4 ms·

believe it or not, BART is actually competent and does what they can with the cards they have been dealt. name another US transit agency implementing a takt

GauntletWizard 4y ago
BART discovered conical instead of cylindrical wheels in 2018[1]. This is dawn-of-railroad technology. You can accuse BART of many things, but competency is not one of them. [1] https://www.bart.gov/news/articles/2018/news20180606 https://www.bart.gov/news/articles/2018/news20180606 Edit: Clarified what the issue was.
- mlyle 4y ago
  > BART discovered cylindrical wheels in 2018 ?? This is a 2018 piece describing how they moved from cylindrical wheels to an advanced wheel profile. I don't think they're claiming the new, non-cylindrical profile is particularly advanced, either, but just carefully optimized to maintain a single point of contact even as the wheel wears.
- deleted 4y ago
  [deleted]
- adolph 4y ago
  That doesn’t seem to be a charitable reading and in any case it has to do with wheel taper, more like cone than cylinder. More specifically the nature of the solution was getting two parts of the org, track and train, to work together. While that may seem elementary stuff, anyone at a big org can attest to how often it is tremendously difficult to do sometimes. I write this not as an apologist for commuter rail, which I find excessively expensive and inflexible outside of very circumstances, but as an excuse to link to the lovely Feynman description of why train wheels are tapered: https://m.youtube.com/watch?v=y7h4OtFDnYE https://m.youtube.com/watch?v=y7h4OtFDnYE
  - gooseyman 4y ago
    I used to joke when the Subway wheels squealed “yeah that’s how the engineers designed that” Turns out, it was.
- jjulius 4y ago
  >BART discovered cylindrical wheels in 2018. ... uhh, your own link says otherwise, emphasis mine... >To answer the question, the original BART wheel profile, you can consider it like a cylindrical section of pipe. While the new profile is tapered, like a curved barrel, if you could imagine that the cylinder shape pipe rolling down a slight incline it really just wants to go straight. It doesn’t want to turn to the left, it doesn’t want to turn to the right, it just wants to go straight. That’s what our original BART wheel is like. Whenever it would come to a turn the wheel flange is what makes that wheel turn and go around the curve and that results in a lot of extra wear. The new wheel shape that we call the BT-3 Wheel Profile tends to want to self-center between the rails and it even steers in the turns so the result is much less wear and noticeably less noise.
- andbberger 4y ago
  like i said, they do what they can with the cards that they were dealt. the initial design of the system was flawed in many ways, one of them being the cylindrical wheel profile
- Animats 4y ago
  More technical article on BART wheel geometry.[1] The old wheels were cylindrical but the rails were tapered to provide self-centering. This works well for straight track and large radius-curves. The trouble with conical wheels is that too much self-centering can induce sideways oscillation at high speeds. BART was designed for 80MPH, a high speed for the time and still fast for a transit system. BART was also the first rail system to have active suspension. Rail geometry, wheel geometry, and suspension all interact. High speed rail wheel and track profiles are a complicated problem. The Shinkansen system in Japan did a lot of work on this, as did the TGV developers in France. It took a while to get wheels, rails, and suspension to all work together well enough for high speeds. Now this is reasonably well understood, but it wasn't when BART was designed. [1] https://www.wheel-rail-seminars.com/archives/2016/rt-papers/RT%2006%20WRI%202016%20BART%20Final.pdf https://www.wheel-rail-seminars.com/archives/2016/rt-papers/...
  - inferiorhuman 4y ago
    Now this is reasonably well understood, but it wasn't when BART was designed Claiming that BART was ground breaking and could've never predicted the consequences of their design choices is quite revisionist. They got called out for their dangerous train control almost immediately. 80 MPH is not and was not high speed. Amtrak trainsets were cable of over 100 MPH back in the mid-70s. BART just reinvented everything poorly (that's their MO). Anyways here's a technical piece about BART wheels: https://www.bart.gov/sites/default/files/docs/noisereport.pdf https://www.bart.gov/sites/default/files/docs/noisereport.pd... With trued wheels and smooth ground rail on ballast and ties, BART is one of the quietest vehicles. in operation at U.S. transit systems. Problem is BART is exceptionally hard on their track. Even with conical wheels you can feel the new trains bounce up and down on wildly out of round wheels. You can feel the rumbling on the decrepit track between Lake Merritt and 19th St. Normal railways often lubricate their tracks, but BART can't. Normal railways increase the track gauge slightly in curves (because most train cars don't use differentials), BART pretty much doesn't. This was my favorite bit: Of these two types of curving noise, wheel squeal is the more prevalent, while wheel howl may be limited to lightly damped aluminum centered wheels such as used at BART. In fact, wheel howl may be unique to BART, because BART is the only transit system employing rigid aluminum centered wheels. Whoops.

GauntletWizard 4y ago

BART discovered conical instead of cylindrical wheels in 2018[1]. This is dawn-of-railroad technology. You can accuse BART of many things, but competency is not one of them. [1] https://www.bart.gov/news/articles/2018/news20180606 https://www.bart.gov/news/articles/2018/news20180606 Edit: Clarified what the issue was.

mlyle 4y ago
> BART discovered cylindrical wheels in 2018 ?? This is a 2018 piece describing how they moved from cylindrical wheels to an advanced wheel profile. I don't think they're claiming the new, non-cylindrical profile is particularly advanced, either, but just carefully optimized to maintain a single point of contact even as the wheel wears.
deleted 4y ago
[deleted]
adolph 4y ago
That doesn’t seem to be a charitable reading and in any case it has to do with wheel taper, more like cone than cylinder. More specifically the nature of the solution was getting two parts of the org, track and train, to work together. While that may seem elementary stuff, anyone at a big org can attest to how often it is tremendously difficult to do sometimes. I write this not as an apologist for commuter rail, which I find excessively expensive and inflexible outside of very circumstances, but as an excuse to link to the lovely Feynman description of why train wheels are tapered: https://m.youtube.com/watch?v=y7h4OtFDnYE https://m.youtube.com/watch?v=y7h4OtFDnYE
- gooseyman 4y ago
  I used to joke when the Subway wheels squealed “yeah that’s how the engineers designed that” Turns out, it was.
jjulius 4y ago
>BART discovered cylindrical wheels in 2018. ... uhh, your own link says otherwise, emphasis mine... >To answer the question, the original BART wheel profile, you can consider it like a cylindrical section of pipe. While the new profile is tapered, like a curved barrel, if you could imagine that the cylinder shape pipe rolling down a slight incline it really just wants to go straight. It doesn’t want to turn to the left, it doesn’t want to turn to the right, it just wants to go straight. That’s what our original BART wheel is like. Whenever it would come to a turn the wheel flange is what makes that wheel turn and go around the curve and that results in a lot of extra wear. The new wheel shape that we call the BT-3 Wheel Profile tends to want to self-center between the rails and it even steers in the turns so the result is much less wear and noticeably less noise.
andbberger 4y ago
like i said, they do what they can with the cards that they were dealt. the initial design of the system was flawed in many ways, one of them being the cylindrical wheel profile
Animats 4y ago
More technical article on BART wheel geometry.[1] The old wheels were cylindrical but the rails were tapered to provide self-centering. This works well for straight track and large radius-curves. The trouble with conical wheels is that too much self-centering can induce sideways oscillation at high speeds. BART was designed for 80MPH, a high speed for the time and still fast for a transit system. BART was also the first rail system to have active suspension. Rail geometry, wheel geometry, and suspension all interact. High speed rail wheel and track profiles are a complicated problem. The Shinkansen system in Japan did a lot of work on this, as did the TGV developers in France. It took a while to get wheels, rails, and suspension to all work together well enough for high speeds. Now this is reasonably well understood, but it wasn't when BART was designed. [1] https://www.wheel-rail-seminars.com/archives/2016/rt-papers/RT%2006%20WRI%202016%20BART%20Final.pdf https://www.wheel-rail-seminars.com/archives/2016/rt-papers/...
- inferiorhuman 4y ago
  Now this is reasonably well understood, but it wasn't when BART was designed Claiming that BART was ground breaking and could've never predicted the consequences of their design choices is quite revisionist. They got called out for their dangerous train control almost immediately. 80 MPH is not and was not high speed. Amtrak trainsets were cable of over 100 MPH back in the mid-70s. BART just reinvented everything poorly (that's their MO). Anyways here's a technical piece about BART wheels: https://www.bart.gov/sites/default/files/docs/noisereport.pdf https://www.bart.gov/sites/default/files/docs/noisereport.pd... With trued wheels and smooth ground rail on ballast and ties, BART is one of the quietest vehicles. in operation at U.S. transit systems. Problem is BART is exceptionally hard on their track. Even with conical wheels you can feel the new trains bounce up and down on wildly out of round wheels. You can feel the rumbling on the decrepit track between Lake Merritt and 19th St. Normal railways often lubricate their tracks, but BART can't. Normal railways increase the track gauge slightly in curves (because most train cars don't use differentials), BART pretty much doesn't. This was my favorite bit: Of these two types of curving noise, wheel squeal is the more prevalent, while wheel howl may be limited to lightly damped aluminum centered wheels such as used at BART. In fact, wheel howl may be unique to BART, because BART is the only transit system employing rigid aluminum centered wheels. Whoops.