neighborhoods like thunder and drives some of our viewers nuts.

PORTLAND, Ore. — If you live near a downhill section of freeway, you've no doubt heard that staccato-like rumbling of big semis trying to slow down. It reverberates through nearby neighborhoods like thunder. What’s happening? Engine braking.

"The engine brake was primarily designed for saving your brakes when you're coming down a grade so your brakes don't heat up or they don't heat up as fast," said Patrick Chappell, commercial driver's license (CDL) instructor at Chemeketa College.

Engine brakes, popularly known by the brand name Jake Brake, serve a vital role in transportation safety.

The trademark Jake Brake got its name from Jacobs Manufacturing Company, which started making supplemental engine brakes more than 60 years ago. There's a great story behind that invention, including the tale of a 1931 cross county truck race and a steep hill in California (Cajon Pass) that almost ended in catastrophe. It spotlighted the need to give trucks more braking power.

Video from Jacobs Vehicle Systems shows how the brakes work, ultimately dissipating all the force from the compressed air in an engine "by transforming your power producing diesel engine, into a power absorbing air compressor." That compressed air is released through the exhaust and that’s where the noise comes in — if the truck's exhaust is not properly muffled.

And that brings us to our viewer’s complaint: "Is there a noise ordinance in place during the night that would prohibit this as we are in a residential area close to the freeway?"

The answer is yes. ORS 811.492 states a person commits the offense of engine braking if the person is operating a motor vehicle on a highway and uses an unmuffled engine brake

Credit: KGW

It's not the braking, per se. In fact, some data here from Jacobs — and confirmed by NHTSA — shows that the decibel rating of a truck while engine braking is in line with 1988 EPA noise standards.

However, when unmuffled, those decibel ratings go much higher. Which means it's really a faulty or nonexistent muffler that's the real culprit. Oregon State Police said they've issued 15 warnings in the past decade and suggested it's more of a city noise ordinance thing.  

According to Chappell, engine brakes are installed on the majority of newer trucks and they're a very effective way of slowing a fully loaded semi with 80,000 pounds of goods.

"If I could do it in any other way safely, without putting people's lives in danger, then I probably would," Chappell said.

I do the Driving Me Crazy feature as a generally — but not always — light-hearted take on things that drive people nuts on area roadways. Most of us can relate and most of these topics are your ideas. What drives you crazy? Post your videos and pictures on my Facebook page. On Twitter. Or if you're just anti-social, you can email me at cmcginness@kgw.com.

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