Noisiest Track Segment
I am amazed at how some segments of track can be practically whisper quiet and others be deafening beyond belief. I know BART grinds the track to take out imperfections, reducing vibrations and the resulting noise they cause. However, I think there are certain track segments that are just inherently noisy no matter how much grinding is done. Let's take the track segment between Ashby and Downtown Berkeley in the Richmond direction, for example. Its basically straight, downhill in a tunnel and so loud that it can't be safe. I'm sure BART has gone over it with the grinder at some point. When traveling at high speed downhill, one can imagine that the trains momentum might cause the wheels to slip, creating the high-pitched screeching that makes ears bleed. Am I way off base here? Is there a better reason why this segment is so loud? What is the loudest segment you encounter on your commute and what are its characteristics?
I ride the Balboa Park to
I ride the Balboa Park to Downtown Berkeley segment and that segment fails in comparison to the 24th St Mission-Glen Park segment. It is pretty much impossible to talk to a seat-mate without yelling. I believe it incorporates a turn, so that might account for the deafening noise.
In some cases, I think it is
In some cases, I think it is the wheels on the cars that cause the noise because some cars I ride in are relatively quiet through the tube, orinda tunnel, 12th street tunnel, and the squeaky segment before walnut creek. The tube is awful.
Wheels (IMO) are fine, it's
Wheels (IMO) are fine, it's the rails. What used to be preventative maintenance now has evolved to repairing or replacing just before it becomes a danger. There are sections of rail north of MacArthur to Ashby that can be heard up in Tilden Park. The other track which is aerial is the Fremont line near High Street (south of Fruitvale) - the curve alignment is off a bit and the noise is deafening. Speed reduction in the trans-bay-tube SF bound has helped reduce the track noise.
From what I've heard they've
From what I've heard they've reduced trains only to PL2 in the tube, unless the train is really late and has been cleared by Central to go faster. I think that's helped somewhat, but another factor is the acoustical insulation of the cars.
Does anyone know if the C2 cars being overhauled are getting new insulation? I think the new composite material flooring might help the noise somewhat...
what about acoustical
what about acoustical insulation in tunnels and tubes?
the concrete or steel walls must make the place a echo chamber.
Could BRAT trains be fitted
Could BRAT trains be fitted with the hard "rubber like" wheels that roller coasters have? They seem to be quiet. Does anyone know if this has been proposed?
I can't stand it from civic center to daly city. I see a lot of people with ear plugs. It must be getting louder.
I don't think that would work
I don't think that would work as the traction current has to return through the running rails. Obviously, using any type of insulator for wheel material would prevent this.
There is a railcar wheel
There is a railcar wheel called a resilient wheel that has rubber blocks between the center and outside "tire" to reduce noise. It has steel in the middle of each rubber block to carry the return current. There is also a small braided shunt that is connected between the inner and outer sections that is visible on the outside. This is actually a "telltale" indicator that will be visibly blown open like a fuse if the wheel has failed to conduct current properly requiring removal of the car from service for repair.
Resilient wheels are used mostly on light rail vehicles. The old PCC cars still used on the Muni E line used them almost exclusively.
BART tested some resilient wheels a few years back and also experimented with lubricant sticks rubbing against the flange/tread interface to reduce wheel noise. This was done during a period when a significant investigation was made of noise sources and possible methods of mitigation. Neither method was implemented for lack of significant cost effective improvement.
Three noise problems with wheels that are dealt with in maintenance are flats, shelling and out of round condition.
Flats come from the wheel locking up and sliding along the rail, usually from some braking malfunction or very slippery rail. Flat spots are removed from the wheels on a wheel truing machine. The wheels are actually milled smooth.
Shelling comes from the work hardened metal that is sometimes left beneath a trued flat spot which then starts to flake off in service. Another pass through the wheel truing machine fixes it.
Out of round is just that, the wheel becomes oval by a few thousandths of an inch. This produces a rumbling and vibration. Again, the fix is a trip through the wheel truing machine.
Railcar wheels are just another one of those things that seem so simple if you don't know anything about them.
That is really cool.
That is really cool.
If a wheel is "trued" will it
If a wheel is "trued" will it not be smaller then it's sibling wheels and thus cause problems?
I would assume that all
I would assume that all wheels in a truck would be trued at the same time to the same dimensions.
The wheel truing machine cuts
The wheel truing machine cuts both wheels of the same axle simultaneously to the same size.
As far as the size of the wheels on the other axles of the same truck, there is a tolerance of 5/16 inch in diameter if memory serves (I've been gone for a little over two years, worked there for almost 24 years). This is for all cars to balance traction motor load.
For C cars you have to be within 1/2 inch of the truck on the other end of the car to keep motor currents from becoming too imbalanced (DC propulsion).
For the A/B cars, there is no tolerance requirement from one truck to the other since the AC propulsion uses an inverter for each truck. This is a definite plus.
For really bad flats, a C car can end up with all the wheels on the car being trued for tolerance reasons.
Sometimes, depending on the cause, all wheels will have flats regardless of car type.
Another consideration when truing wheels is the flange thickness. If the flange becomes thin, it is made thicker by cutting away wheel diameter to effectively create more flange.
The wheels start out new with a 30 inch diameter and are considerd fully worn and removed from service at just above 28 inches.
You think this gets complicated? There's plenty more "It's simple if you don't know anything about it" when it comes to BART tech.
I don't know how many times over the years I heard "Well, that's just stupid to do it like that" from people who had no clue of the details on technical subjects.
Knowing what I do, I have a lot of respect for the people who maintain the trains and the fact that BART works as well as it does.
Oh! I forgot about that
Oh! I forgot about that whole electricity thing.....Thanks for clearing that up.