O'Fallon, MO Noise Ordinances: Vehicle Noise (2026)

140(B) prohibits muffler cutouts outright and bars driving any vehicle in a manner or condition that produces excessive and unnecessary noise from its machinery, motor, signaling device, other parts, or an improperly loaded cargo. The provision requires every motor's exhaust to be fitted with a properly attached muffler of sufficient capacity or construction to quiet the maximum possible exhaust noise as completely as is achieved by modern gas engine passenger vehicles, and mandates that any exhaust pipe cutout or opening between the motor and muffler be completely closed, disconnected from its operating lever, and built so it cannot open automatically or be opened while the vehicle is moving.

Subsection (A) of the same section separately addresses horns, requiring every vehicle to carry a working horn or whistle loud enough to warn other road users, but restricting its use strictly to warning purposes; no other sound-producing signaling device may be used at any time, meaning aftermarket horns or noisemakers beyond the required warning horn are barred outright. Both provisions sit within Article II of Chapter 370, Other Vehicle Equipment, alongside separate equipment mandates for brakes, mirrors and load securement. The muffler-cutout ban applies to all motor vehicles operating on O'Fallon streets, including modified exhaust systems installed for performance, since the standard measured is what a stock, properly muffled passenger vehicle achieves.