Interface - The Journal of Wheel/Rail Interaction

NOISE & VIBRATION

Reducing Noise and Vibration on NYCT
January 1, 2005

Any problem affecting the New York City Transit is by default a big problem. The process of transporting more than four million passengers per day in 6,000 vehicles on more than 700 miles of elevated, underground at-grade mainline tracks, on a system that operates 24 hours a day, seven days a week, presents plenty of opportunity for problems to occur. One area that the NYCT and its riders have had to contend with is noise and vibration, particularly on elevated and underground lines. Vibration tends to create problems for the tenants of buildings near underground lines, while screech and wheel squeal are hard on residents' and passengers' ears.

Over the past several years, NYCT has implemented a number of track and vehicle treatments to reduce noise and vibration levels on the system. These treatments have reduced the average noise level on elevated and subway lines from 98 dBA in the 1970s and '80s to an average 88 dBA since 1990, Antonio Cabrera, NYCT's Director of Track Engineering, told delegates at Interface Journal and Advanced Rail Management's Rail Transit '04 Wheel/Rail Interaction Seminar. (See "Examining wheel/rail interaction on rail transit systems")

On the vehicle side, quieter traction motors installed during scheduled maintenance programs reduced noise levels by 5 - 7 dBA. Ring-damped wheels, which were installed on new and overhauled cars, and the installation of composition brake shoes, which reduce screech during braking, reduced screech noise by as much as 15 - 20 dBA. A wheel truing program aimed at eliminating "flat" wheels has also reduced noise levels. "Trued wheels are 10 - 15 dBA quieter than flat wheels," Cabrera said. New initiatives include the acquisition of 1,100 new cars with quieter traction motors, air compressors and composition brake shoes. NYCT's motor shop is equipped with dynamometer to monitor vibration levels of remanufactured motors.

On the track side, NYCT has made modifications to several of its existing track types, which include:
• Ballasted track in a concrete invert (type I).
• Dual-block timber ties embedded in concrete (type IIM), which incorporates long ties every fourth tie to which the third rail is mounted. This design represents the standard for subway reconstruction. "If the track remains dry, it can last 100 years," Cabrera said.
• Open-deck, steel elevated structure (type III).
• Ballasted track on fill, at grade (type VI).
• Direct fixation to structural invert (type VIII), which incorporates rubber rail seats resting on concrete or epoxy.

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