On 06/15/2010 08:41 AM, danmitch wrote:
Ignoramus9619 wrote:

Dan, awesome post, thanks a lot for educating me.
You are quite welcome.

Train air brakes are a very complicated affair. Due to the long length
of the train-line, a delay exists between the action of operatign of the
valves in the locomotive, and the actuation of the braking action at
each car. The longer the train, the greater the delay toward the back of
the train. Hence the engineer must anticipate actions ahead of time.
This reqires experience, and a prior knowledge of the "profile" (grades)
of the track being operated over. Incorrect brake operatin can either
break the train in two (breaking couplers or pulling drawbars), or
result in a loss of control of the whole train.

Some work is being done on "electric" brakes for trains (probably still
air actuated, but electrically controlled) ... these would have faster
response to commands, but the technology is yet unproved. Air brakes,
while complicated and smoetimes troublesome, are a proven technology.
So, there's some resistance to change.

I had a guy working under me who's previous work had been for his dad's
company, building one of those electronic train brake controllers.

_He_ felt the technology was quite well proven! His father had been
involved in discussions with the railroads to incorporate the
technology, and it wasn't falling to performance concerns, it was
falling to compatibility, logistics and economic issues.

Even with a technology that's known to work, there's a huge barrier to
adoption -- For an electronic system to work you'd have to equip every
damn rail car with it, which means a huge retrofit and scrap expense.
the Westinghouse air brake is technically inferior* to the
electro/pneumatic systems, but it is standard on damn near every rail
car in the US. Try to put a train together with an electric brake, and
the first time you slot a car in there with a pneumatic-only brake
you've just broken the system.

Imagine the difficulty you'd have with trying to pull a rail car from
the pool when the first question you have to ask is "does it have the
new brakes?". Every time -- if you were putting a train together with
electric brakes, you'd need _all_ electric-capable cars; if you were
putting a train together with pneumatic brakes you'd want to save the
electric-capable cars for the electrically braked trains. And what
happens if you have a rail car sitting there, full of lucrative cargo,
waiting for a train that it can be slotted into? "I'm sorry sir, your
car is the wrong flavor for the trains coming through." -- how many
times do you tell a customer _that_ before he starts calling the
trucking companies?

I suspect that there was some of this resistance when the train
companies went from the old mechanical brakes to the Westinghouse
system, although in that case the rail car pool was not as developed (if
it existed yet at all), and the Westinghouse system would have held more
technical and economic advantages over the mechanical brakes than even a
perfect electro-pneumatic or fully electronic system would hold over the
Westinghouse.

* Well, except maybe for those pesky maintenance issues.

--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com