There are actually several sources of noise caused by BART cars. These are radiated mostly to the sides by the parabolic shape of the aluminum wheel hubs. You couldn't ask for a better, more resilient sound radiator; or a more directional one, which of course concentrates sound magnificently. As follows:

1. Low frequency vibrations are generated by steel rolling on steel. And they are harmonically amplified wherever the trackway is more resilient, such as on an aerial; as anyone who lives near one surely knows. I hear them over two miles away, but only until they hit grade level, where they are suddenly much quieter. These harmonic vibrations also cause the rail surface to become corrugated (vertically wavy), which then significantly aggravates this noise.

BART Rail Grinder

2. Surface slide causes a higher pitched, sort of a squawky jetty sound. You hear it just as the video starts. it is very noticeable when echoed inside a tunnel - where it is sometimes earsplitting. Corrugated rail causes wheels to slide a bit, producing this sound. But it is also due to wheels not rolling square to the rails, and is common to all rail vehicles not equipped with radial trucks. Few are equipped, as this is a relatively new invention. Radial trucks ride with their wheel axis truly square to the rail around curves, as their axles are mechanically adjusted according to the angle of the truck. The longer the non-radial truck wheelbase, the worse it gets. It is especially bad where single wheel sets are rigidly mounted each end of a car.

3. Peculiar to third rail installations, and to some extent, overhead catenary, is a singing sound caused by electrical pick-ups lightly sliding along. This is not very loud, and usually is heard only if you are near the trackway as the train approaches or recedes away - but not as the train passes.

4. The awful squealing sound you can hear on almost all BART cars virtually everywhere is caused by wheel flanges rubbing on the "gauge corner" of the rails. You will also hear freight cars squeal sometimes, especially on curves when not at equalibrium speed (either higher or lower). Lately, the Capital Corridor cars have been squealing a lot more than they used to as well. It is indicative of tardy maintenance, but BART is running the wheels off those cars, as they are their own. The squealing sound gets louder and louder as the flanges wear. Because flanges loose their tracking ability unless the "Fillet Radius" is regularly maintained, wheels will scrape the rails more and more intensely; thus, more noise is produced.

In the case of BART, their literal re-invention of the wheel left it with a cylindrical tread, rather that the usual modern conical shape. As someone said a few posts back: since it wasn't broke, BART shouldn't have fixed it!. Though going against the existing standard gauge was stupid enough, that pales in comparison to this ultimate stupidity of all - cylindrical wheels.

With a conical shaped tread and a solid wheel set, the wheel set will "self track" around a curve, much like a cone rolling on the table. When at equilibrium speed and properly loaded, centrifugal force is just right to position the "cone" on the rails so that self tracking occurs. If that is not just right, the flange fillet radius comes into play next, non-linearly increasing or decreasing this conical effect. On well maintained wheels and rails, that is usually enough to properly track around a curve. But if more is still needed for any reason, the actual flange finally comes into play, but then scrapes the rail when doing so - making lots of really unpleasant noise. The conical wheel system really is the epitome of simplicity - elegance at its best.

BART has intensely suffered because of this folly, as their flanges are constantly in play even on straight track, making a lot of noise while severely wearing both wheel and rail. Though very light cars are used on a very heavily built trackway, rails on curves are barely lasting five years. Wheels don't last very long either. Cars with worn flanges bang from side to side violently sometimes, especially if on the rear car.

From what I hear from my connections at BART, I am sure BART entirely regrets their past fiddling with the wheels. Given that wheel sets not solidly connected by solid axles not only exhibit similar characteristics as BART's cylindrical wheels, but do so much more severely, Such wheels would most probably be regretted as well.

BTW, BART's folly was not in trying new ideas - not at all; but in failing to heed lessons already learned by the past mistakes of others. We either learn from the mistakes of the past, or we are doomed to repeat them. If we learn, then mankind can progress. Even if we make new previously unheard of mistakes - we still progress.

I hope that is helpful, to understand why railroad design engineers may seem stubborn at times. As a very old profession, we have already learned the hard way on a lot of things. On others, we continue to experiment.

OPB


P.S. - I forgot probably the biggest noisemaker of all: That being the clickityclack over jointed rail. Welded rail is much quieter, until it is worn down enough to expose hardened bumps at the welds. It then gets noisy too.