4 ms·

There should be targeted interventions to address them imo. They are targeted. The issue is that in the end, it's a geometry problem -- in curves, one wheel wa

There should be targeted interventions to address them imo. They are targeted. The issue is that in the end, it's a geometry problem -- in curves, one wheel wants to move faster than the other, which results in one wheel flange being dragged across the railhead. The treatments range from the minor (friction modification such as lubricants or sand) to the major (independent wheels, steerable trucks, wheel/rail dampers) and all have affects on vehicle performance on tangent track, or high costs.

hedora 7y ago
The BART screeches with the worst of them (especially the trans bay tube — you basically can’t hold a conversation in it). I heard from someone that rode it when it was new that it used to be much, much quieter. So, I’m not sure I buy that the current level of screeching is by design, and not due to lack of maintenance.
- Anechoic 7y ago
  BART's issue is track corrugation, and they've been fighting that for many decades now.
- saltcured 7y ago
  A confounding factor is that I think they have changed the typical operating speeds in many parts of the BART system over the years. Also, it isn't like the entire system is made up of 40-50 year old, original parts. Train cars, wheels, sections of rail, and maybe even bits of rail-bed have been added to the system, renovated, and/or replaced over the years. Qualitatively, I think that I have experienced similar painful noises in every decade since the late 1970s, when I was a little kid and my father worked for BART. In the early 1990s, I can remember people talking about how they sometimes got a quiet train or a loud train on a familiar commute. We had similar observations about different road surfaces put down by Caltrans. I tend to ride it at least once every 2-3 years during return visits. Also, at various places in the East Bay, weather depending, you can hear the early morning trains on at-grade or above-grade track from quite far away. I have heard very similar noises in recent years when visiting the same places, giving me a nostalgic kick as it sounded so familiar.
Symbiote 7y ago
I think you can also cant the track, but I don't know if this is appropriate for a metro system.
Doxin 7y ago
The usual solution to this is gentle curves and conical wheel shapes. In a curve the train tilts slightly causing the wheels on the inside of the curve to run on a smaller diameter of the wheel and the wheels on the outside on a larger diameter. Of course once you have tight turns or cylindrical wheels (wtf BART) you get godawful screeching.
- Anechoic 7y ago
  The usual solution to this is gentle curves and conical wheel shapes Standard wheels are conical. You can optimize the wheel and track profiles for curves, but that may affect the wheel behavior on tangent track where "hunting" might occur.
  - Doxin 7y ago
    They are, which is why I called it the usual solution. A lot of trams and subways use too tight curves (which can't really be avoided all the time) but then there's the BART which uses cylindrical wheels for no good reason except it's expensive to change now. It's a tricky problem for sure, and I didn't intend to solve it with my comment, just shed some light on what the problem space actually is to people less familiar.

hedora 7y ago

The BART screeches with the worst of them (especially the trans bay tube — you basically can’t hold a conversation in it). I heard from someone that rode it when it was new that it used to be much, much quieter. So, I’m not sure I buy that the current level of screeching is by design, and not due to lack of maintenance.

Anechoic 7y ago
BART's issue is track corrugation, and they've been fighting that for many decades now.
saltcured 7y ago
A confounding factor is that I think they have changed the typical operating speeds in many parts of the BART system over the years. Also, it isn't like the entire system is made up of 40-50 year old, original parts. Train cars, wheels, sections of rail, and maybe even bits of rail-bed have been added to the system, renovated, and/or replaced over the years. Qualitatively, I think that I have experienced similar painful noises in every decade since the late 1970s, when I was a little kid and my father worked for BART. In the early 1990s, I can remember people talking about how they sometimes got a quiet train or a loud train on a familiar commute. We had similar observations about different road surfaces put down by Caltrans. I tend to ride it at least once every 2-3 years during return visits. Also, at various places in the East Bay, weather depending, you can hear the early morning trains on at-grade or above-grade track from quite far away. I have heard very similar noises in recent years when visiting the same places, giving me a nostalgic kick as it sounded so familiar.

Symbiote 7y ago

I think you can also cant the track, but I don't know if this is appropriate for a metro system.

Doxin 7y ago

The usual solution to this is gentle curves and conical wheel shapes. In a curve the train tilts slightly causing the wheels on the inside of the curve to run on a smaller diameter of the wheel and the wheels on the outside on a larger diameter. Of course once you have tight turns or cylindrical wheels (wtf BART) you get godawful screeching.

Anechoic 7y ago
The usual solution to this is gentle curves and conical wheel shapes Standard wheels are conical. You can optimize the wheel and track profiles for curves, but that may affect the wheel behavior on tangent track where "hunting" might occur.
- Doxin 7y ago
  They are, which is why I called it the usual solution. A lot of trams and subways use too tight curves (which can't really be avoided all the time) but then there's the BART which uses cylindrical wheels for no good reason except it's expensive to change now. It's a tricky problem for sure, and I didn't intend to solve it with my comment, just shed some light on what the problem space actually is to people less familiar.