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Around where I live, we frequently have trains running that are way way longer than some of the platforms at stations - my local station for example has space for at most 6 carriages when trains can be anything from 2 to 12 long. All the modern units have their own variant of SDO, selective door opening
but they seem very overly complicated and/or inefficient.
Southern, operating Electrostar units, use a GPS system so the train knows where it is and releases the correct number of doors automatically (it's very slick), but has the problems that 1) if the system goes on the blink then it won't allow any doors to open, and 2) if the driver fails to stop in the correct place (ie doesn't go far enough along the platform) then trailing coaches may be opened with no platform alongside.
South West, using Desiro units, instead have the conductor move to the cab of the first unit that is not toally within the platform; releasing the doors from this cab only operates doors in front of the cab, meaning that in my aforementioned 6-coach station, only 4 will be available, and is also incredibly slow if the guard isn't on his toes.
So my idea is to put some form of indicator on the track in line with the platform area which the train can detect, and only doors that are above the indicator will release.
I pondered a few methods of doing this but many would be easily affected by things like snow. So, the option I think would work best would be an unpowered fourth rail, identical to the third rail power, but running in the middle of the track (like on the London Underground). Hardware identical to the conductor shoes could then be mounted on the coaches, under each door for maximum granularity. The shoe would either trip a mechanical switch when in contact with the rail (shoe rails slope down at either end so a shoe in contact is physically raised) or, if the fourth rail was electrically connected to the running rails, would be grounded, meaning it could be used for a direct electronic input.
Platform screen doors
http://en.wikipedia...atform_screen_doors
Not what this idea is about. [K o R, Feb 29 2012]
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you need to be an athlete to get on or off trains at Clapham Junction. Grrrrr. |
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po - Busiest railway station in Britain and yet it can't take 12-coach trains either! |
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Just open all the doors. Some passengers will plummet two metres onto the ballast, and die. |
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Eventually (in a surprisingly short time) selection pressures will weed out those rail travellers who are too stupid to ckeck if there's actually a platform there before stepping off. |
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Thus the problem is resolved, at no cost. |
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//many would be easily affected by things like snow// |
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Actually when I read the title my brain immediately turned up a lever at the base of the door, that would be tripped when the platform brushed against it. But yeah, snow might trip it too if there's enough of it. |
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Bun for something that's needed, and that you seem to have thought out better than I did. |
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8th of 7: Natural selection is good, unfortunately Elfin Safety don't approve of its usage. |
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Psalm: That's a more HB approach, certainly, but it runs into difficulties on things like curved platforms (sometimes there's a gap of nearly a foot between the platform and the door edge!). |
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//Psalm: That's a more HB approach, certainly, but...// |
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*Psalm_97 jumps up down excitedly |
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What's wrong with a simple laser or EM detector that
determines whether the door is adjacent to a platform or
just open air? It would be a bolt-on device, much less
expensive and maintenance-intensive than a third or fourth
rail with shoe. |
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[8th of 7], there are other pressures, not necessarily selective in the way you envisioned. Consider that in Japan they have guys on the platforms who have the job of squeezing as many extra passengers as they can, into the carriages, before the doors close. So, when the doors open again, at the next station, that pressure will want to be released. Those standing next to the doors may not have much choice, about exiting, regardless of whether they know a platform is present. |
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I was thinking of a simple sonar device interlinked with the door-opening mechanism. If such devices can be used to autofocus a camera (pioneered by Polaroid), then they should be able to notice whether a platform is present. |
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Sonar, even better than laser or EM! That way there won't
have to be a reflective strip along the edge of the
platform. |
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In the US, every rail car (passenger and freight) has an RFID
tag installed for tracking purposes. The weatherproof
casing is about 2" x 5" and mounts on a standardized
bracket; the platform detector could easily be contained in
a similar casing and mounted using the same style of
bracket, which would significantly reduce
manufacture/installation expense. |
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CJ is one of the busiest stations in europe for people with long legs and head for heights. |
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// Those standing next to the doors may not have much choice, about exiting, regardless of whether they know a platform is present. // ... and will therefore be eliminated from the travelling population. |
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Therefore, the numbers of travellers will decrease. |
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Therefore, the trains will be less crowded. |
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Therefore, the "pushers" will no longer be needed, since the trains are less crowded. They can be made redundant. |
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Therefore, by doing nothing and allowing "market forces" to operate, there will be cost saving. |
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[8th of 7], fewer passengers could cause the train service to go bankrupt. Then what? |
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Unlikely; the Japanese government just unloaded their
passenger rail system onto the private sector, and I
imagine they'd turn themselves inside out to avoid getting
it back. |
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//fewer passengers could cause the train service to go bankrupt// |
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No, the force cited as picking these passengers off would diminish in almost logarithmic proportion to the number of passengers. And below a certain point this force would disappear completely. |
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// fewer passengers could cause the train service to go bankrupt. Then what? // |
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No, because the internal organs and other valuable parts of the "eliminated" passengers can be sold on the open market, providing a revenue stream somewhat greater than that ever delivered by said passenger's expenditure on travel tickets. |
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If the financial viability of the system hinges on the "overflow" passengers, then they have bigger problems than whether there is a platform. |
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Zip-lines.
Individual zip-lines. |
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It's really the only answer. |
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Alterother: You reckon a laser or EM detector is simpler to maintain than a switch that is mechanically tripped? |
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In all seriousness, the problem with using anything to detect the existing platform profile is that they are so variable. The idea of the rail is it's unintrusive, doesn't really require any maintenance (it's just a rail, nothing fancy about it) and works as a definite platform marker; likewise the shoes on the train are very simple: they drop by gravity if not over the rail, no springs, virtually no maintenance at all. |
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On the St. Louis Metrolink, the geniuses in charge put up fencing that was designed to keep people from walking off of the platform into the gap between cars (who in the world did this, I have no idea, as the lack of a roof or anything resembling a door should have kept people out of the gap, but whatever). |
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Conductors then had a problem with pulling too far forward or not forward enough, meaning that the fencing blocked a door on the leading or trailing car. |
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So they just put up a guidepost. It's a simple vertical black plastic tube that tells the driver "This is where you stop." Because they're vertical, there's no problem with snow accumulation obstructing them. |
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tl;dr: just put up some simple reflective tape on posts or on the walls every so often at the end of a station, depending on carriage length. Driver stops once, releases batch 1 of communting horde, closes doors, eases forward, releases batch 2 of horde. |
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If the trains could be smart enough to know where they were, they could also probably figure out how to program the doors for each stop. |
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// You reckon a laser or EM detector is simpler to maintain
than a switch that is mechanically tripped? // |
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Yes, because an electronic detector contains no moving
parts. In all the years I worked as a carknocker, the only
parts of a box car that I never replaced were the center-
sill (the big longitudinally-oriented frame component that
serves as the 'backbone' of every type of rail car) and the
tracking tag, and I'm not exaggerating. Every
mechanical device needs routine servicing and
replacement, especially on rail cars. Omniscient though I
am not, I'd be hard-pressed to name an industry that
abuses its equipment more than the railroad. |
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Worse: mining, particularly coal mining. |
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I didn't think of mining. I did think of the military, though I
don't consider the Armed Services themselves to be an
'industry', but I discounted it because one of the primary
functions of military equipment is to withstand abuse, both
incidental and deliberate. Two good examples, though.
The beating taken by railroad equipment is probably of a
similar caliber, especially freight cars. They really get
punished out there. I've refurbished cars that a layman
would swear had been in a wreck, but the damage was
simply accumulated by years of routine battering. |
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Yes, there are already markers on station platforms to tell the drivers where to stop. The device is to provide a much simpler means of automating which doors open without relying on the complex GPS system, or the inefficient limited door release. No matter where the train stops in the station, all doors that are alongside platform will operate. |
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[+] Several parking garages in my area use (what I
presume to be) a sonar device mounted over every
parking space to detect if a car is in the spot, and
turn on a red or green light accordingly. Why not
use something like that? They're cheap, fairly
reliable, and the devices and communication system
should be pretty simple to install/retrofit. |
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That might also be a pressure or magnetic sensor
embedded in the
floor, like those used at intersections with 'smart' signals.
Could work in this application as well. |
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I imagined that the platform-detecting doors would
be complemented by a platform-detecting giant
boot. The passengers wanting to alight gather
immediately inside a door; when the platform
detector is triggered, the door and boot are
triggered in quick succession, efficiently propelling
the passengers into a giant catcher's mitt on the
platform, thus eliminating wasteful stops. |
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The "simple system" this idea describes has been used for many years on elevators, hasn't it? The system doesn't change a great deal just because the cars travel horizontally... [ ] |
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Elevators work over a relatively short distance, are
completely enclosed, and are integrated into the
"track" in a way that trains cannot be. You can't
have more than one elevator per shaft, elevators
cars can't run in a continuous loop (paternosters
excepted, of course), elevator cars are unable to
switch shafts in mid-transit, and so on. |
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...not exposed to the elements, not repeatedly bashed into
each other, not perforated by fork-truck tines on a weekly
basis... |
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Some (underground) train stations in Singapore have a tall barrier on the edge of the platform, fitted with sliding doors. When a train stops, its doors align with the platform's doors, and both open, allowing passengers to step through. I always assumed that sensors were involved, to prevent doors on either side from opening when not properly aligned, so this idea may be baked. |
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It seems to me that this whole problem is caused by the incorrect placement of doors on trains when, really, a means of egress is only required on the platforms (although I'll concede that there probably needs to be some sort of contingency for emergencies, perhaps a passenger ejection system). I'd go for a sliding roof section on the train which opens when stationary and some sort of articulated vacuum tube on the platform which can be lowered in through the gap to suck out passengers standing in the clearly marked & designated exit area. |
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Easier to have retracting floors, dumping the passengers into a basement chute. |
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//Worse: mining, particularly coal mining. |
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MUCH worse: The military//
Far, far worse: Exhibits at childrens' science parks. |
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spidermother: This idea is quite different from platform screen doors. They are to stop people from falling onto the track; a consequence of their use is that they have to be able to detect when a train is alongside and only open sufficeint doors for the length of the train. This idea is to allow a train of any length to stop anywhere along a platform and only those doors that are alongside the platform will be openable. |
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...which is a great idea and entirely possible, though the
actual mechanism that should be employed remains a topic
of heated debate. |
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Things like that make [The Alterother] happy. |
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I would use an industrial proximity detector beneath
the door to detect the metal edge in the platform.
Simple, reliable, tested. |
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haywardt: Unless the platforms aren't made of metal. Which ours generally are not (concrete and brick ftw. Wood in some cases - check out Berrylands some time). |
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//This idea is quite different from platform screen doors.// Yes, but I was assuming that the train itself has sensors, so that only those train doors that are adjacent to a platform door open. If so, they would constitute platform-detecting train doors. I realise that your idea is not exactly the same. Sorry for not spelling that out. |
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// Unless the platforms aren't made of metal. // |
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An adhesive metallic tape running along under the lip of
the platform would fix that. In fact, you could use the
same kind of tape that's made specifically to trip
industrial-use proximity sensors. |
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