Trains Mag reported that the director said that BART was built for a diffrent era and has out lived its usefullness? Does she know something that we dont? Should I hold my breath when going under the bay in the tunnel?
IIRC she was talking about it outliving its usefulness in its present form, and needed longer trains, platforms, etc.
I'm more interested to learn why BART trains use flat aluminum wheels instead of traditional tapered steel wheels.
And I think the "lightweight" feature of BART trains might be a little bit over exagerrated. Their trains resemble contemporaries MARTA and WMATA a little more than BART would like to admit. Indian gauge and a higher DC voltage aren't such a big difference.
aegrotatioI'm more interested to learn why BART trains use flat aluminum wheels instead of traditional tapered steel wheels.
You might want to read up on composite wheels in general, and the design choice of track and wheel system used on BART in particular, before asking that question in that way.
A number of the design assumptions made for BART turn out, with hindsignt, to be ill advised. One of these was the flat (railhead) and comparatively rigid track; another was the use of the composite wheel (aluminum center with steel tire) -- the interaction between these leading to increased corrugation and poorer behavior on curves. I have never been quite sure that the engineers designing the BART track had understood Wickens et al. on actual rail-wheel dynamics or appreciated what the sources of noise were going to be (or the relative impact of those frequencies and amplitude of noise...)
As Dave Klepper has pointed out, when a system generates any significant level of corrugation, regular grinding or dressing becomes important. That doesn't happen on BART, for whatever combination of reasons. The last order of cars supposedly had increased coning of the steel treads, but that doesn't address the railhead profile or the attenuation of forces in the track.
Schlimm and some others here can comment on the use of true resilient wheels in European practice, where they are of great value but have contributed to at least one fairly high-profile accident. I can remember as a child reading about problems with transit cars that used a bonded rubber layer between sections of composite wheel (and finding what I thought was a solution: forming a 'screw' profile between the wheel sections and injecting the elastomer into that space to prevent the wheel from failing laterally even if the rubber deteriorated).
BART appears to be paying the price over and over for the "optimization of weight"and some of the resulting saving of cost in initial construction. Now they are 'stuck' with an infrastructure that apparently can't adopt stainless car construction or practical modern systems of track fixation. Note some of the reasons why relatively 'flat' wheel profile works on LGV/TGV, and how conditions differ from what is observed on BART.
The 'lightweight' aspect is, I think, a bit more profound than you indicate; this is '60s-style lightening, a bit like the philosophy behind the Cripes Turbotrain or some of the British APT, where aircraft-style methods were supposed to produce greater economies and modern electronics better operation. Even by the '70s it was apparent that much of the design philosophy (one example that has stuck with me was the design of the control system, which did not use a method like Gray code to protect against arbitrary speed change or determination) was not well-suited to railroad practice, even a railroad with dedicated track and no interchange requirements.
I have no particular quarrel with the unusual gauge, and I would agree that most of the professed arguments against it are a bit specious. If the early history of TGV development had not involved 'last-mile' use of existing standard-gauge lines, I think it is quite possible that a wider gauge would have been adopted for at least some LGV and more current HSR. Likewise I see nothing 'wrong' with going from 600/750V straight to 1000V and retaining third-rail power in this application -- although I'd have done the detail design of many of the elements there quite differently, again with hindsight the engineers in the '60s didn't have or insight they did not anticipate. As has been noted elsewhere, the spacing and number of substations that 1000V made nominally possible represented a reasonable cost optimization at the time, and to the extent that new transit projects at BART scale might be 'in the offing' it was also reasonable to assume that new construction might also benefit from 1000V experience and implementation.
Here is more on this - http://www.govtech.com/fs/Once-a-Ground-Breaking-Transit-Option-BART-Is-Not-What-is-Used-to-Be.html
Here is an example of technology gone amok. Would suggest title might be " is BART Technology out of date ". Maybe in ten years the title of a threa will be " Is PTC technology out of date ? " Making any technology possible to be future backwards compatible useable seems to be beyond the ability of many designers to grasp.
Any system needs to be built with interfaces that are independent and can be controlled by newer system sub parts. It is not easy.
aegrotatio And I think the "lightweight" feature of BART trains might be a little bit over exagerrated. Their trains resemble contemporaries MARTA and WMATA a little more than BART would like to admit. Indian gauge and a higher DC voltage aren't such a big difference.
Might be more accurate to say that the MARTA and WMATA trains resemble BART trains - BART opened several years before the other two.
A good number of the original Rohr built cars are still in service, so the weight reduction wasn't done to the point of adversely affecting fatigue life. The lihtweight does have advantages in reducing power consumption.
- Erik
erikem A good number of the original Rohr built cars are still in service, so the weight reduction wasn't done to the point of adversely affecting fatigue life. The lihtweight does have advantages in reducing power consumption. - Erik
blue streak 1 Question do the original car have regenerative braking that would help power consumption ?
I recall regenerative braking being a feature of the original BART system. Later improvements extend the range of braking effectiveness down to much lower speeds (similar to the technology for extended locomotive dynamic braking in some cases).
The big 'scam' in regenerative braking systems is that the energy produced by one train braking has to be used 'right then' or it is lost to heat before it does any good. The likelihood that one train on the system will 'happen to' be accelerating at just the right rate to utilize the regenerated power from a train in the same power section that is decelerating is relatively slight (although it always seemed to me that some form of communication-based train control could coordinate the two to some extent). A fix for this, which BART has been discussing, is some form of wayside power storage (where batteries, flywheel storage, etc. "soak up" the power produced by regenerative dynamic braking and then use that power to reduce voltage sag from starting trains as needed) - there are companies that now specialize in producing these installations.
I don't know if there are limitations on mixing newer and older equipment in the trains -- heaven knows there's enough mixing of consists in general; that's why I can never tell where the 'bicycle' cars will be in a given train. Someone here will know.
The original BART cars did indeed have regenerative/dynamic braking. The propulsion system included several resistors that would be connected across the 1000VDC bus when the voltage rose above 1100V (IIRC) in the case there was no other train in the electrical block to absorb the regenerated power. Problems with the resistor controls in the early years 1972-77 led to unexpectedly high wear with the friction brakes.
I don't remember what the lower limit was for regenerative braking, though the chopper circuits acted as a boost conveter during regeneration. The information in this post was based on a presentation by a couple of BART engineers at a weekly Electric Power Systems seminar at UCB ca 1976 (got my BSEE from Cal in 1976).
My memory of braking on Bart was back in the 70's or 80's and while not exactly braking, was the automatic speed control where the train would reach operating speed, overshoot, and brake, then accelerate and repeat. Speed up to 71, slow to 69, acelerate to 71. To much gain in the control loop and it needed some damping. It seemed that they could not find a balancing speed and it was disconcerting. I thought they changed some controls later that corrected it. Any info?
I found some old films that discuss BART's "blue sky" approach to transit engineering.
One of the more interesting points these films stress is how quiet the trains are designed to be both inside and out. However, BART riders and regulators have stated that they are some of the loudest rapid transit vehicles in the world, and in recent years they've even tried replacing and resurfacing miles of track to try to make the system less noisy with mixed results. The Transbay Tube is particularly deafening.
https://www.youtube.com/watch?v=vV-nsIUTKtE
https://www.youtube.com/watch?v=gzoZ3I-YPPs
https://www.youtube.com/watch?v=9NxWHafeVLA
BART saved one minute of travel time and uses half the trains that Key did.
https://www.youtube.com/watch?v=ObOLGzSnNHI
BART is also in the process of completely rebuilding the track structure to a more conventional style, hence why the new cars also have conventional wheels on them. Though they have to decide on how and when to do the conversion, without shutting down the system entirely, though it will require longer down time than is in the current schedule...it's certainly not a 24 hour operation(and I wouldn't want to be on a BART train in some of those areas during the night anyways).
Ahh, interesting. This topic came up in another thread, too.
http://cs.trains.com/trn/f/742/p/258385/2898932.aspx#2898932
Can we say that any segment of a rail system that is ~ 10 years or more old is probably out of date ? As well using 10+ year old tech for expansions ?. The problem is going all in on various technologies that slowly begin to not be nice to each other. We do not see facilities being built that can have fall back options so operations can proceed at a slower rate. That is this poster's concern for PTC as an example.
GERALD L MCFARLANE JR BART is also in the process of completely rebuilding the track structure to a more conventional style, hence why the new cars also have conventional wheels on them. Though they have to decide on how and when to do the conversion, without shutting down the system entirely, though it will require longer down time than is in the current schedule...it's certainly not a 24 hour operation(and I wouldn't want to be on a BART train in some of those areas during the night anyways).
BART wasn't designed to run 24/7. Not enough sidings or redundant track to allow maintenance. The last trains of the night leave the end-of-line stations around midnight and the first ones don't leave until 4am (later on weekends).
There are buses that cover a large portion of the system when the trains don't run. But they don't run very often, so there's a long wait if you miss the last BART train. (I speak from experience.)
Strength in diversity!
Interesting article from BART stating that water intrusion is causing major problems and repair will be major use of bond money.
https://www.bart.gov/news/articles/2016/news20160919-0
[quote user="droughtquake"]
blue streak 1 Interesting article from BART stating that water intrusion is causing major problems and repair will be major use of bond money. https://www.bart.gov/news/articles/2016/news20160919-0 http://www.bart.gov/news/articles/2016/news20160919-0
http://www.bart.gov/news/articles/2016/news20160919-0
The rainforest is getting a lot of press in BART. Leaking tunnels Wonder how that compares to NYC ?
daveklepperBART should start a program of installting high-speed crossovers, a pair between every station, and bi-dirctional train control and signalling. This would permit 24-hour operation and be very useful in emergencies
We here in Washington DC have crossovers, but they are definitely not high-speed crossovers. The stupid media here tend to call them "interlockings" even though they are nothing of the sort. They are very rarely used except at terminus stations where trains are turned around and at pocket tracks where skip-stop trains are parked, and at the rare spot where a colored line (like the Silver Line) turns around in the middle of a physical line (like the G Route, where Silver Line trains are supposed to reverse back to Whiele near Largo Town Center or where they were originally supposed to turn at Stadium-Armory but that crossover wasn't robust enough to maintain service).
Recently a major derailment happened over one of these crossovers that was being used regularly for single-tracking on the SafeTrack panic rebuilding program but our agency did not know that it had badly rotted ties since our track inspection and geometry cars until now did not routinely inspect crossovers (which media idiots still call "interlockings").
You also might know that WMATA is under extreme scrutiny as a result of their hastily implemented "SafeTrack" rebuilding program after some very high-profile accidents and an unprecedented sudden 28-hour shutdown to perform inspection of third-rail power equipment.
aegrotatio daveklepper We here in Washington DC have crossovers, but they are definitely not high-speed crossovers. The stupid media here tend to call them "interlockings" even though they are nothing of the sort. They are very rarely used except at terminus stations where trains are turned around and at pocket tracks where skip-stop trains are parked, and at the rare spot where a colored line (like the Silver Line) turns around in the middle of a physical line (like the G Route, where Silver Line trains are supposed to reverse back to Whiele near Largo Town Center or where they were originally supposed to turn at Stadium-Armory but that crossover wasn't robust enough to maintain service). Recently a major derailment happened over one of these crossovers that was being used regularly for single-tracking on the SafeTrack panic rebuilding program but our agency did not know that it had badly rotted ties since our track inspection and geometry cars until now did not routinely inspect crossovers (which media idiots still call "interlockings"). You also might know that WMATA is under extreme scrutiny as a result of their hastily implemented "SafeTrack" rebuilding program after some very high-profile accidents and an unprecedented sudden 28-hour shutdown to perform inspection of third-rail power equipment.
daveklepper
Call them crossovers, call them Control Points, call them Interlockings. Within the scope of WMATA's operating system they are all the same as they are controlled by the interlocked signal system to route trains through the location without interfereing (impacting) other trains. Absolute signals control train's entry to the crossovers on each track in both directions and if trains are to proceed from one track to another only one such train can proceed through at a time. If trains make straight track movements on each track then trains can move on each track at the same time in whatever direction the signals are cleared for.
Never too old to have a happy childhood!
BaltACD aegrotatio daveklepper We here in Washington DC have crossovers, but they are definitely not high-speed crossovers. The stupid media here tend to call them "interlockings" even though they are nothing of the sort. They are very rarely used except at terminus stations where trains are turned around and at pocket tracks where skip-stop trains are parked, and at the rare spot where a colored line (like the Silver Line) turns around in the middle of a physical line (like the G Route, where Silver Line trains are supposed to reverse back to Whiele near Largo Town Center or where they were originally supposed to turn at Stadium-Armory but that crossover wasn't robust enough to maintain service). Recently a major derailment happened over one of these crossovers that was being used regularly for single-tracking on the SafeTrack panic rebuilding program but our agency did not know that it had badly rotted ties since our track inspection and geometry cars until now did not routinely inspect crossovers (which media idiots still call "interlockings"). You also might know that WMATA is under extreme scrutiny as a result of their hastily implemented "SafeTrack" rebuilding program after some very high-profile accidents and an unprecedented sudden 28-hour shutdown to perform inspection of third-rail power equipment. Call them crossovers, call them Control Points, call them Interlockings. Within the scope of WMATA's operating system they are all the same as they are controlled by the interlocked signal system to route trains through the location without interfereing (impacting) other trains. Absolute signals control train's entry to the crossovers on each track in both directions and if trains are to proceed from one track to another only one such train can proceed through at a time. If trains make straight track movements on each track then trains can move on each track at the same time in whatever direction the signals are cleared for.
As long as it is impossible to establish a clear signal when the turnouts are lined against that move it meets the signal community's definition of an interlocking. When you say "it's nothing of the sort" I'd love to know what you think the "sort" is. You need to spend some time with your signal brothers!
One of the biggest problems BART has had, when the system was built and designed engineers tried to reinvent the wheel.
BART uses a dynamic brake system that when the track voltage is low feeds the third rail instead of brake grids on the car.(this is the description I was given back in the 70's).
Some of the problems they ran into(or ran into them), a 9volt signal system that "lost" trains and equipment. This was especially bad for the first train in the morning as overnight a layer would build of condensation would build up in the Bay Area fog. No steps for train operators to get out of the cars in yards. A real shortage of crossovers everywhere in the system. By 1978, six years after the system opened, a complete redesign of onboard train control equipment.(after a train ran off the end of the tracks in Fremont, and a number of excessive speed situations)(the last batch of cars from Rohr were delivered without train control equipment, this was installed and designed by BART 's own shops).
By 1977 the state Public Utilities Commission (PUC)was demanding changes be made or the PUC would pull BART 's operating certificate. This also resulted in a change in BART management.
The worst was a train fire in the TransBay tube that killed a fireman.
On the good side, when the line was built thru downtown Oakland it was recognized that the system would eventually need a third track. It was decided to build the right of way for the third track when it would be needed in the next century(the tracks were laid in the 1980's). A system designed for a minimum of staff. During labor actions on more then one occasion a minimal service was maintained with supervisory and management staff.(the system is too big to do that today). A fare collection system that does not need station agents to handle cash. Oh yes and an automated train control system where nothing can go wrong go wrong go wong g won g an. . . . . :-) (-: :-0
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