What is the decible level legal for a road legal vehicle. mostly a truck

The police do not go by deibles, concerning the loudness of a truck or car muffler.

There are no set guidelines.

I decide this way......i can live and give a warning to vehicles that have a hole in the muffler and the owner cannot afford to have it repaired right a way. this is a warning and i do not expect to hear this vehicle again. most people comply.

If a muffler is not a stock muffler and installed simply to make noise, i issue a citation. the driver just wants attention.

Truck mufflers are the same way.

If i can hear your vehicle coming from a mile away, your muffler is too loud.

If i cannot hear my police radio in my police car, your muffler is too loud.

If i have a complaint from another citizen about your muffler, i will check it out and act accordingly.

As you can see, the decision is really up the individual officer.

A drivers attitude also plays a big part.

It depends on where you are at.

Are you talking about engine or sound system?

I got ticketed shortly after upgrading my sound system for the first time. Found out that unless you're doing some sort of advertising or public announcements ("Re-elect Mayor Goldie Wilson. Progress is his middle name...") then your music can't be audible 50 feet from the vehicle. That's not very far, even for a stock sound system.

in most states there is no set limit, but most aftermarket exhaust are illegal