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Metro consultants confirm resident fears regarding noise and vibrations

metro logoA consulting firm hired by Metro has confirmed local residents’ concerns about Metro’s new 7000 series trains – they are louder than the old ones and may have a tendency to vibrate more, shaking nearby homes.

Consultants from Wilson Ihrig, the firm Metro hired for the study, said in the report posted online March 24 that in all but one residential site tested, vibration from the trains was higher for the 7000 series, than the older ones. The study concluded this by measuring ground-borne vibration in houses a few hundred feet from the track centerline when a train passed by.

The report’s authors said some Metro trains violated the organization’s design criteria by go over the recommend vibrations for nearby homes.

The consultants said based on their months-long field study of various residences in and around the Green Line tunnels, Metro’s 7000 series trains are louder than the older series trains. The new trains cause more vibration in all but one residence tested within the study compared with the older series trains. While Wilson Ihrig tested both vibration and noise at the various testing sites, only the vibration levels exceeded Metro design criteria.

Metro spokesperson Sherri Ly said exceeding design criteria was not limited to the 7000 series.

Metro board member Tom Bulger, who lives in D.C. but outside the testing area, said he wasn’t concerned about the test results.

“We live in a city,” he said. “There’s noise.”

He said noise is part of living in an urban environment. If residents don’t want the noise, they can live in an ex-urban area with other sources of noise.

“Go far, far way and you can deal with animals – bears, deer and wolverines,” Bulger said.

He puts up with noise in his own neighborhood as well.

“Can I get garbage trucks on my street to not shake my house?” he said. “It’s called living in an urban environment,” he added.

Metro’s design criterion for noise is 40 decibels (dBA) for noise and 70 decibels (VdB) for vibration. Report authors said that for noise in terms of trains passing by a testing location, neither the 7000 series trains nor the other series trains averaged a noise levels at any testing locations at or greater than 40 dBA. Although 40 dBA is within WMATA design criteria, Federal Transit Administration officials would say noise levels of 40 dBA would annoy people living in homes nearby. For frequent noise events –more than 70 per day -- in a residential area, the noise must be 35 dBA or lower to not annoy residents.

Officials at the National Institute on Deafness and Other Communication Disorders, within the National Institutes of Health, said 45 dBA is the average sound decibel rating for the hum of a refrigerator; 60 dBA is the average sound rating for normal conversation and 85 dBA is the average decibel rating for heavy city traffic.

Transportation Engineer Gus Ubaldi, who helped design Metro’s tracks in the 1970s, said although some collected vibration and ground-borne noise data exceeded Metro design criteria, the study results showed there were no serious noise problems.

“They took ratings, their ratings were such that they weren’t up in excess of what is considered to be normal,” Ubaldi said. “I think 40 decibels is the noise level for being in a banquet hall with conversation going on.”

“The measurements say there really isn’t a problem here,” he added.

He said it was possible the increased noise and vibration had something to do with the train wheels, since report authors said Metro did not have rough tracks in the area of the vibration and noise study.

Metro employees had last completed grinding, or gotten rid of corrugation, on those sections of track in March 2017.

“Corrugation’s going to make it sound like going on over cobblestones, you know, but they’re saying there isn’t any [corrugation],” Ubaldi said.

@kathleenstubbs3

 

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