4 ms·

But not on BART!

kentonv 5y ago
As of 2018, more than half the train cars had been updated to conical wheels: https://www.bart.gov/news/articles/2018/news20180606 https://www.bart.gov/news/articles/2018/news20180606 But yes, historically the awful screeching around corners was because BART used cylindrical wheels. It's also, apparently, why they can't run all night -- the tracks need nightly maintenance due to the grinding.
- Lammy 5y ago
  Some more info and photos can be found here (PDF warning): https://www.apta.com/wp-content/uploads/Resources/mc/rail/previous/2017rail/presentations/Presentations/Holland,%20Ben.pdf https://www.apta.com/wp-content/uploads/Resources/mc/rail/pr... https://www.bart.gov/sites/default/files/docs/New%20wheel%20profile%20Nov%202018%20R4.pdf https://www.bart.gov/sites/default/files/docs/New%20wheel%20...
- henearkr 5y ago
  I know other horribly screeching trains, e.g. the Paris metro. May it be for the same reason? If so, then the fix seems straightforward.
  - Jyaif 5y ago
    The Paris metro's noise does not compare with the incredible screeching of the BART. Also, I think the Paris metro has special requirements, including quite sharp turns which I'm not sure trains can handle. Some of the lines in Paris actually use tires with side rails to channel the train to handle this.
    - frosted-flakes 5y ago
      The Montreal metro also uses rubber-tired trains.
  - _jal 5y ago
    Some MTA lines (NYC) are awful, too. The J comes to mind.
- userbinator 5y ago
  I wonder what the reason for not making them conical in the first place was, given that this knowledge has been around for over a century now. Maybe they were worried about https://en.wikipedia.org/wiki/Hunting_oscillation https://en.wikipedia.org/wiki/Hunting_oscillation ?
- deleted 5y ago
  [deleted]
- matttproud 5y ago
  If you're curious about the constraints of BART and the history involved in its development that led to why it is the way it is, I can certainly recommend Michael Healy's book BART: The Dramatic History of the Bay Area Rapid Transit System. https://books.google.ch/books/about/BART.html?id=ubbwDwAAQBAJ&source=kp_book_description&redir_esc=y https://books.google.ch/books/about/BART.html?id=ubbwDwAAQBA....
  - kentonv 5y ago
    Heh... I don't think I have the patience to read a book about BART but I'd read the cliff notes on the cylindrical wheels decision. There are so many mentions of the cylindrical wheels on the internet but none of them explain why they were chosen when conical wheels were already well-understood at the time... I'm sure the engineers weren't just ignorant.
    - jcrawfordor 5y ago
      Cylindrical wheels were expected to reduce hunting oscillation and rail wear, which were particularly significant problems for BART because of the high speeds it operated at. The basic problem is that computer modeling was not yet available, and so the new design was validated experimentally using a set of instrumented test carriages on a short rail section built for the purpose. This found positive results on improved ride, but failed to detect the long-term problematic track wear. BART wheels have mostly been re-trued to a new profile which is not cylindrical, but also not quite a traditional conical section, and was designed with extensive use of computer modeling. The cylindrical wheel decision is closely related to the decision to use Indian/broad gauge, which was expected to provide a smoother ride as well as allowing more support equipment to be mounted under the car where it would produce less vibration. Both are decisions that have not stood the test of time, although the choice of Indian gauge cannot practically be reversed. But I think the discussion around this often pays the original designers far too little credit: BART was intentionally a highly innovative design with numerous aspects that were somewhat experimental. BART's automated control system, for example, was such a debacle that BART initially operated with signal towers and the control system required nearly complete replacement. But it was a completely trailblazing design, and the same missteps would have to be made somewhere. BART was used once again as a test platform for an innovative radio control scheme in the 2000s, evidence of which can still be seen mounted trackside on the SFO wye. Many lessons learned from BART's performance have contributed to later designs around the world, including notably the DC Metro which was built just shortly after by some of the same contractors.
m0llusk 5y ago
Shinkansen use cylindrical wheels, but the tracks and wheels are kept maintained to an unusually high standard.

But not on BART!

As of 2018, more than half the train cars had been updated to conical wheels: https://www.bart.gov/news/articles/2018/news20180606 https://www.bart.gov/news/articles/2018/news20180606 But yes, historically the awful screeching around corners was because BART used cylindrical wheels. It's also, apparently, why they can't run all night -- the tracks need nightly maintenance due to the grinding.

Lammy 5y ago
Some more info and photos can be found here (PDF warning): https://www.apta.com/wp-content/uploads/Resources/mc/rail/previous/2017rail/presentations/Presentations/Holland,%20Ben.pdf https://www.apta.com/wp-content/uploads/Resources/mc/rail/pr... https://www.bart.gov/sites/default/files/docs/New%20wheel%20profile%20Nov%202018%20R4.pdf https://www.bart.gov/sites/default/files/docs/New%20wheel%20...
henearkr 5y ago
I know other horribly screeching trains, e.g. the Paris metro. May it be for the same reason? If so, then the fix seems straightforward.
- Jyaif 5y ago
  The Paris metro's noise does not compare with the incredible screeching of the BART. Also, I think the Paris metro has special requirements, including quite sharp turns which I'm not sure trains can handle. Some of the lines in Paris actually use tires with side rails to channel the train to handle this.
  - frosted-flakes 5y ago
    The Montreal metro also uses rubber-tired trains.
- _jal 5y ago
  Some MTA lines (NYC) are awful, too. The J comes to mind.
userbinator 5y ago
I wonder what the reason for not making them conical in the first place was, given that this knowledge has been around for over a century now. Maybe they were worried about https://en.wikipedia.org/wiki/Hunting_oscillation https://en.wikipedia.org/wiki/Hunting_oscillation ?
deleted 5y ago
[deleted]
matttproud 5y ago
If you're curious about the constraints of BART and the history involved in its development that led to why it is the way it is, I can certainly recommend Michael Healy's book BART: The Dramatic History of the Bay Area Rapid Transit System. https://books.google.ch/books/about/BART.html?id=ubbwDwAAQBAJ&source=kp_book_description&redir_esc=y https://books.google.ch/books/about/BART.html?id=ubbwDwAAQBA....
- kentonv 5y ago
  Heh... I don't think I have the patience to read a book about BART but I'd read the cliff notes on the cylindrical wheels decision. There are so many mentions of the cylindrical wheels on the internet but none of them explain why they were chosen when conical wheels were already well-understood at the time... I'm sure the engineers weren't just ignorant.
  - jcrawfordor 5y ago
    Cylindrical wheels were expected to reduce hunting oscillation and rail wear, which were particularly significant problems for BART because of the high speeds it operated at. The basic problem is that computer modeling was not yet available, and so the new design was validated experimentally using a set of instrumented test carriages on a short rail section built for the purpose. This found positive results on improved ride, but failed to detect the long-term problematic track wear. BART wheels have mostly been re-trued to a new profile which is not cylindrical, but also not quite a traditional conical section, and was designed with extensive use of computer modeling. The cylindrical wheel decision is closely related to the decision to use Indian/broad gauge, which was expected to provide a smoother ride as well as allowing more support equipment to be mounted under the car where it would produce less vibration. Both are decisions that have not stood the test of time, although the choice of Indian gauge cannot practically be reversed. But I think the discussion around this often pays the original designers far too little credit: BART was intentionally a highly innovative design with numerous aspects that were somewhat experimental. BART's automated control system, for example, was such a debacle that BART initially operated with signal towers and the control system required nearly complete replacement. But it was a completely trailblazing design, and the same missteps would have to be made somewhere. BART was used once again as a test platform for an innovative radio control scheme in the 2000s, evidence of which can still be seen mounted trackside on the SFO wye. Many lessons learned from BART's performance have contributed to later designs around the world, including notably the DC Metro which was built just shortly after by some of the same contractors.

m0llusk 5y ago

Shinkansen use cylindrical wheels, but the tracks and wheels are kept maintained to an unusually high standard.