Noise levels on Neponset bridge

[NimrodWildfire]

I live within the vicinity of the two sets of tracks on the two rail bridges going over the Neponset River. I'm not even particularly close, but the level of noise pollution is really starting to get to me. Is there anything that can be done about this? I heard about something called continuous welded rail, which I'm sure you all know about, so I'm wondering if that might help some? Would slightly slower speed make much of a difference? Right now it seems to take the T trains about 30 seconds to cover the bulk of it—during that time, my amateur measurement app recorded a dBa level of 108, with the average over those 30ish seconds around 101 dBa. This seems loud to me, but I'd love your input.
Thanks.

[Gerry6309]

There are two types of sound which emanate from a moving train, high pitched clicks and squeals and low pitched rumbles. The high pitched stuff is controlled by the use of a closed deck as on the Neponset bridges. The rumbling sounds, at low frequencies penetrate further and propagate farther than the high pitched sounds. A thick layer of ballast between the rails and the deck will absorb some of this.

The rapid transit bridge uses steel stringers under a concrete deck, to which the rails are attached with rubber pads. There is no sound absorbing material like ties and ballast.

The commuter rail bridge uses a suspended deck, where the weight is carried on the heavy beams to either side of the tracks. Lighter cross stringers and a concrete deck occupy the space between. This was done to reduce the grade necessary to gain clearance over the river. I don't know whether ties and ballast or direct fixation is used under the rails, but because of this design, the view is severely limited from the rapid transit trains westerly. If the deck uses direct fixation, the rumbles will be AMPLIFIED by the sounding board effect, and concentrated by the side girders. Thankfully I live on the west side of Popes Hill!

[MBTA F40PH-2C 1050]

that section of the railroad for Commuter trains, which carries the Old Colony line, does have CWR, unfortunately for you, where the bridge spans start on each end, there are breaks in the rail. Think of the rail head as your two forearms. point your fingers straight out (Left to Right vertically in front of you), and drop your arms horizontally so that your fingers fall back to front, forming a continues section of your arms L to R across your chest. The way that your fingers line up (a slanted line) is what the Commuter Rail section of the bridge looks like, as is probably the Red Line section. To answer your question simply, there is nothing that can be done about this. As the previous poster wrote, the sound is amplified as trains go over the bridge

[MBTA3247]

There doesn't appear to be any ballast on the commuter rail bridge in the satellite photos (though there is for the Red Line), so there's nothing there to dampen the sound.

[boblothrope]

I live within the vicinity of the two sets of tracks on the two rail bridges going over the Neponset River. I'm not even particularly close, but the level of noise pollution is really starting to get to me. Is there anything that can be done about this? I heard about something called continuous welded rail, which I'm sure you all know about, so I'm wondering if that might help some? Would slightly slower speed make much of a difference?

In my experience, most train noise around here isn't caused by rail joints.

On the Red Line, it's caused by flat spots on the wheels.

On the Commuter Rail, it's caused by the engine. And sometimes there are screeching noises on curves. Is this a particular problem for the Rotems?

[MBTA F40PH-2C 1050]

There doesn't appear to be any ballast on the commuter rail bridge in the satellite photos (though there is for the Red Line), so there's nothing there to dampen the sound.

It is a ballast decked bridge. Trains are noisy pieces of machinery...everything makes noise on a train, the wheels, locomotives, rails, rail joints...they are just loud

[dbperry]

What about wheel flanges grinding against the rail? Like the green line going around the Park Street curve? Not likely on commuter rail lines unless the track is out of alignment, but is that a possible source of noise at this location?

[TomNelligan]

For the last couple decades I have lived (by choice) a couple hundred feet from one of the North Side commuter lines. My living room is on the railroad side and when the windows are open, the noise of passing trains is enough to momentarily drown out my TV. It's mostly the noise of the locomotive, plus the general swoosh of the wheels. The noise doesn't bother me, but if it did, I'd expect people to point out that the railroad was there for roughly 150 years before I was.

This is not to say that I'm unsympathetic to the original poster, who asks a very reasonable question. But if he's new to his neighborhood, I'd suggest that you get used to the sound after a while. People lived along the Washington Street el for a hundred years with trains a few feet from second floor windows and they somehow survived!

[Gerry6309]

People lived along the Washington Street el for a hundred years with trains a few feet from second floor windows and they somehow survived!

The El was an open decked structure with ties laid on he steel spans, a design still in widespread use in Chicago and New York. There is no sounding board, and the sound disperses in all directions. The clicks and squeals are not absorbed. Rail on els is frequently ground and wheels maintained to reduce noise.

When the Pink (Douglas) line was rebuilt in Chicago, new concrete columns were used, but the spans and tracks used traditional open deck methods.

[F-line to Dudley via Park]

It also depends on weather and air pressure. The Red Line over the Longfellow can be terrifyingly loud from a long distance away some mornings. As far up as BU Bridge. And then other days you can stand in the same exact spot and watch the trains go back and forth off it silently.

Fresh Pond Reservation, where I do a morning jog, is an interesting place for that phenomenon. It's right by the Fitchburg Line, but some days I can hear the constant hum of and Pike traffic and occasional rumble of the Worcester Line better from the path around the pond than I can hear the Fitchburg a few blocks away.

[Bramdeisroberts]

It also depends on weather and air pressure. The Red Line over the Longfellow can be terrifyingly loud from a long distance away some mornings. As far up as BU Bridge. And then other days you can stand in the same exact spot and watch the trains go back and forth off it silently.

Fresh Pond Reservation, where I do a morning jog, is an interesting place for that phenomenon. It's right by the Fitchburg Line, but some days I can hear the constant hum of and Pike traffic and occasional rumble of the Worcester Line better from the path around the pond than I can hear the Fitchburg a few blocks away.

Ditto for me in Waltham. I'm about 3/4 miles south of the Fitchburg line, and in the right conditions I can hear the late trains on the Worcester line over a mile away to the south.

As to the original topic, I spend a fair amount of time nearish to the Neponset bridge, and the big thing I've noticed is A: How frequently you see HSP46-hauled trainsets cross the bridge, and B: How much quieter the HSP's are than the rest of the T's locomotive fleet.

It seems that in terms of noise it's HSP46 << F40PH-2C <<<<<<<... ...<<<<<<< GP40MC. Those HEP units are damn near as loud as the screamers.

[F-line to Dudley via Park]

It also depends on weather and air pressure. The Red Line over the Longfellow can be terrifyingly loud from a long distance away some mornings. As far up as BU Bridge. And then other days you can stand in the same exact spot and watch the trains go back and forth off it silently.

Fresh Pond Reservation, where I do a morning jog, is an interesting place for that phenomenon. It's right by the Fitchburg Line, but some days I can hear the constant hum of and Pike traffic and occasional rumble of the Worcester Line better from the path around the pond than I can hear the Fitchburg a few blocks away.

Ditto for me in Waltham. I'm about 3/4 miles south of the Fitchburg line, and in the right conditions I can hear the late trains on the Worcester line over a mile away to the south.

As to the original topic, I spend a fair amount of time nearish to the Neponset bridge, and the big thing I've noticed is A: How frequently you see HSP46-hauled trainsets cross the bridge, and B: How much quieter the HSP's are than the rest of the T's locomotive fleet.

It seems that in terms of noise it's HSP46 << F40PH-2C <<<<<<<... ...<<<<<<< GP40MC. Those HEP units are damn near as loud as the screamers.

No HEP engine certainly makes a difference. AC loco's inverter replacing the separate HEP generator + faster/more-powerful acceleration = more time spent at cruising speed, where the lone engine spending quite a bit overall less time at higher notch means it makes quite a bit less noise over longer stretches. Even if decibel level is more or less indistinguishable from the older locos when starting out of a dead stop at a station.

[Bramdeisroberts]

No HEP engine certainly makes a difference. AC loco's inverter replacing the separate HEP generator + faster/more-powerful acceleration = more time spent at cruising speed, where the lone engine spending quite a bit overall less time at higher notch means it makes quite a bit less noise over longer stretches. Even if decibel level is more or less indistinguishable from the older locos when starting out of a dead stop at a station.

It also seems that the GE prime mover is significantly quieter than the 645 is, which makes sense because it's a 4-stroke 12cyl engine vs a 2-stroke 16cyl engine. For a given RPM range, that means that the GE mill has less than half the frequency of combustion events, which leads to a lower-pitched engine note that's less offensive on the ears. The bigger individual cylinders of the GE mill also help, as the bigger the cylinder, the lower-pitched the sound, which again makes the engine more pleasant on the ears.

[Gerry6309]

The major issue is 56 or more imperfect wheels rolling along imperfect rail, generate a distinct rumble, which is amplified by the sounding board effect.