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)?
> Naturally, trains already have track-based location systems, but they are usually based on a train being within a “moving block”, so their accuracy is down to metres rather than centimetres. If you want to monitor track conditions, the more accurate the location of the suspected fault, the less time staff spend repairing it. Agree in principle though, is this extreme precision really needed?
The lines with platform edge doors (Elizabeth, half of Jubilee) do need to be in the right place with 10-20cm accuracy.