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Comment by marbletiles | Hacker News Reader

> Operation of Class 377 train doors require a (GPS) signal to identify that the train is in a station to allow the Driver to open the doors. Effectively this prevents the doors being operated in error when the train is not at a station and as such is a safety feature of the trains.

Was there some epidemic of doors being opened outside stations that I missed? This smacks of a solution looking for a problem

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http://en.wikipedia.org/wiki/Selective_door_operation

The real, less trivial problem is only opening the doors of train cars that actually fit on the platform.

GPS was just a poor choice of positioning system. There are already widely deployed systems where what is essentially an RFID tag sits at a fixed point on the track between the rails and, when scanned, tells the train exactly where it is.

Guess they want to make sure that cattle won't ever escape again as they did here: http://www.bbc.co.uk/news/uk-england-cambridgeshire-11658110

There is no mention of cattle or cows in that story?

It's the passengers who are regarded as cattle.

British slang for passengers - "The train operating companies treat us like cattle".

Actually, cattle may get treated better...

You'd risk being arrested if you treated cattle the way passengers are treated on some British commuter routes.

it's more common that the driver opens the doors on the wrong side, or at a short platform opens all the doors instead of, say the first 8

Oh god, opening doors on the wrong side would be absolutely terrible in rush hour - people back away from the door they think will open, and squeeze a few people out the other side onto the live wire, or perhaps into the path of a train arriving from the other direction.

Why would it be an issue if you opened more doors than necessary?

I'm assuming that the edge of the platform will always match the edge of a car, and that it is not possible to board off-platform cars (otherwise they wouldn't be off-platform), and that there will be no people in the "off-platform" cars. Otherwise, how would they get off? It seems extremely inefficient to start the train just to move it half its length, then stop it again.

Some trains will have 8 cars but stop at some stations with only 4 cars worth of platform. The passengers heading to those station usually knowmto board the first four cars.

The difficulty arises when doors are accidentally opened for all cars at 4-car platforms.

No, the train does not move forwards by 4 cars, it simply stops, passengers board and alight from the front four (including a rush of passengers frommthe back four cars who forgot that their station is a four-car stop), then the train leaves.

Of course not. This was some government contractor taking the tax payers for a ride. They could charge $x more per train this way and just through in a shitty gps device. Things like this aren't accidents.

Surely you mean £x more. And you're wrong anyway, this is a standard feature to allow long trains to enter short stations.

surely there are restrictions opening while moving but while stopped seems a bit odd. Aren't they paying the driver to think, to know when to open or not open doors?

Reducing the amount the driver has to think reduces the potential for human error.

The potential, yes, but the risk of human error? Once you have reduced the amount of thinking the driver has to do, you start hiring drivers who aren't that good at thinking, and the ones that are good at it stop practicing it.

I don't have data showing it, but I think making the driver's work duller can make things less safe for his passengers.

Thinking about this some more, I still don't understand. If the goal was door safety, why not use the same release systems automatic trains (eg underground) have?

Yeah. It's a completely ridiculous idea. Almost as if the project manager had an idea and pushed it through without thinking about the repercussions.

If it's really a problem why not use the speedometer to figure out if the train is moving? Or why not use something like the MTA's wheel rotation sensors? The guy who wrote the signal code for MTA said that they use wheel rotations to calculate when to play audio messages in-train and in-station... those "There is a queens-bound train N stations away". It's a simple idea.

The article wouldn't load for me, but did it say anything about why they don't just require the train to be stopped for the doors to open?

Train might stop in places that aren't stations. Also different stations need the doors on different sides to open. Therefore its useful to know exact location of train.

GPS could still be used for that, but what is wrong with opening the doors in the tunnel not at a station? I would think that would be helpful in the case of emergencies where people need to get off the train between stations. If a driver accidentally pressed the wrong button they might want to check to make sure no one is outside the train when they drive off, but I would think that wouldn't happen to much.

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