Chapter 07. Noise Abatement Program

“dB(A)” means the accepted abbreviation for A-weighted sound level in decibels.

“GCWR” means gross combination weight rating.

“GVWR” means gross vehicle weight rating.

“Ground cover” means any various low, dense growing plants, such as ivy, myrtle, low weeds, or brush.

“Hard test site” means any test site having the ground surface covered with concrete, asphalt, packed dirt, gravel, or similar reflective material for more than 1/2 the distance between the microphone target point and the microphone location point.

Highway.

“ISO” means the International Organization for Standardization.

“Lmax” means maximum sound level measurement.

“SAE” means Society of Automotive Engineers, Inc., or its successor bodies.

“Soft test site” means any test site having the ground surface covered with grass, other ground cover, or similar absorptive material for 1/2 or more of the distance between the microphone target and the microphone location point.

“Sound level” means the A-weighted sound level obtained by the use of fast meter response and A-weighting characteristic specified in American National Standard S1.4—1971 “Specification for Sound Level Meters.”

Motor vehicle while in motion;

Stationary motor vehicle equipped with an engine governor; and

Stationary motor vehicle without an engine governor.

The sound generated by a horn or other warning device when operated under the provisions of the Transportation Article, §22-401, Annotated Code of Maryland;

The sound generated by an emergency motor vehicle when operating under the provisions of the Transportation Article, §22-106, Annotated Code of Maryland;

The sound generated by transit and school buses.

Measurement shall be made at a measurement site which is adjacent to, and includes, a portion of a traveled lane of a public highway. A microphone target point shall be established on the centerline of the traveled lane of the highway and a microphone location point shall be established on the ground surface 50 feet (15.2m) from the microphone target point. Within the site is a triangular measurement area. A plan view diagram of a standard site, having an open site within a 50 foot radius (15.2m) of both the microphone target point and the microphone location point, is shown in Figure 1.

The sound level generated by the motor vehicle is the highest reading observed on the sound level measurement system as the vehicle passes through the measurement site. The sound level of the vehicle being measured shall be observed to rise at least 6 dB(A) before the maximum sound level occurs and to fall at least 6 dB(A) after the maximum sound level occurs.

Standard Measurement Site Highway Operations.

The motor vehicle to be tested shall be parked on a flat open area free of acoustically reflective surfaces (except those of the vehicle under test) that are within 15 feet of the microphone measuring position. See Figure 2 for microphone orientation. Before starting the sound level measurement, the vehicle engine should be at normal operating temperature.

The microphone shall be located at a height equal to that of the exhaust discharge opening (but not less than 1 foot from the ground) and shall be positioned 3 feet from the exhaust opening with the microphone in a vertical or a grazing position and as far as possible from any acoustically reflective surfaces associated with the vehicle being tested, the inspecting officer, or the associated testing equipment. See Figure 2.

All auxiliary equipment such as cranes, asphalt spreaders, liquid or slurry pumps, auxiliary air compressors, welders or trash compactors, which are installed on the motor vehicle and which are designed to operate under normal conditions when the vehicle is operating at a speed of 5 miles per hour (8 kph) or less, shall be turned off.

If the motor vehicle engine radiator fan drive is equipped with a clutch or similar device that automatically reduces the rotational speed of the fan or completely disengages the fan from its power source in response to reduced engine cooling loads, park the vehicle before testing with the engine running at high idle or any other speed the operator may choose, for sufficient time but not more than 10 minutes, to permit the radiator fan to automatically disengage.

Stationary measurements require that the microphone be located 3 feet from the vehicle exhaust opening, as shown in Figure 2. There shall be no acoustically reflective objects closer than 15 feet to the microphone measuring position except those of the vehicle under test, the inspecting officer, and the associated testing equipment.

Standard Measurement Site Stationary Operations.

A motor vehicle with a manual transmission shall be in neutral and the clutch engaged. A motor vehicle with an automatic transmissions shall be in park or in neutral.

With the compression brake engaged (if the vehicle is so equipped) and the engine at idle, the sound level measurement shall be started. Then, the throttle shall be rapidly depressed to wide open and returned to idle speed. This procedure is repeated for a total of 3 engine run-ups during the measurement period. For vehicles without an engine speed governor, the engine shall be accelerated to approximately one-half throttle.

If the motor vehicle is equipped with dual exhausts, these procedures shall be applied to both sides of the motor vehicle.

If all 3 engine run-up maximum sound level measurements exceed the maximum permitted level specified in Table 3 for the category of the vehicle under test, a noise violation exists. This test procedure may be repeated if deemed necessary by the inspecting officer.

The measurement site shall be an open site, essentially free of large sound reflecting objects and not closer than 200 feet between the microphone target point and a tunnel or underpass.

The following objects may be within the site including the triangular measurement area:

The following objects may be within the measurement site if they are outside of the triangular measurement area of the site:

Holes or other defects which would cause a vehicle to emit irregular tire, body, or chassis impact noise; and

Loose material such as gravel or sand.

Sound. The ambient A-weighted sound level at the microphone location point may be measured, in the absence of motor vehicle noise emanating from within the clear zone, with fast meter response using a sound level measurement system that conforms to Regulation .10 of this chapter.

The measured ambient sound level shall be 10 dB(A) or more below that level specified in Regulation .04 of this chapter, Table 1, 2, or 3, which corresponds to the maximum permissible sound level reading which is applicable at the test site at the time of measurement.

Ambient sound levels need not be taken when a:

Wind. The wind velocity at the site may be measured at the beginning of each series of noise measurements and at intervals of 5—15 minutes thereafter until it has been established that the wind velocity is essentially constant. Once this fact has been established, wind velocity measurements may be made at hourly intervals. Testing can be done if velocity is 12 mph (19.3kph) or less, but gust winds up to 20 mph (33.2kph) are allowed.

Precipitation. Measurements are prohibited under any conditions of precipitation; however, measurements may be made with snow on the ground. The ground surface within the measurement area shall be free of standing water.

Measurements made at sites with sound reflecting surfaces located behind the microphone line or beyond the vehicle fore and aft center line and outside the triangular measurement area shall be adjusted by the factors in Table 4. If the reflecting surfaces are both behind the microphone and beyond the vehicle, they are additive. Measurements may not be made when a sound reflecting surface is less than 25 feet from the microphone or vehicle or when there are more than two reflecting surfaces within a site.

Tables. The following tables are used for noise measurement site adjustments:

An acoustical calibrator of the microphone coupler-type shall be used for calibration of the sound level meter. The frequency of the calibration signal shall be 1000 Hz, ±5 percent.

The calibrator shall be adjusted and certified annually with a method traceable to the U.S. National Bureau of Standards to verify its correct performance within ±0.5 dB.

A windscreen of the type recommended by noise meter manufacturers shall be used for all measurements to protect from wind noise. Installation of the windscreen may not cause a change in the sensitivity of more than ±.05 dB in the frequency range from 50 Hz to 5KHz or more then ±2 dB in the frequency range from 5 KHz.

It is sufficient that this compliance be demonstrated only at the annual system calibration and certification.

10,000 or less GVWR or GCWR. The same procedures as described in Regulation .05B of this chapter are used.

Motorcycles. The same procedure as described in Regulation .05B of this chapter are used.

The sound level meter shall be operated according to the manufacturer's instructions and this section.

The meter shall be set for A-weighting and fast response.

The sound level meter shall be calibrated with the acoustic calibrator before the start of use and then at approximately 1 hour intervals when the instrument is in use.

The operator may not stand at any point in the measurement site that lies on a line passing through the vehicle and the microphone. An operator, witness, or trainee may be positioned behind the microphone but no closer than 2 feet from the microphone.

Background Sound Level. The sound level, including that from other vehicles, wind effects, and all other sources of noise except the vehicle being measured, shall be at least 10 dB lower than the maximum sound level of the vehicle at the time of the measurement.

Meter Reading. The sound level reading of a moving vehicle or a stationary vehicle shall be at the highest reading observed for each measurement period.

Location of measurement site and posted speed, if applicable;

Date and time of day of the measurements;

Name of operator making the measurements;

Identifying numbers of measurement equipment; and

For every violation observed, a description of vehicle, the lane of operation (except for stationary vehicle measurements), the sound level reading as defined in this chapter, the maximum permitted sound level, the time, the enforcement action taken if any, wind speed, calibration times, and any other information deemed necessary.

The Administration considers ISO 5130 1982 E and SAE standards and recommended practices to contain minimum requirements. In conducting tests in compliance with these procedures, the Administration may deviate from the literal requirements when it appears that the integrity of the test methods can be better preserved.

Using instrumentation having greater precision or adding additional equipment to provide more accuracy in determining test conditions, and reducing the presence of objects in the test zone are examples of deviations from the referenced texts.

The appendices attached to the referenced texts contain recommended sound level limits that are not appropriate to this regulation and are therefore deleted.

Filed annually;

Filed before the date of introduction of a new model; and

Accompanied by a list of models of the same model year that are available outside of this State that do not comply with the provisions of this chapter.