Interface - The Journal of Wheel/Rail Interaction

NOISE & VIBRATION

Reducing Noise and Vibration on NYCT (continued)

One of the first things NYCT did to reduce track-generated noise and vibration was to install cwr wherever possible. NYCT uses standard 115 RE rail section in open track, but is committed to a 110-pound ARA-B rail section in subway lines, most of which were built between 1904 and 1944, in order to maintain clearances. To date, NYCT has installed more than 320 miles of cwr—nearly half of the mainline track miles on the system. The use of cwr is not appropriate on old elevated structures, which require expansion joints every 200 feet, or in some tight radius curves on the system.

"Rails wear quickly in curves," Cabrera said. "With our high traffic levels and 24/7 operation it would be very difficult to change out cwr."

Overall, the use of cwr reduces noise by 5 to 7 dBA, compared to jointed rail on the system. The use of cwr also eliminates pounding at joints, which provides for a smoother ride and eliminates bolt hole cracks and broken rails. The use of resilient fasteners provides an additional 3-dBA reduction in noise.

A custom designed resilient, spring-loaded fastening system by Dynamic Engineering, which incorporates a resilient pad fixed between cast steel base and top plates that are fastened with springs under tension and clipped to the rail with a Pandrol Fastclip (see "Rail Fixation Reduces Vibration"), has further reduced noise by 3 dBA to 5 dBA on elevated lines. This system, which is also used on subway lines, does not trap moisture (which can be a source of rail base corrosion), as rubber rail seats used in the Type VIII direct fixation to structural invert do.

The use of resilient plates on its subway track, which typically consists of timber tie blocks embedded in concrete, has been shown to reduce the track modulus from the standard 10,000 - 20,000 psi range to 3,000 - 4,000 psi, which approximates the modulus of typical ballasted track.

NYCT is also experimenting with an 800-foot section of Low Vibration Track, which it is considering for all future construction. LVT, designed by the Permanent Way Corp., features reinforced concrete blocks with resilient pads that are encased in a rubber boot around which concrete is poured. "This provides a resilient track with components that are replaceable, which is very important when operating a 24-hour-per-day, seven-days-per-week system," Cabrera said.

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