Maryland Transportation Section 22-402
(a)   Every motor vehicle with an internal combustion engine shall be equipped with an exhaust muffler system in good working order and in constant operation to prevent excessive or unusual noise, and no person may use a muffler cutout, bypass, or similar device on a motor vehicle on a highway. Noise levels in excess of those adopted by the Administrator under § 22-601 of this title are excessive.
(b)   A person may not use on the exhaust or "tail pipe" of a motor vehicle any extension or other device to cause excessive or unusual noise.
(c)   (1)   No motor vehicle may be operated, nor may the owner or lessee of a motor vehicle permit it to be operated, on any highway in this State unless the engine power and exhaust mechanism is equipped, adjusted, and operated to prevent:
(i)   The discharge of clearly visible smoke (comparable to smoke equal to or darker in shade than that designated as No. 1 of the Ringelmann Chart as published by the U.S. Bureau of Mines) in the exhaust emissions within the proximity of the exhaust outlet for more than 10 consecutive seconds; and
(ii)   The discharge of smoke from any other part of the engine in such amounts and of such opacity as to partially obscure persons or objects from view.
(2)   In this subsection, "smoke" means small gasborne and airborne particles, exclusive of water vapor, from a process of combustion in sufficient numbers to be observable.
(3)   A motor vehicle engine may not be allowed to operate for more than 5 consecutive minutes when the vehicle is not in motion, except as follows:
(i)   When a vehicle is forced to remain motionless because of traffic conditions or mechanical difficulties over which the operator has no control;
(ii)   When it is necessary to operate heating and cooling or auxiliary equipment installed on the vehicle;
(iii)   To bring the vehicle to the manufacturer's recommended operating temperature; or
(iv)   When it is necessary to accomplish the intended use of the vehicle.
(4)   For a period of 1 year from July 1, 1971, this subsection shall be enforced by issuance of a warning. One year from July 1, 1971, it shall be enforced in the same manner as other violations of this section.
(5)   This subsection does not apply to Class L (historic) vehicles.
(d)   In this section, "muffler" means a device designed for and effective in reducing noise while permitting the flow of gases.
(e)   All mufflers and exhaust pipes carrying exhaust gases from the motor shall be of leakproof construction.