The entrance to the tunnels isn't where the interference of happening. The tunnels start at Liverpool Street

What's a bit strange is that they've been running the same trains with passengers on from Liverpool Street through Stratford for more than 2 years, with passengers, as TFL rail. But I guess they had to upgrade the signalling around Stratford to work with the trains coming through the core, and that is still buggy

The entrance portal is at Pudding Lane:

https://anonw.com/2021/08/12/the-crossrail-tunnel-portal-at-...

From there the train will travel underground to the Liverpool St - Moorgate station.

There’ll still be Elizabeth line trains travelling into Liverpool St station but there’ll be terminating.

Fun fact there’s the large ABBA venue going up at Pudding Mill Lane.

https://www.ourbow.com/abbas-virtual-comeback-show/

The things one misses when not commuting.

No one has called it the ABBAtoir yet, but I’m waiting to see who’ll be the first to come up with that name.

> The entrance portal is at Pudding Lane

I think you mean Pudding Mill Lane?

Pudding Lane was where the Great Fire of London started.

The tunnels do actually start immediately to the west of Stratford station, around Pudding Mill Lane. The new line follows a different route from the existing main line into Liverpool Street - meeting up with the other branch in Stepney and then via the new station at Whitechapel. When trains start travelling through to Paddington they will take this route.

This means that the boundary between the mainline signalling and the new CBTC signalling in the core is at Stratford. But this only applies to trains taking the new route; services on the existing GEML/Shenfield Electric lines continue to use mainline AWS/TPWS signalling, which is why there hasn’t been any impact on services to date.

You're right. I should have realised it couldn't follow the same line, because I knew about the new stop at Whitechapel.

The current service is to Liverpool Street high level, staying on one signalling communication system. The problem is about changing to a different one for the core (which includes Whitechapel before Liv St). They had a similar problem on the other side but it was resolved easier.

Only the self-contained Paddington to Abbey Wood core section will be part of the initial opening.

Trains from Stratford will still be terminating at the same high-level platforms at Liverpool Street. Through running into the core tunnels (and thus a signalling system change) will come later.

it's quite amusing to hear Liverpool Street's mainline railway station described as high level when it's buried 30ft underground

it was originally buried so that it could connect up with the Metropolitan Railway (today's metropolitian line on the London Underground)

this was so that in 1875 the Met could use the mainline railway station as terminus (whilst their own was under construction)

The low level is buried 34m underground. https://www.crossrail.co.uk/route/stations/liverpool-street/

If they're struggling, they should put a shout out to UK radio hams to help diagnose the problem, they'd get loads of expert help.

Or maybe use something that's less dependent on radio frequency in one of the most populated, thus most frequency-polluted areas on Earth. Radio not always is the best choice, sometimes, cable is worth it.

The issue is interference at the interface between the train and the fixed signalling system.

I’m sure you can appreciate the impracticality of building a train to signalling system interface that uses cables!

Shouldn't systems Like LZB or ETCS bei mostly protected against radio interference as only the Last section (centimeters) needs to bei transmitted wirelessly? Are they used in the line or did they opt for something else?

Yeah, generally that’s true - it’s certainly not a long-range system. I’m not clear on what the actual problem is at Stratford, but I do know these systems can be quite sensitive and it can be tricky to ensure they operate reliably alongside each other.

In the case of Crossrail the core (new tunnels) use CBTC signalling, I think based on Siemens TrainGuard - I think the specification of the project predates ETCS being proven as a viable solution for this particular kind of service. The services leaving Stratford to the East use TPWS/AWS in common with most services on the UK mainline network.

The challenge is in the transition between the two systems, as I understand it - anything out of the ordinary and the train will of course come to an immediate halt.

LZB uses cable loops.

ETCS can use cable loops, but for full functionality a radio data connection is required.

At first blush I can but thinking a bit further, these are electric trains right? And I know there have been "use your home electricity wiring for network" things around for decades...

So can't they use the power cables for comms?

It’s an interesting idea and not without some merit. Some signalling systems do actually use the rails as a conductor already, although that’s just basically “is there are train on me or not” detection.

I’m getting out of my depth, but I’m sure I’ve seen at least one signalling system that uses the track circuit as a data signalling channel to the train to provide in-cab signalling, so I’d guess it’s at least theoretically possible.

I’d imagine it would have much the same challenges as radio in practice though - interference from poor connections and ambient noise, not to mention your channel is basically a massive antenna.

You’d have to keep plugging it in.

Are you assuming radio hams are better at this than engineers getting paid for it?

No, but I am assuming that in their multiplicity and range of interests, they might quickly stumble on a solution in a way which a smaller population of well-trained professionals wouldn't.

Reminds me of Feyerabend's "Against Method".

When I lived in Stratford I always had lots of really weird intermittent problems with WiFi and 4G. Probably not related but would be interesting if it was