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Summary of Initial Train Noise Study
China Project - Shenzhen 2/28/2000
Sephir Hamilton


Recommendations

  1. Install continuous traffic barrier near train tracks.
  2. Use heavy wall construction with no openings or seams.
  3. Use heavy-paned, non-opening, double-glazed windows (at least 3" air space).
  4. Seal all cracks, joints, and discontinuities in the wall (especially window mounts).
  5. Minimize the wall (flat wall) and window areas (small windows) on the exposed side.
  6. Build a continuous structure adjacent to the tracks to block the rest of the site (taller is better).
  7. Situate bedrooms on "quiet-side," living and dining rooms in the middle, and kitchen/bath and common areas on the exposed side.
  8. Place no vents or other openings through the exposed wall.

Explanations
Trains are noisy. People expect privacy in their homes. When a person's home is near a railway, he can not expect acoustic privacy unless good design, planning, and construction blocks the noise from reaching his home. Since trains produce about 90-100 dB(A) (measured at 15m) and people permit only up to 35-45 dB(A) in their homes the noise must be cut by about 55 dB(A). In terms of energy, 99.9997% of the noise must be blocked before it enters the home to get the required noise reduction.

There are several accepted methods for reducing transportation noise in buildings. The first, and most effective, method for reducing transportation noise is to reduce the noise source. For a train this means, adding exhaust mufflers to locomotives, replacing butt-end track with welded track, and balancing freight-car wheels. This analysis assumes that this method will not be achieved in Shenzhen.

A more widely used method for reducing transportation noise in buildings is to block the noise path with barriers. This brief analysis focuses on eight construction recommendations that, when properly implemented, can block enough train noise to maintain acceptable noise levels in homes. Note, however, that it will be practically impossible to block all train noise in a building next to a railway. More detailed analysis will soon be necessary to ensure that noise is blocked at all needed frequencies for a given construction. This initial analysis is a tool for designers as they plan the site.

1. Traffic Barrier Barriers
are often used on highways to reduce road noise as heard by adjacent homes. The barriers can also be installed near a railway to block up to 10 or 15 dB(A) of noise. The USDOT Traffic Barrier Design Handbook should be used to design a proper barrier for the Shenzhen site. Key design points of proper barrier design are:

  • The barrier must extend well past the sound protected area (about 50% of the perpendicular depth of the area) in both directions parallel to the train tracks. It would be very advantageous to extend a continuous barrier the entire length of the "Wonderland" development (even the areas already developed).
  • The height of the barrier must be at least tall enough to block the line-of-sight between the top of the tallest building on the site and the train. Diffraction over the barrier means that apartments on upper floors will have more sound exposure than lower apartments.
  • Earth berms (built-up mounds of earth) can be used instead of or in combination with typical masonry barriers. · The barrier must be continuous throughout its length (no openings or breaks).

2. Heavy Wall Construction (exposed wall only)
Thick massive exterior walls will best block the outdoor noise from entering a building. A wall should be designed and built to give a minimum STC rating of 55 (one can imagine the STC rating to be approximately the noise reduction in dB(A)). A more detailed look at the frequency response of materials will show exactly what materials will work for train noise (which has more low-frequency noise than high-frequency noise). Thick concrete, brick, or other solid and continuous materials would be appropriate.

3. Heavy Double Windows (exposed windows only)
The windows of a building are usually the weakest link in noise reduction construction. Typical single-paned windows only have an STC rating of 20 or so. Double-glazed windows with heavy glass (1/4") and a 3" separation are necessary to bring the STC rating of the windows to 45. Non-opening windows are best.

4. Seal Joints and Cracks (exposed side only)
The heavy sound-blocking walls and windows will be nearly useless if a direct air-path exists for the noise to go into the building. All cracks, joints, and construction openings must be sealed with a high-density sealant. Windows and doors must have excellent seals that are maintained and replaced regularly. (See the example in step 5 to gauge the impact of cracks and open joints in noise reduction.)

5. Minimize Exposed Wall, Window, and Door Area
One could follow steps 2 through 4 above on every exterior wall of a building to get good noise isolation. But one only needs to take the extra steps on surfaces directly exposed to the train tracks. Therefore, it makes sense to minimize the exterior wall area on the side exposed to the train tracks. Window area should be minimized because windows let in more noise than walls do. Minimizing the window area will help the overall sound loss through the outer wall. (EXAMPLE: a wall with an STC rating of 55 takes up half the area of a total surface and a window with STC rating of 45 takes up the other half. The combined STC rating for the surface is then only 48. Further, if 5% of the area was an open crack with STC 0, the overall STC rating would be only 10!) Doors are also a weak link and, whenever possible, should not be located on the exposed side.

6. Use First Building to Block Site
Placing one continuous building near the railway (no breaks in the façade) will create a shield for the rest of the site. It also means that only one surface of one building must be treated with steps 1 through 5.

7. Situate Rooms According to Privacy
Acceptable noise levels in a home vary by room. Bedrooms require the most privacy (maximum of 35 dB(A) according to the USEPA). Living and dining areas require less privacy (40 dB(A) maximum). Kitchen, Bathroom, and common areas require the least indoor noise privacy (45 dB(A) maximum). Therefore, less sensitive rooms should be placed closest to the exposed wall and more sensitive rooms should be placed furthest away (to gain added noise reduction by internal walls).

8. Place No Vents or other Openings Through Exposed Wall
Cracks and joints must be sealed to stop noise, so it makes sense that no large openings or holes should be placed in the exposed wall. Even if the holes are connected to ducts, lots of noise will travel into the building through the opening. All effort should be made to place needed openings on a non-exposed wall. Care should also be taken to shield any roof vents from the noise path.

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Last modified on November 27, 2000 by china@juintow.com.
 
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