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.
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"a
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.
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
Question do the original car have regenerative braking that would help power consumption ? Do they have to run in trains only of their equipment ?
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
BART saved one minute of travel time and uses half the trains that Key did.
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.
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.)
Interesting article from BART stating that water intrusion is causing major problems and repair will be major use of bond money.
[quote user=“droughtquake”]
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.)
[/quote above]
BART 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.
The rainforest is getting a lot of press in BART. Leaking tunnels Wonder how that compares to NYC ?