THE SCIENCE AND APPLICATIONS OF ACOUSTICS - H. H. Arnold ...

Highway Construction Noise13.10 Evaluation of Traffic Noise 339No specific quantitative rules or guidelines for limiting highway construction noiseare provided by the FHWA, but some state agencies use the criteria of Table 13.3as guidelines for assessing the impact of construction. However, a computer model(HICNOM) is available from FHWA to be used to predict construction noise andasses abatement measures.Vehicle NoiseMajor contributors to vehicle noise include the engine exhaust and air intake, engineradiation, fans and auxiliary equipment, and tires. To a lesser degree othernoise sources are the transmission, driving axles, and aerodynamic noise due tothe passage of the vehicle through air. The relative importance of each componentdepends on the vehicle type and condition, vehicle load (passenger and cargo),speed, acceleration, and highway grade, and road surface condition. In order toaid in prediction of highway noise, FHWA conducted an exhaustive series of measurementsof noise emission from, automobiles, trucks, buses, and motorcycles.The procedure for determining the noise emission levels entails the followingsteps:1. A level open space free of large reflecting surfaces within 30 m (100 ft) of thevehicle path or microphone is identified. A 150 ◦ clear line-of-sight arc from themicrophone position is required.2. The surface of the ground should be free of snow and may be hard or soft.The roadway should be relatively level, smooth, dry concrete or asphalt. Thereshould be no gravel.3. The background level from all sources except the vehicle in question should beat least 10 dB(A) lower than the level of the vehicle in question.4. The microphone is situated 15 m (50 ft) from the centerline of the lane of travel.5. The microphone is mounted 1.5 m (5 ft) above the roadway surface and notless than 1 m (3.5 ft) above the surface upon which the microphone stands. Itshould be oriented according to the manufacturer’s specifications.6. The vehicle in question should be traveling at steady speed without accelerationor deceleration.Vehicles are grouped by FHWA into three classes:1. Automobiles (A): All vehicles with two axles and four wheels, including automobilesdesigned for transportation of nine passengers or fewer, and lighttrucks and SUVs. Generally, the gross vehicle weight (GVW) is less than 4500kg (10,000 lb).2. Medium Trucks (MT): All vehicles having two axles and six wheels, generallyin the weight class 4500 kg (10,000 lb) GVW 12,000 kg (26,000 lb).