1. Definitions. The following words and phrases when used in this section shall have the meanings  respectively assigned to them in this subsection, except where the context otherwise requires.

            a. "dBA" means the composite abbreviation for A-weighted sound level, and the unit of sound level, the decibel.

            b. "Gross combination weight rating" or "GCWR" means the value specified by the manufacturer as the loaded weight of a combination vehicle.

            c. "Gross vehicle weight" means the value specified by the manufacturer as the loaded weight of a single vehicle.

            d. "Sound level" means the A-weighted sound pressure level measured using an instrument complying with the specification for sound level meters of the American National Standards Institute, Inc., or its successor publications, except that only A-weighting and fast dynamic response need be provided.

            e. "Sound level meter" means an instrument or apparatus including a microphone, an amplifier, an output meter, and weighting networks for the measurement of sound pressure.  The output meter reads sound pressure level when properly calibrated, and the instrument is of Type II or better as specified in the American National Standard Institute Publication S1.4-1971, or successor publications.

            f. "Sound pressure level" means twenty times the logarithm to the base 10 of the ratio of the RMS sound pressure to the reference pressure of twenty micropascals (20 x 10-N/M).  The sound pressure level is denoted L or SPL and is expressed in decibels.

    All technical terminology used in this chapter, unless the context otherwise requires, shall be defined in accordance with American National Standards Institute (ANSI) publication S1.1-1960, revised

1971, or successor publications of ANSI, or its successor bodies.

    2. Operating Noise Limits. It shall be unlawful for any person to operate or for the owner to cause or knowingly permit to be operated within this municipality, any motor vehicle which emits a noise sound pressure level in excess of the dB(A) established in this section.  Nor shall any person operate a motor vehicle having a manufacturer's gross vehicle rating of less than ten thousand pounds, except a motorcycle, which exceeds 95 dB(A), measured at least twenty inches from the exhaust outlet.  The measured exhaust system sound level of a stationary motor vehicle shall be the highest reading obtained during the test, disregarding unrelated peaks due to extraneous ambient noise.  When there is more than one exhaust outlet, the reported sound level shall be for the loudest outlet.  When there is more than one outlet extending from a single muffler separated by less than twelve inches, measurement shall not be made on the outlet furthest from the side of the vehicle.

Maximum Allowable Noise Sound Pressure Levels for Motor Vehicles

                    Maximum Allowable    Minimum Measurement

Type of Vehicle                Sound Pressure Level    From Motor Vehicle

Motor vehicles weighing 10,000 pounds    80dB(A)            25 feet

or less, manufacturer's gross vehicle

weight

Motor vehicles weighing more than        88dB(A)            25 feet

10,000 pounds, manufacturer's gross

vehicle weight.

    3. Applicability. This section applies to the total noise from a motor vehicle and shall not be construed as limiting or precluding the enforcement of any other provisions of this chapter relating to motor vehicle mufflers for noise control or violations of Section 10.68.260.

            a. No person shall modify the exhaust system of a motor vehicle or any other noise abatement device of a motor vehicle operated upon the streets and highways of Sioux City in a manner that the noise emitted by the motor vehicle is above that emitted by the vehicle as originally manufactured.  Muffler cutouts, bypasses, or other devices which increase sound emitted shall be considered a violation of this section.

            b. No person shall operate a motor vehicle upon the streets and highways with an exhaust system or noise abatement device so modified.

    4. Exemptions.  The following are exempt from the operation of this chapter:

            a. Noise caused in the performance of emergency work for the immediate safety, health or welfare of the community or individuals of the community or to restore property to a safe condition following a public calamity shall not be subject to the provisions of this chapter.

            b. Construction equipment, street maintenance equipment, and public health and safety equipment.  (Ord. 91/T-10306)