It's actually not so bad in NYC. Yea -- there are some turns that involve screeching...but try the El in Chicago...or worse yet the BART in San Francisco. The latter sounds like it's trying to blow your ears off.

-W

There are several reasons why the NYC subways are noisier. Part of it has to do with the type of construction with all of the steel columns that causes more sound bouncing that plain concrete. The main reason is the boggies on NYC subways until recently. They are heavy duty, old style, all steel construction because many in NYC Transit believed they were more durable than newer designs. The older cars also have less sound insulation. Newer bogie designs are quieter and provide a smoother ride. The cars, the ones with automated annoucements, have newer boggies as well as more sound insulation. The main design of all cars are NYC Transit regarless who constructed them. That's how you can have identical looking cars built by Bombardier, Alstom, or Kawasaki.

Bolding mine.

Took the words right out of my mouth. ^

OP, never go near the Green Line westbound track at Government Center in Boston. You'll go deaf. It screeches so loudly that if the T decided to sell earplugs at that stop alone, they'll make up their budget deficit in a week.

Another +1.

And it's not just the T, either. Everything the MBTA is involved in is loud, with the sole exception of the human announcements.

Many times I have napped on the L in Chicago - after riding it for years I don't even notice the noise unless I'm talking directly to someone.

I think it's part of the charm. That dun dun dun DUH noise the trains make as they're pulling out of the station is a sound as quintessential to New York as any I can think of. Oh and if you think it's loud, you should have taken it 15 years ago when they still ran the older R33 "Redbirds" and more of the R32 style subway cars. Now THOSE were loud! :D

Wow, I remember those trains from growing up and trips to NYC on the weekends. Usually covered in graffiti.

On the issue of track curves, etc -- I remember there was a station once where the curve was so tight compared to what the train could do, that there were metal platform extenders that had to mechanically extend out to meet the train doors. What was that?

There are some trains and some lines that are obnoxiously loud and screechy. I've lived in NYC for 6 years now, both in Manhattan and Brooklyn. The older tracks and the older trains (especially the F and the A older models) can be deafening when they hit certain corners. You see many people covering their ears.

I've lived in Moscow before, and while the stations are much cleaners and very opulent, I found the Moscow metro to be much louder. Generally speaking, you can have a conversation in an NY subway car. Not the case in Moscow, especially on the older trains. I do recall, prior to living in NYC (when I lived in a Southern US city with no public rail transit) visiting Paris and remarking on how quiet the trains were there. Nearly silent, I thought. It felt like they were running on rubberized wheels.

I think most New Yorkers are used to the noise and a good majority actually supplement/ignore the train noise (along with the homeless and the "performers") by adding their own soundtrack through iPods/iPhones/etc. Actually, the most annoying noise in the train is made by people who have crappy headphones that leak sound and they blast their music on full tilt. I'd rather the train be louder.:mad:

The Union Square stop on the 4/5/6 currently has them for the downtown trains, and the South Ferry stop on the 1 also did until a recent renovation.

I don't think you can do too much about steel on steel. Have a relatively-new (in it's 28th year or so now) light rail system in my town and any curve it goes around can be loud. I don't think the NYC subway is appreciably louder than some of the London Underground lines FWIW.

To answer the OP's question, the answer is composed of the following parts:
track quality and maintenance, wheel quality, train design and the surrounding environment.

The noise comes from wheels going over rail joints and wheels going over tight curves.

Track quality -- Most of the older track is not welded, but screwed together at joints. The joints create the most amount of noise when weels go over them.

Older track is ballasted (track sits on a bed of small rocks or ballast). This has the advantage of cushioning the track and allowing for damping of vibrations if the track is maintained well. You also need to completely change the ballast out every 30-40 years. The quietest metro I've ever been on is in Munich and it has ballasted track. Ballasted track requires more maintenance to keep the rails properly aligned.

Newer track usually sits on concrete slabs, or concrete that's a part of the tunnel. Ideally you have some sort of a vibration isolator (a rubber pad of sorts) between the rails and the concrete.

Both for older and newer track, a rail grinder needs to periodically go over the track and grind it down a few millimeters at a time to maintain a proper track profile to minimize the amount of contact between the wheel and the rail. If you see a shiny rail top, chances are -- this profile is out of alignment.

wheel quality -- a wheel has to have a certain profile for minimizing noise. The wheel ideally would be ground down to a specific shape to minimize the contact area with the rail. This shape will get deformed when the train starts and stops hard and causes the wheels to spin or lock up, when it goes over tight curves, and when it operates on poorly-maintained track.

You can sometimes tell that the wheel has not been machined in a while and the train has a flat wheel -- the sound is like a wheel going over a joint, but at twice the rate. A flat wheel also messes up the rails.

Train design -- this is probably secondary to what I said above, but brake design is important here, otherwise you'll have screeching brakes all the time. Older DC motors also made very low-pitched noises, which increased the overall noise level (ride the Lo-V or another heritage NYC subway train to see what I'm talking about)

Surrounding environment -- tiles in the stations don't help with the noise as they are quite good at reverberating it. Tunnels that have 4 tracks with column support vs. 1 track in a tube actually improve noise dissipation. In a single-track tube you have noise reverberating from all sides.

In Moscow (and other ex-soviet metros), the problem with the older trains is that there's no forced ventilation. When the train is moving, big paddles allow air to come in. This was an ingenious design of the 1930s (probably modified from the Berlin U-Bahn cars, as those were the prototypes for the ex-Soviet A stock), and it worked quite well at the time. Now you really need forced ventilation (just fans doing their thing).

The system is closed (it was designed to work independently during a nuclear attack), so the temperature in the tunnel is the same as in the stations, and it works quite well.

You have fans in shafts between stations sucking in or blowing out air from the street, and depending on whether it's summer or winter, you'll have more or less air being sucked in. The trains will push this air towards stations to warm/cool it.

Basically this eliminates the need for air conditioning the trains, as the whole system is at a constant temperature. Now they're doing something completely senseless -- installing aircon on new trains instead of modernizing shaft ventilators... the hot air has to go somewhere, so expect the average temp of the lines that have trains with aircon to go up.

To compare this with NYC, NYC subway has no set station spacing over the entire system, much of the system is above ground, requiring aircon, and the aircon makes the tunnels very hot, which is difficult to control as there enough vent holes to make controlling temperature in tunnels impossible. What IS possible, but difficult for other reasons is installing platform screen doors, and controlling the temperature inside stations, although this is quite expensive (both installation of PSDs and running the aircon), not to mention it's impossible at this point as there are still many door spacing configs among older trains.

Skytrain has linear motors, which make most of the noise.

Rubber tyred metros provide a really crappy ride quality. They can't reliably do anything over 30 mph. The noise that you hear on all the VAL systems and these rubber-tyred metros is due to motors not designed to operate above 35 mph, and the noise of tires on the track. VAL systems are great in that they don't require as much track maintenance as wheel-on-rail systems, but generally require a larger loading gauge for similar capacity and have their own problems.

It won't make an adverse dent in paradise. Steel wheel on steel rail is the best way to go noise-wise if you do the maintenance.

Go ride any modern rail system -- no noise. High speed trains that operate at 350 km/h make less noise than the NYC subway.

Ride any new urban, suburban or regional train in Germany and you'll see what I mean. ZERO noise. ZERO. People whisper when they talk to each-other, otherwise it'll seem like they're screaming. The trains also make very little noise if you're standing outside.

A freeway or even a major arterial produces much more noise from cars than any modern properly-designed rail system with proper curves. Go stand in any new rail station in the middle of a freeway (LA is closest to HNL that I can think of) and then compare the noise the train makes to the ambient noise.