Passenger Trains > "I'll Take The Screeching Of The Wheels Over..." ( BART

http://www.sfgate.com/cgi-bin/article.cgi?f=/c/a/2009/12/23/MNB41B8420.DTL&tsp=1

Yeah that's all we need on BART in the tube under the bay...people SCREAMING into their cellphones to overcome the noise of the trains...which is just horrendous in the tube. As the system has aged and I suspect with not enough wheel and track maintenance done the noise level has gone way up. Sometimes I think I'm back on Caltrain running an F40! I've pulled my old Amtrak custom fitted ear plugs out of retirement and try to remember to take them with me every time I'm heading to the city on BART. I'm amazed their aren't more complaints about the noise although I suppose most younger people (like us older railroaders!) have lost much of their high frequency hearing already, thanks to loud music.

BART uses an old wheel/rail interface design with cylindrical wheels instead of tapered wheels. Tapered wheels tend to steer cars and avoid wheel flange contact with the rail on tangent track and broad curves (e.g. up to about 2 degrees). BART's designers (in the 1960s) were concerned that too much taper in the wheels would result in "hunting", where cars oscillate back and forth between the rails so they make the decision to go with cylindrical wheels.
Almost all other railroads and transit systems use tapered wheels, and handle hunting with appropriate suspension design and damping. From what I have heard BART was, in the early 1970s, considered the leading edge of future engineering. Probably true, but that was over 3 decades ago and the state of the art has moved on.

SEPTA in Philadelphia uses cylindrical wheels on their trolleys -- at least they did a few years ago. Sometimes it feels like the trucks hunt anyway...

> From what I have heard BART was, in the early 1970s, considered the leading edge of future engineering.

In that era my father designed some track geometry/measurement cars for several railroads. I remember him going on and on about how much more modern the engineering was on BART than any other road in the country, and giving considerable examples of things that it appeared they had done right. (And a few it was obvious they had done wrong.)

So yes, I can say that people considered BART to be prety advanced engineering. They also considered that it was prototype engineering, and the good and bad would have to be filtered out in subsequent generations of technology. Not that there have been subsequent generations in the US to speak of, but while we had hints that would happen in the 70s, it wasn't yet assured.

> Probably true, but that was over 3 decades ago and the state of the art has moved on.

Agreed. Although note that flat tires will hunt (or bounce about) too unless you have absurdly small clearances between the railhead and the flange. My memory is quite hazy on this, but I think that was what BART tried to do. I vaguely recall something about a spring-loaded design to keep the flanges in contact with the rail, but that might not have been BART.

Loren