Truckers: Modified Exhaust Systems Prohibited

Every day on the way to work, I pass by a sign that says:

“Truckers: Modified Exhaust Systems Prohibited”

At first I thought they were talking about something like Jake Brakes, but those are usually either called Jake Brakes or Engine Brakes on signs. So what exactly is this referring to?

This sign is on Maryland Rt. 30, in between Hampstead and Owings Mills, if the location (or at least the state) matters.

Most big diesel engines have an exhaust system with a catalyst chamber that removes a lot of the pollutants from the exhaust stream (primarily, sulfur, IIRC). These are expensive to regenerate when they are full, and especially in older designs, reduce engine performance quite a bit.

Some drivers would either bypass the restrictive portions of the exhaust system, or simply open them up, which causes emissions to go through the roof.

The sulfur collection systems are still in use, but are becoming less and less necessary as almost all diesel fuel sold now has a very low sulfur content from the refinery.

And I’m not surprised that this would be in MD, where emissions are a big deal.

Along with the emissions as Khendrask mentioned, it is also somewhat “fashionable” to run straight stacks, meaning no muffler. You can imagine how loud this is. Then throw the Jake Brake switch and you can knock little birds out of the trees. I would bet if its a residential area this is the case. As of 2007 diesel trucks (pickups also) coming off the assembly line have to meet much more stringent emission standards, and the diesel fuel also had to go from 500 ppm to 15 ppm sulfur content. If you watch a recent episode of Sliced you will see the guy open up one of the catalyst chambers that Khendrask mentioned. I wouldn’t say its impossible but bypassing one of these systems would be very difficult. On the plus side they say you can breath the exhaust coming out of one of these trucks and its cleaner than the air you would breath in down town Seattle.