On Thu, 2 Feb 2006, Mike Bristow wrote:

In article ,
Tom Anderson wrote:

Okay, so my solution is slightly facetious, but only slightly - i don't
see how opening the right number of doors needs to be terribly
expensive.

The testing required to prove a safty-critical piece of kit would, I
expect, be larger than you think.

I realise that it would be large - i just don't think it would be large
enough to be a significant fraction of the cost of the whole seven-car
project. I could well just be being wildly over-optimistic here.

Playing devil's advocate here - how safety-critical is this? I mean, the
least safe failure mode i can think of is the door being open, which would
leave the Jubilee in a similar state to every other tube line!

But I'm prepared to admit that I don't know all that much about runnin a
railway, and could be wrong.

Same here. But playing at armchair fat controller is a common past-time
round these parts!

[1] eg run with 6 doors that open at the Stratford end of all platforms,
and lock out the car at the other end of the train. On the flag day,
run with 7 doors that open on the platforms, and ban 6-car trains.

Good idea. I did wonder why this wasn't done. Maybe because of the risk of
people getting the cars unlocked, then being unable to get out?

tom

--
Better to die on your feet than live on your knees. -- Emiliano Zapata

In article ,
Tom Anderson wrote:
On Thu, 2 Feb 2006, Mike Bristow wrote:
The testing required to prove a safty-critical piece of kit would, I
expect, be larger than you think.

I realise that it would be large - i just don't think it would be large
enough to be a significant fraction of the cost of the whole seven-car
project.

Wrong question: the right question is "is the cost of $plan more than the
cost of $otherplan".

They had a plan: shut the Jubilee down for a week. It worked.
We're arguing over implementation detail (albeit important
implementation detail).

--
RIP Morph (1977-2005)

On Thu, 2 Feb 2006, 1089 wrote:

In message , Tom Anderson
writes

Not C++, Java - good god, you don't imagine i'd use a language with
manual memory management and pointer arithmetic in a safety-critical
system, do you?

Well, yes, actually, because you know what you have and can test and fix
every piece of it, rather than relying on an over-complicated
third-party runtime which has almost certainly not had adequate testing
for a safety-critical environment.

Depends on the runtime. And on what you're doing, of course - as
Greenspun's tenth law observes, any large program includes a
reimplementation of much of the functionality of an over-complicated
runtime, so you'll generally be better off using a more sophisticated
language to start with. If you're doing something fairly simple that
doesn't need much dynamic memory, C might be better; this example is
probably in the latter class, to be honest.

I'd rather be using C, or a Forth-type language.

Or Ada - still (usually) no GC, but at least much better type-safety.

Highly entertaining article comparing Ada, C, C++ and Java to the original
Ada requirements document (used as a gold standard for a language for
serious embedded systems):

http://www.adahome.com/History/Steelman/steeltab.htm

Ada wins, Java and C++ are neck-and-neck, and C comes in last. Mostly,
though, that's because C doesn't specify thread-related stuff as part of
the language; i think C + POSIX would do a lot better.

tom

--
Better to die on your feet than live on your knees. -- Emiliano Zapata

Tom Anderson wrote:

Playing devil's advocate here - how safety-critical is this? I mean, the
least safe failure mode i can think of is the door being open, which
would leave the Jubilee in a similar state to every other tube line!

Presumably the difference would be one of human behaviour. If people
are used to the doors opening on the covered lines meaning they can walk
through them then they may do so if this situation even though they
would never simply step off a normal platform.

--
To contact me take a davidhowdon and add a @yahoo.co.uk to the end.

Mike Bristow writes:
They had a plan: shut the Jubilee down for a week. It worked.

True. But if platform-edge doors were the issue, why couldn't they
have kept the line open from Stanmore to Green Park, using whichever
trains were available each day?
--
Mark Brader, Toronto | "You can write a small letter to Grandma
| in the filename." -- Forbes Burkowski

Mark Brader wrote:

Mike Bristow writes:
They had a plan: shut the Jubilee down for a week. It worked.

True. But if platform-edge doors were the issue, why couldn't they
have kept the line open from Stanmore to Green Park, using whichever
trains were available each day?

A better alternative for that week would've been to divert the trains of
the length that there were less of to Charing Cross.

A much better alternative would've been to lengthen all the trains
overnight! I'm sure it's something that they'd be capable of if they put
their minds and resources to it!

--
Aidan Stanger
http://www.bettercrossrail.co.uk