Noise Pollution Emitted by Transportation Systems

Author: Dr. Jean-Paul Rodrigue

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1. Road Transportation Noise

• Road accounts for approximately 70% of total noise emissions by transportation. It must be noted that different road transportation modes have different scales of noise emissions.
• Main sources of noise come from the engine and the friction of the wheels over the road surface. Further, travel speed and the intensity of traffic are directly linked with its intensity of noise. For instance, one truck moving at 90 km/hr makes as much noise as 28 cars moving at the same speed.
• Ambient noise is a frequent result of road transportation in urban areas. The addition of all the noise generated by cars, trucks and buses creates a permanent ambient noise (ranging from 45 to 65 db) that impairs the quality of life in urban areas and thus the property values of residences. Nearby road arterials, ambient noise is replaced by direct noise and vibrations. The acoustics created by the surrounding environment (hills, buildings, trees, open space, etc.) alleviate or worsen local conditions.
• Noise level grows arithmetically with speed. For instance a car traveling at 20 km/hr emits 55 db of rolling noise, at 40 km/hr 65 db, at 80 km/hr 75 db and at 100 km/hr 80 db. Available evidence underlines that around 45% of the population in developed countries live in high levels of noise intensity (over 55 db) generated by road transportation. Along major highway arterials in inter-urban areas, noise emissions are likely to alter the living environment of wildlife species.

2. Rail Transportation Noise

• Rail accounts for 10% of total noise emissions by transportation. Noise comes from the engine (mostly diesel), the friction of wheels over the rails, and whistle blowing. Furthermore, when trains are moving at high speed, areoacoustic noise becomes more important than other sources. Depending of the train aerodynamics, noise emissions are from 50 to 80 times the logarithm of train speed and become significant at speeds higher than 200 km/hr.
• When rail / truck transshipment is involved, the convergence of trucks towards railyards provides an additional source of noise related to rail transportation activities.
• Around 3% of the population may be exposed to high noise levels from rail transportation in OECD countries. The level of exposure is obviously related to the importance and location of rail transportation infrastructure. The most important noise impacts of rail operations are in urban areas where the majority transshipment functions are performed. Furthermore, rail terminals are often located in the central and high density areas of cities.

3. Air Transportation Noise

• Air transportation accounts for 20% of total noise emissions by transportation. As air transportation took a growing importance in inter-city transportation and that jet engines were predominantly used, noise emissions have increased significantly to the point of becoming a major concern near airports.
• Noise comes from the jet engine, the aerodynamic friction and ground craft operations. Even if the turbofan is the least noisy jet propulsion technology available, aircrafts are an acute source of noise in several urban areas. Noise from aircraft operation is known to have direct impact on property values around airports. This effect is distributed along major approach and takeoff lanes.
• The establishment of heavily used flight paths between major cities creates noise corridors where ambient noise is almost prevalent. This is particularly noted when those corridors are over densely populated areas.