CE 453 Lecture 11 : CE 453 Lecture 11 Noise Analysis See: http://www.nonoise.org/library/highway/probresp.htm
and http://www.fhwa.dot.gov/environment/noise/index.htm
and http://www.fhwa.dot.gov/environment/audible/contents.htm
Noise : 2 Noise What is noise?
Who decides? news.bbc.co.uk www.stedmundsbury.gov.uk sprott.physics.wisc.edu/fractals/chaos www.plu.edu/scene/issue/1999/summer/img
Noise : 3 Noise Undesirable or unwanted sound
Subjective
Impacts
Annoyance, disturbance
Stress
Physical and psychological damage
Transportation Noise : 4 Transportation Noise Decreases with increasing distance – a corridor problem
Generated by:
Engine
Exhaust
Aerodynamic friction
Interaction between tire-pavement
Control of Transportation Noise : 5 Control of Transportation Noise Federal -- Noise control act of 1972
Recognized noise as a major degrader of urban living
Encourage use of noise standards
State and local governments
Also institute noise control
Noise Measurement : 6 Noise Measurement Intensity of a single sound is measured on a relative of logarithmic scale
Uses a unit called a bel (B) or subunit – decibel (dB, 1/10 of a bel)
At 14 bels, sound is painful to human ear
Common Sounds : 7 Common Sounds
Noise Propagation : 8 Noise Propagation Noise is generated at source and spreads spherically away from source
Intensity diminishes with distance
Losses also occur from sound energy being dissipated as sound is transferred by air particles
Bending and diffraction occurs as sound waves encounter natural and manufactured solid objects
Noise Control Strategies : 9 Noise Control Strategies Minimize noise levels
Source controls
Vehicle control devices – maintenance, traffic and highway design controls
Path controls
Sound barriers that reflect and diffuse noise
Buffer zones
Receiver-side controls
insulation
Noise abatement measures : 10 Noise abatement measures Traffic management (see next slide)
Buffer zones
Vegetation
Noise insulation
Relocating the highway
Traffic management measures : 11 Traffic management measures Prohibit trucks
Truck routes
Prohibit daytime (or night-time) use
Traffic signal timing
Speed limits
Will all these work?
Slide12 : 12 http://www.nonoise.org/library/highway/traffic/traffic.htm Noise
Source
Slide13 : 13 http://www.nonoise.org/library/highway/traffic/traffic.htm
Slide14 : 14
Slide15 : 15 http://www.nonoise.org/library/highway/traffic/traffic.htm Paths:
Effects of distance
And adding sources
Slide16 : 16 http://www.nonoise.org/library/highway/traffic/traffic.htm Receivers:
Perceptions
of noise
Slide17 : 17 Number of people annoyed
At different sound levels
Slide18 : 18 http://www.nonoise.org/library/highway/policy.htm
Slide19 : 19
Slide20 : 20
Noise Measurement : 21 Noise Measurement Significant variability in noises from transportation sources
Lp: noise level at a particular receptor that is exceeded p percent of the time
i.e. Noise that exceeds 100 db 90% of the time
A-weighted noise level (equivalent “irritation” level – has to do with mix of frequencies
DNL (day/night level – weights nighttime noises)
What are L10 and Leq? : 22 http://www.nonoise.org/library/highway/policy.htm#II What are L10 and Leq? The equivalent sound level is the steady- state, A-weighted sound level which contains the same amount of acoustic energy as the actual time-varying, A-weighted sound level over a specified period of time. If the time period is 1 hour, the descriptor is the hourly equivalent sound level, Leq(h), which is widely used by SHAs as a descriptor of traffic noise. An additional descriptor, which is sometimes used, is the L10. This is simply the A-weighted sound level that is exceeded 10 percent of the time.
What are L10 and Leq? : 23 http://www.nonoise.org/library/highway/traffic/traffic.htm What are L10 and Leq? L10 is usually about 3dB greater than Leq
Mathematical Model : 24 Mathematical Model Simple model
L50 = 68 + 8.5 log V – 20 log D (db)
Where:
V = traffic volume (veh/hour)
D = distance from traffic to observer in feet
Also use nomographs, relate noise to speed, volume, distance, etc.
State of the Art is FHWA’s Traffic Noise Model (TNM) : 25 State of the Art is FHWA’s Traffic Noise Model (TNM)
Modeling of five standard vehicle types, including automobiles, medium trucks, heavy trucks, buses, and motorcycles, as well as user-defined vehicles.
Modeling of both constant-flow and interrupted-flow traffic using a 1994/1995 field-measured data base.
Modeling of the effects of different pavement types, as well as the effects of graded roadways.
Sound level computations based on a one-third octave-band data base and algorithms.
Graphically-interactive noise barrier design and optimization.
Attenuation over/through rows of buildings and dense vegetation.
Multiple diffraction analysis.
Parallel barrier analysis.
Contour analysis, including sound level contours, barrier insertion loss contours, and sound-level difference contours.
Slide26 : 26 2280 120 60 Problem: Find dBA L10
500 ft from road
2 lane road
2400 vehicles per hour
5 percent trucks
60 mph
#cars = .95x2400=2280 Example Problem
Slide27 : 27 Problem: Find dBA L10 at 500 ft
From a 2 lane road carrying:
2400 vehicles per hour
5 percent trucks, at
60 mph … cars = .95x2400=2280
L50 dBA for cars at 100’ = 68 dBA
Slide28 : 28 68 2280 120 60
Slide29 : 29 Problem: Find dBA L10 at 500 ft
From a 2 lane road carrying:
2400 vehicles per hour
5 percent trucks, at
60 mph … trucks = .05x2400=120
L50 dBA for trucks at 100’ = 62 dBA 20
30
40
50
60
70
Slide30 : 30 68 62 2280 120 60
Slide31 : 31 Problem: Find dBA L10 at 500 ft
From a 2 lane road carrying:
2400 vehicles per hour
5 percent trucks, at
60 mph …
O-ELD = 500’
Slide32 : 32 Problem: Find dBA L10 at 500 ft
From a road carrying:
2400 vehicles per hour
5 percent trucks, at
60 mph …
Adjustment from 100ft ref = -10 dB
Slide33 : 33 68 62 -10 -10 2280 120 60
Slide34 : 34 Problem: Find dBA L10 at 500 ft
From a road carrying:
2400 vehicles per hour
5 percent trucks, at
60 mph … (vol/speed)*ELD = 19,000 for cars, 1,000 for trucks
L10 - L50 = 2 dBA cars, 6.5 dBA trucks
Slide35 : 35 68 62 -10 -10 2 6.5 60 58.5 60 58.5 2280 120 60
Slide36 : 36 Adding 2 sources Heavy trucks 58.5 db
Passenger vehicles 60 db
Slide37 : 37 Difference = 60 – 58.5 = 1.5
Add 2.3 db to higher
60 + 2.3 = 62.3 db due to both sources
Slide38 : 38 68 62 -10 -10 2 6.5 60 58.5 60 58.5 62.3 2280 120 60
Slide39 : 39
Slide40 : 40
Slide41 : 41
Noise Barriers : 42 Noise Barriers
Other Adjustments : 43 Other Adjustments Grade (trucks)
+/- 3-4% = +2
+/- 5-6% = +3
+/- >7 = +5
Surface
very smooth = -5 (auto only)
very rough = +5
(auto, or truck>60mph) Interrupted flow (L10)
auto = +2
Truck = +4
Foliage
-5 for each 100’ >15’
-10 max
Rows of houses
-5 for each
-10 max
Noise Barriers (how they work) : 44 Noise Barriers (how they work) Noise is "diffracted" over the barrier, this increases the distance it travel to the listener, thus decreasing the noise A + B > C Source:http://www.urbislighting.com/uap1.html
Slide45 : 45 Source: FHWA, “Keeping the Noise Down, Highway Traffic Noise Barriers”
Noise Barriers (how they work) : 46 Noise Barriers (how they work) Noise is also reflected and/or absorbed Source:http://www.urbislighting.com/uap1.html
Possible barriers : 47 http://www.nonoise.org/library/highway/traffic/traffic.htm Possible barriers
Slide48 : 48 http://www.nonoise.org/library/highway/traffic/traffic.htm
Slide49 : 49 Source: FHWA, “Keeping the Noise Down, Highway Traffic Noise Barriers”
Slide50 : 50 Source: FHWA, “Keeping the Noise Down, Highway Traffic Noise Barriers”
Slide51 : 51 Source: FHWA, “Keeping the Noise Down, Highway Traffic Noise Barriers”
Slide52 : 52 Source: FHWA, “Keeping the Noise Down, Highway Traffic Noise Barriers”
Slide53 : 53 Source: FHWA, “Keeping the Noise Down, Highway Traffic Noise Barriers”
Slide54 : 54 Source: FHWA, “Keeping the Noise Down, Highway Traffic Noise Barriers”