Dr. Lowson,

We are faced with another one of those mass Internet phenomenas. I could have
guessed that "reversion wars" would happen. What I have not experienced is the
reality. I am going to suggest that we request volunteers to make the changes
that you have suggested, after carefully reading the guidelines that Ray has
provided below. I have added a few names to this cc list. In fact, I am
forwarding this (edited) discussion to the very public SeattlePRT list for their
edification and possible interest.

Perhaps this will be one of those things that just takes care of itself due to
the vigilance and persistence of various members of the Internet public.
--
Bob

Ray Van De Walker wrote:
> Bob, I appreciate the care and concerns of yourself and your
> correspondents. I confess that as a biomedical software engineer I am no
> more than an interested amateur on the topic of accelerations and PRT.
> I definitely want to be on the side of the angels, and I think a revert
> war could not serve the public interest, so I'm glad to discuss this,
> even though I'm not, by far, the only one involved.
>
> So let's talk about ways to fix the article.
>
> First, the topic under discussion is emergency stop accelerations. It
> should be clear from context that these are not operating accelerations.
> (if not, a sentence will fix it).
>
> It seems to me that that a PRT's emergency stop
> must decelerate substantially more than a train, or PRT is as
> impractical as some of its opponents allege.
>
> Therefore, the topic is useful, whatever the conclusion, because it
> addresses a point of feasibility. Since it addresses feasibility,
> removing the topic would almost certainly cause reversion.
>
> If true, its conclusion should be retained. If the conclusion is false,
> your correspondents should consider putting such a proof in the article,
> otherwise other PRT enthusiasts may revert it.
>
> Since the issue is quantitative, comparison values should be provided.
> Thus, alas, one of the standard Wikipedia compromises, omitting
> contested details, is not really practical. If values are
> omitted, engineers in the community are likely to recalculate and
> reinsert them. This is very likely to cause a future revert war on the
> same topic, even if all the correspondents have changed.
>
> I'm glad that someone has research on the topic of unrestrained
> passengers. I hope they will feel free to put it into the article,
> labelled as such, with public references (the community will check them,
> and contest them if they are not public). I used Gs in the article
> because it's an encyclopedia, and most readers have intuitive and
> mathematical experience with Gs or weight, but not with meters per
> second per second. The 6Gs for unrestrained passenger may just be
> wrong; it's a quote from an early version of an article on the unimodal
> web site. If anyone has better information, put it in, with references,
> and it will probably stick. The people who care will check the
> references and accept them if they are authoritative.
>
> I'd certainly accept a moderate emergency stop acceleration, labeled as
> a "conservative", "responsible" or "accepted practice". Since this
> increases the information in the article, I wouldn't expect it to cause
> controversy.
>
> However, a mild, practical value will not satisfy everyone in the
> community. A higher emergency stop deceleration directly increases
> the value of a PRT system, and Wikipedia is inhabited in part by
> partisan extremists. Therefore, in order to avoid a future revert
> war the article must address a safety engineer's knowledge of human
> limits. The community reads and knows everything, and over time
> compares everything to everything. I'm not an expert, but a reader is
> going to be... and you know how stubborn experts can be, right?
>
> It's normal in the Wikipedia, for the sake of NPOV, to avoid revert wars
> and to explain the full scope of a technology, to add a "radical", "as
> high as" or even "irresponsibly dangerous" view or alternative if it is
> at all technically feasible (truth trumps responsibility). Basically,
> this keeps reversion down. I chose 30Gs with torso restraints because
> Col. Stapp's work is well known to the community and it's also an
> accepted standard for crash mitigation in small vehicles. That is, it
> is a very conservative and socially acceptable (widely deployed) maximum
> deceleration for an emergency in a transportation device.
>
> I think the solution is probably to add an explanatory paragraph to the
> article that deprecates high G emergency stops. It should explain the
> real physical limits and the real concerns with approaching those
> limits. Some red herrings have already been reverted on this topic:
> "Wheels don't have enough traction" (PRT systems often don't brake by
> wheel), "The guideway isn't strong enough" (the revision said that mild
> steel is supposed to have 30 kpsi of tensile strength, so a few square
> inches of cross section of braking rail should be enough) "People won't
> wear seat belts" (So, the revision said that vehicle management systems
> can increase the headway and charge more; clever, I thought)
>
> Best wishes.
> Isn't the Wikipedia interesting?
>
> */Bob Dunning <cliff@...>/* wrote:
>
> Hi Ray,
>
> Some of us have some concerns about things being said in the Wikipedia
> article on PRT. If you would like some help making corrections or adding
> material to the article, please let us know. We are very interested in
> making sure the article is as accurate as it can be. If you are no longer
> actively involved in development of that article perhaps you could direct
> us to the people who are involved.
> --
> Bob Dunning
> President
> Advanced Transit Association
>
> Martin Lowson wrote:
> > Bob and Colleagues
> >
> > The Wikipedia free Internet encyclopedia
> >
> >
>
http://en.wikipedia.org/wiki/Personal_rapid_transit#Route_capacity-_strongly_aff\
ected_by_superior_braking
> >
> > contains the following statement on PRT
> >
> > "However, unrestrained (this is not a misprint) /sitting/
> passengers can
> > tolerate emergency stops at 6 gravities (59 m/s²), a deceleration
> like a
> > more exciting roller coaster. At 6 G (59 m/s²), 70 mph (115 km/h)
> > vehicles stop in 0.52 seconds, about 27 feet (8 m). With seat belts,
> > people easily tolerate emergency stops of 16 G (157 m/s²). With torso
> > restraints, people tolerate 32 G (314 m/s²) emergency stops,
> permitting
> > 0.1 second stops and 11 foot (3.2 m) safe inter-vehicle
> distances. Since
> > PRTs have sitting, perhaps belted passengers, and can have automated
> > emergency braking against steel guideways, some designers plan safe
> > emergency stops as short as 2 to 3 meters."
> >
> > I am interested to know if any of you agree with it.
> >
> > I believe it to be seriously wrong. Our own tests show that the peak
> > deceleration for unrestrained seated passengers is 6 m/s/s ie one
> tenth
> > of the quoted level. Even at this level some of our older female
> > passengers (eg my wife) were thrown to the floor. At the deceleration
> > levels quoted such passengers would simply continue out through the
> > windscreen.
> >
> > I suspect that whoever wrote this got confused between 6 m/s/s
> and 6 g
> > . In combat aircraft pilot are known to pass out at 6 g , which
> is why
> > they wear pressure suits to restrain the blood from draining away
> from
> > the head in high g maneuvers. Even then pilots only approach a
> peak 9g
> > in combat maneuvres
> >
> > A quote from John Stapp's biography (who did the pioneering work on
> > rocket sledges) follows
> >
> > "Within a few weeks' time, Stapp began to vary the number of rockets
> > used on the sled, and tested various braking configurations. The idea
> > was not only increase the G forces involved, but vary the "rate of
> > onset" ­ the time it took for forces to build to a maximum ­ and
> their
> > duration. By August 1948, Stapp had completed sixteen runs, surviving
> > not just 18 G's but a bone-jarring, jaw-dropping 35. And he felt
> he was
> > still far from any kind of limit.
> >
> > But while his first run had involved "no unpleasant sensations", the
> > later runs were torturous. Even at low Gs the straps of Stapp's
> harness
> > dug painfully into his shoulders. At higher ranges of
> acceleration and
> > deceleration, they cracked his ribs. Over the course of the tests at
> > Edwards, he suffered a number of concussions, lost a few dental
> fillings
> > and dinged his collarbone. On a couple of other occasions, he
> broke his
> > wrist. Being a physician and a bit of a stoic, he set one fracture on
> > his way back to his office.
> >
> > Out of all the things Stapp was subjected to, the most disturbing
> > (concussions aside) was blurry vision, which he began
> experiencing while
> > facing backwards at speeds above 18 Gs. The cause was intuitively
> > obvious. Blood was rapidly leaving his eyeballs and pooling
> towards the
> > back of his head in response to gravity, resulting in a "white out."
> > During later tests, when he faced forwards and the blood was
> pushed up
> > against his retinas, Stapp would experience "red outs" caused by
> broken
> > capillaries and hemorrhaging. Clearly, when it came to G forces
> the most
> > vulnerable part of human anatomy were the eyes. "
> >
> > I dont feel we should plan to subject PRT passengers to this (and
> even
> > if this were planned there is the non-trivial problem of
> designing the
> > rest of the vehicle to absorb these extremely high g loads)
> >
> > On the assumption that you agree with my view of this rather than the
> > Wikipedia version I suggest that one key objective of ATRA should
> be to
> > remove stuff like this from the public domain, where in my
> opinion it is
> > just as, and perhaps even more, damaging than the roadkill site
> >
> > Your views would be welcomed
> >
> > Martin