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| Re: MTA removes or increases more speed limits (1506856) | |||
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Re: MTA removes or increases more speed limits |
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Posted by Stephen Bauman on Wed Mar 13 10:10:13 2019, in response to Re: MTA removes or increases more speed limits, posted by randyo on Wed Mar 13 01:34:47 2019. It was due to complaints from the residents of the housing projects that were built on the east side of Bway in the area in the late 1950s.One of the world's experts on noise control was a Columbia University professor around that time. It's a shame the TA did not consult with him. He was always looking for real life situations for his teaching his lab courses. I took his courses in the late 1960's because acoustics was an interest I did not pursue while in college and graduate school. Some time in the late 1980s newly developed noise deadening tie plates were installed in the area. One key to noise reduction is determining how it's transmitted. It can be through air or through solids (e.g. train wheels to rails to ties to steel elevated structure). The "sound deadening tie plates" are mounted on a rubber layer. This rubber layer decouples some of the vibrations from crossing the rail-rail tie interface. Much better results are obtained when there are two decoupling barriers. This could be accomplished, if the ties also rested on rubber. A second strategy is to reflect any airborne noise at the track away from the apartment houses. This strategy is employed by the JFK AirTrain. The el structure has exterior walls that extend well above track level. They reflect any airborne noise upward and away from sides of the structure. |
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