4. Noise

Question 1

14) What does dB(A) means?

Answer 1

The perceived sound pressure level L is measured in decibels. For traffic noise, the curve “A” is relevant because reduces the sound pressure for low frequencies

Question 2

15) What are the impacts of Noise?

Answer 2

The Damage caused to health:
• from 65 to 75 dB(A): 1- Stress
2- Increased blood pressure
3- Disorders of cardiovascular system 4- Heart attack
• from 85 dB(A):
1- Impairment of hearing
2- For short-time impact, e. g. hammering, temporary hearing threshold shift
3- Long-time or short-time very loud noise impact, e. g. noise exceeding 120 dB(A):
permanent shift of hearing threshold

Question 3

16) What Produce Noise of Road traffic

Answer 3

Vehicle related factors 
• Weight
• Motor capacity
• Motor capacity
• Air drag/ aerodynamics
• Tires
Pavement related factors 
• Type of pavement
• Surface roughness of the pavement
• Pore share of the pavement
Influence of the driving behavior
• Speed 
•Acceleration/deceleration

Question 4

What Produce Noise of Railway

Answer 4

• Motor noise • Aerodynamic noise (relevant for v>300km/h)
• Friction breaks (breaking blocks, disc brakes) • Wheel slippage (curve squealing) • Air conditioning • Vibrations of bogies, axes, tracks

Question 5

What Produce Noise of Aviation

Answer 5

Engines and aerodynamics

Question 6

What are the measures for protection from noise?

Answer 6

1- Protect the “receiver” from the impacts (passive noise protection)
2- Reduction of noise generation at the source (active noise protection)
3- Limit noise propagation (active noise protection):

Question 7

Examples of protection from Noise

Answer 7

Measures on road vehicles
• Silencer (muffler) at the tailpipe 
• Insulation of motors
• Improvements of the air intake 
• Improvement of breaks

Measures on the road pavement
• Avoid too rough surfaces:
a) Cobblestones have the worst performance
b) Double-layer porous asphalt has the best performance
• Placement of drainage installations away from the tire wheel tracks
• Quiet transition between different pavement segments (especially on bridges)

Measures on rail vehicles
• Use of springs and dampers in bogies, axles and vehicle bodies • Reduce roughness of the wheels
• Replace cast iron block breaks by disc brakes
• Optimize size and shape of wheel
• Install bogie skirts

Measures on the track
• Reduce roughness by regular inspection and grinding
• Optimize the stiffness of rubber track pads
• Use rail dampers

Reduction of aviation noise
• Increasing the “Bypass ratio” relation of air that flows around the engine core to the air through the engine core
• Improvement in the aerodynamics of the aircraft to reduce vibrations

a) Noise protection walls
b) Earthdams
c) Trenches and tunnels