- The Elixabeth Line runs 24 trains per hour automatically through a 10-station tunnel in central London. It mainly uses axle counters to measure where the train is.
https://www.railengineer.co.uk/controlling-the-elizabeth-lin...
> The signalling is essentially hands off and is timetable driven. The latter includes GoA3 reversing moves at Paddington and Abbey Wood which are fully automatic as are all entries into and out of a depot. The line uses axle counters for secondary train positioning information other than where neutral sections for the overhead power exist, where track circuits are deployed, these being seen as less vulnerable to any spark interference from the overhead catenaries.
- It's kind of annoying that they don't go into specifics about why this is good. The problem with traditional accelerometers is that the error accumulates, and so even small errors accumulate. The article doesn't really address what makes this different - and in fact I don't think it is different. You're still just measuring acceleration using a sensor and that sensor will have errors that accumulate. So the question is how much better is it?
I would wager that actually this is probably just a way of funnelling money into research around quantum rather than genuinely trying to solve this specific problem. This specific problem sounds like it could be solved for a lot less money using conventional accelerometers in combination with some other local location data (optical sensors for example, you're in a very controlled environment).
by wiradikusuma
2 subcomments
- Don't trains run on a fixed path, meaning we can use more traditional "positioning systems" like, umm, math? Or placing passive sensors or paint a big number on the wall?
by readbeard
1 subcomments
- Cool technology, but seems a bit of an extreme effort just to check train position. Why can't they just use markers on the tunnel walls (or under the tracks)?
by wewewedxfgdf
1 subcomments
- You might be at Victoria Station, but there's a slim but tangible chance you are in fact in Paddington.
We won't know until someone looks at you. Until then you are on every station possible in the underground sorted of smeared out into a probability wave.
- Quite a dumb application of quantum physics. Cooling something to near zero, which takes energy, and is complex, and big, in order to obtain precisions which are magnitudes higher than what is necessary. As if one would use CPUs to prop up an uneven table and would boast that they use microelectronics.
"Instead of relying on conventional sensors, these devices use clouds of atoms cooled to near absolute zero. At those temperatures, atoms start to behave strangely — acting as both particles and waves. As the atoms “fall” through a sensor, their wave patterns shift in response to acceleration. Using what’s effectively an ultra-precise optical ruler, the system can read these changes with extraordinary accuracy, without needing satellites at all."
by ChocolateGod
2 subcomments
- If you have fixed beacons with a known location, couldn't the devices work out their location?
Seems like an engineered solution to rely on "quantum".
- In the end, it's all a series of tubes.
by maxwellsdeamons
1 subcomments
- 1.25 millions doesn’t even buy you the laser to cool the atom gas.
It’s for sure interesting, but to put this on a train, we will have to solve a few more questions. like for example, how do you operate an optical table on a bumpy metro.
- This is a weird application for such sensors. The train may be used as a test platform. DARPA launched a program to develop quantum sensors that are reliable outside the lab recently [1].
[1] https://www.nextbigfuture.com/2025/10/darpa-developing-quant...
- > As long as the vehicle has a known starting point, quantum accelerometers can continue tracking its movement accurately, regardless of what’s happening above the atmosphere.
So this is a much more precise inertial guidance system replacement? If true, I'd expect UK MoD to be involved to the point of making technology a military secret, but clearly it didn't happen.
- Considering the popular image of quantum mechanics, i m not sure people would want to be "schrodinger's passengers". It's unclear how reliable is the system in the long term
- The title is more than a bit of a stretch, but interesting none the less.
by 1970-01-01
0 subcomment
- I would put money on it using dead reckoning and tunnel markers. Quantum technology isn't something you can hire the lowest bidder to repair or upgrade.
- I would have thought a simple device that counts the number of times the wheel has rotated would be vastly simpler and cheaper, and surely accurate to within a few centimeters.
- Trivially solvable problems held back by entrenched bureaucracy. Needs 10.000 raspberry pis not quantum.
Anyone here could solve this overnight with todays tech.
by 123pie123
3 subcomments
- Call me sceptical, but I suspect if this works very well it will be used in weapons.
Which then leads me to think the whole thing is a smoke screen, not sure why
- I looked into quantum inertial navigation a while ago because I wanted to understand - is it some weird quantum thing where they eliminate all accumulated error or not. As far as I could tell the answer is "not" - it's just a very very precise way of measuring acceleration.
Seems kind of hard to imagine that any accelerometer can be so precise you can use dead reckoning to the centimeter over a long time scale. Especially given how strong acceleration due to gravity is.
- I always wondered if they could use good LiDAR and SLAM to determine location.
- This is very cool and very overkill.
- Sounds like a grift with the only redeeming quality of advancing technology perhaps useful elsewhere. There's no way encoders on wheels with resets on stations/junctions is not enough for precise train positioning.
- The train now approaching platforms 1 and 2 is the…
- At the risk of being näive, Why Tube trains are still a thing?
I want underground mini buses, optimizing their stops to the passengers' inside. Most of we passengers go to hub stations.
Tubes are like a 100-year old tech without remarkable changes.
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