§7S.  Definitions. 

The following words used in this section twenty-four A to twenty-four C, inclusive, unless the context otherwise requires shall have the following meanings: 

"A-weighted sound level", the sound level in decibels as measured on a sound level meter using a A-weighting network.  The level is designated dB(A). 

"Decibel (dB)", a unit for measuring the volume of a sound, equal to twenty times the logarithm to the base 10 of the ratio of the pressure of the sound measured to the reference pressure; which is 20 micropascals or 20 micronewtons per square meter. 

"Motorcycle", any motor vehicle having a seat or saddle for the use of the rider and designed to travel on not more than three wheels in contact with the ground, including any bicycle with a motor or driving wheel attached, except a tractor or a motor vehicle designed for carrying golf clubs and not more than four persons, an industrial three-wheel truck, or a motor vehicle on which the operator and passengers ride within an enclosed cab. 

"Person", an individual, association, partnership, or corporation, and includes any officer, employee, department, agency or instrumentality of the commonwealth or any political subdivision of the commonwealth. 

"Registrar", the registrar of motor vehicles. 

"Sound level", the weighted sound pressure level obtained by the use of a sound level meter and frequency weighting network, such as A, B or C as specified in American National Standards Institute specifications for sound level meters (ANSI S1.4-1971 or any successor ANSI sound level meter specifications).  If the frequency weighting employed is not indicated, the A-weighting shall apply. 

§7T.  Motorcycle sound levels; testing regulations. 

§7U.  Motorcycles; maximum sound levels. 

No person shall operate any motorcycle intended for use on the highways of the commonwealth and registered under the provisions of section two of chapter ninety which produces a sound level in excess of the following decibels, when measured in accordance with the provisions of the SAE International Recommended Practice SAE J2825, “Measurement of Exhaust Sound Pressure Levels of Stationary On-Highway Motorcycles”:

(a) Ninety-two dBA at idle.

(b) Ninety-six dBA at 2000 (±200) rpm or 75% of maximum engine speed, whichever is less, for motorcycles with less than three cylinders or more than four cylinders.

(c) One hundred dBA at 5000 rpm (±200) rpm or 75% of maximum engine speed, whichever is less, for motorcycles with three or four cylinders.

Before determining compliance, two dBA should be subtracted from the sound measurement for any motorcycle equipped with an exhaust system labeled in accordance with 40 CFR 205.169(e)(1) as meeting the Federal EPA noise emission requirements.  This adjustment shall not apply to labeled systems that have obviously been modified or tampered with.