CE 561 Lecture Notes. Reference, AASHTO, Guide on Evaluation and Abatement of Traffic Noise, Set 9. General Characteristics

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1 CE 561 Lecture Notes Set 9 Reference, AASHTO, Guide on Evaluation and Abatement of Traffic Noise, 1993 General Characteristics Noise an unwarranted or excessive sound a form of environmental degradation Sound sensation produced by air waves created by vibrational disturbance Unshielded Dwelling Shadow Zone Shielded Dwelling Noise Barrier Road The acoustic energy in the wave decreases in proportion to the square of the distance from the source. Noise Barrier - abating effect

2 Measures of Sound Intensity Loudness or intensity related to the amplitude of hearing 2 x 10-5 Newtons/sq.m Threshold of pain 63 x 10-5 Newtons/sq.m Decibel (db) is a term borrowed from electrical communications engineering, representing a relative quantity Sound Pr essure Level (db) p p p0 2 = 10log ( 2 10 N/ ) 0 = reference pressure m p = sound pressure of SPL concern If the sound pressure is increased by a factor of 2, an increase in the sound level would be 3 db 10log 102 = 3 Decibels do not add in a linear fashion, but logarithmically. SPL / 10 ( db) = 10log Σ total Example: Given 2 sources 64 and 60 db 65 Combined db 10 10log 10 + = 10 x = db 60 = In outdoor, a change > 3 db is required to be noticeable. A change of 10 db is generally perceived to be a doubling of the sound level. The range of SPL associated with traffic related noise is db

3 Frequency Number of times a sound wave repeats itself in each second. 1 Hertz is one cycle per second. The audible range is from 20 to 20,000Hz. Fluctuations in Traffic Noise Max sound level, L max (t) e.g. 60 db, L max (1 hour) Statistical sound levels, L xx (t) the p.c. of time that the listed level is exceeded during t. A reported 60 db as L 10 (1 hr) would mean that 60 db was exceeded 10% of the time in a one-hour period. L 10, L 50, L 90 commonly used. Leq, the equivalent SPL N 1 ( L ) t /10 = 10log10 Σ 10 T t= 1 L t = sound level in dba T = total time t = increment of time Leq indicates mean level over a specified period during which the sound level fluctuated.

4 Sound Level Change 0 dba Acoustic Energy Loss 0 50% 90% 99% 99.9% 99.99% Relative Loudness Reference Perceptible Change Half as Loud ¼ as Loud 1/8 as Loud 1/16 as loud The noise level will decrease from 3 to 4.5 dba for each doubling of distance from the source, depending upon the absorptive characteristics of the ground. Noise Effects Health Effects Physiological Increases in blood pressure, heart rate and breathing Psychological Psychiatric Disorders Effects on Sleep Physiological Effects Feeling of Annoyance Indirect Effect on Performance Effects on Communication Masking of desired sounds Loss of information caused by noise interference could be dangerous in cases where it masks Auditory warning The malfunction of equipment Approach of vehicles Reduce quality of teaching Adversely affect the ability of children to learn

5 Effects on Performance Distract a person involved in a specific task Change state of alertness Tasks involving high concentration, vigilance, mental activity and high complexity affected adversely Annoyance Effects Depends on individual s personality, social habits, psychological state Legislations and Regulations Housing and Urban Development Act of 1965 Noise Control Act of 1972 urban noise control Control and Abatement of Aircraft Noise and Sound Boom Act of 1968 Quiet Communities Act of 1978 Better defined and added to Noise Control Act A desirable neighborhood goal of 55 dba FHWA has defined procedures (23 CFR 772) that must be followed to predict the worst hour noise levels Trucks (heavy diesel powered) present the most difficult noise problem 15 dba higher than autos Noise Control Program Compatible land use Facility location and design Construction noise

6 Traffic Noise Control Noise Control at Source, Including the Removal of Vehicles and Re-Routing Vehicle noise control Engine and exhaust Fan noise Transmission Tire/roadway surface interaction Aerodynamic noise Chassis and load vibration Brake squeal Roadway design and alignment grades, stops, sharp curves, pavement type, expansion joints Temporal and geographical restrictions of noisy heavy vehicles Noise Control of the Transmission Path Construction of noise barriers Use of vegetation Use of natural landform The Use of Noise Protective Measures at the Receiver Sound insulation of sensitive buildings Retrofitting existing buildings Modification of construction codes for new developments Land use controls for compatible development Methods of Prediction Manual methods (formulae or nomograms) NCHRP short method Computer programs Stamina Barrier cost reduction (BCR)/Optima (combines Stamina with an integrating economic analysis program)

7 Overall Noise Impact Analysis Framework Identify locations that will be affected by changes in noise levels Identify activities at impacted locations Compute noise levels and change in noise levels at locations affect by project development Present Future Assess noise effects/impacts by activity type (e.g. houses, schools, offices, churches, etc.) Magnitude and extent Consider mitigation measures Perform cost-effective analysis Energy Impacts Total U.S. Energy Consumption by Sector (1999) Transportation 26% Industry 36% Residential/Commercial 35% Transportation s share has been steadily increasing (in 1980 it was 20%) Transportation energy use by mode (1998) Air 8% Pipeline 3% Water 5% Rail 2% Transit 1% Heavy Duty Trucks and Buses 18% Light Duty Vehicles 63% Highway vehicles account for about 80% of transportation energy use. Passenger cars 42% of the sector s total

8 Energy Use Vehicle operation Facility construction, maintenance, and operation Vehicle manufacturing and maintenance Secondary effects due to relocation of activities Vehicle Operation Energy Use Amount of travel Modal shifts Vehicle occupancies Fuel economies Societal/Economic Costs Average Energy Consumption Rates (1998) Automobiles 3700 btus/passenger mile Transit 4100 Intercity 900 Rail 3100 Amtrak 2500 Air 4000 Congestion and Fuel Consumption FC = C VM VM + C CD CD FC = Change in fuel consumption in gallons VM = Change in VMT CD = Change in congestion delay in vehicle-hours

9 C VM (gals. per vehicle-mile) C CD (gals. per hr. of delay) Automobiles Heavy Trucks Buses