• If the struck train had braked to a stop in the block approaching the occupied block at the station, the following train with ATO getting no code should have begun braking before the operator put the train into an emergency stop.  A de-energized on-board, not wayside, relay that failed to break contact for mechanical reasons could be the culprit.
• If the struck train had pulled up to its leader at the station, the approach block would continue getting no code to clear the restictive indication.  The following train would get the same restictive signal to brake to a stop before entering the occupied block.
• If the struck train failed to shunt the approach block track circuit, the following train would get the same restictive signal to brake before the operator put the train into an emergency stop, and would have done so at less than track speed.  A de-energized on-board, not wayside, relay that failed to break contact for mechanical reasons, "sticking," could be the culprit.

From: icrelic <icrelic@...>
Subject: [CHICAGOTRANSIT] Re: Automatic Train Operation
To: CHICAGOTRANSIT@yahoogroups.com
Date: Wednesday, July 15, 2009, 11:29 AM

 

--- In CHICAGOTRANSIT@ yahoogroups. com, "Adam H. Kerman" <ahk@...> wrote:
>
> At 8:44am -0500, 06/25/09, Dennis McClendon <dennismcclendon@ ...> wrote:
> >Larry M wrote:
>
> >>Anytime you have something like that that operates less than 100
> >>percent you are putting human lives into harm's way. Anythine less
> >>thatn 100 percent is totally unacceptable.
>
> >Surely you're not saying that manual train operation would be better!
>
> Larry's right, Dennis. Control systems in a railroad environment must be
> robust and reliable. False information is worse than no information.
>
> I changed your Subject to Automatic Train Operation, which is what WMATA
> calls its signal and control system, although I think the term is being used
> in a proprietary manner.
>
> I discussed this with a friend who had a bit of information. When operated
> manually, the speed limit is 15 mph. When I first heard about it, it was
> clear that the following train had collided at speed, not at 15 mph.
>
> The system reported that the block was unoccupied. When the operator saw the
> obstacle, she attempted to take the system out of ATO so she could apply the
> emergency brakes but couldn't disengage.
>
> On a steam road, shunted track circuits are used to detect the presence of
> train in the block. The wheels create a shunt. Only an energized track
> circuit reports the ABSENSE of a train, so when it fails, the block must be
> assumed occupied.
>
> ATO relies upon relays on board to report the train's presense. If this
> fails, the block is assumed to be unoccupied.
>
> Rohr told WMATA that the relays were good for 70 years, even though a
> railroad is a harsh environment and electrical and electro-mechanical
> components are never known to last that long. Rohr, itself, wasn't in the
> signalling business that long, and having gone out of business...
>
> The relays on the original fleet were problematic from the beginning and
> have been known to require replacement for a number of years. WMATA didn't
> have the money to replace them on the oldest equipment, and kept operating.
>
> In addition, WMATA operates longer trains today than the system's original
> design assumed. This changes the braking profile. Was the system updated
> with newer braking profiles? This may have been another contributing factor.
>
> CTA doesn't use this signalling system. But BART and MARTA do. I don't know
> how similar it is on the other two systems.
>
> Now, everyone pretend Al replied and told me I everything I just said is
> wrong.
>

Don't worry I happen to know he's on the other side of the world talking about that subject that seems not to be allowed here. You missed him at the APTA workshop on that topic at the Hilton last month!