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Comment by lbriner | Hacker News Reader

Because of signal sighting rules in the UK, we experienced a lot of trouble upgrading lines to higher speed. All of a sudden, that signal that you could see for 10 seconds could now only be seen for 8 due to a bridge or whatever. Muchos dollars relocating signals and in some places not being able to increase the line speed at all.

Boring but very real reasons why we "can't just update things"

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Dunno why they don't just go ahead and bite the bullet and go to 100% in-cab signaling. The technology has worked for decades and has been deployed on many lines, including a few in the UK.

Cab signaling requires a different set of standards in order to provide the necessary level of safety.

Cab signals are (usually) transmitted through the rail and picked up by a special receiver on the leading axle of the locomotive. Each locomotive has to be equipped and the rails themselves have to be checked and blocked. This also means the rails have a higher maintenance requirement as opposed to lineside signals which can be more easily maintained.

However, some countries (Brazil predominantly) have embraced a GPS based cab signal system where lineside signals are almost totally eliminated. However, this was done with federal subsidies to cover the expense iirc.

Another example is the US Northeast Corridor where cab signals are used along with lineside signals to provide a level of redundancy at speed.

Unfortunately there’s no easy solution, but I lean towards the Brazilian GPS based systems from Wabtec.

As a random piece of trivia, in cab signaling was pioneered in the 1920's and implemented commercially by Pennsylvania Railroad the 1930's while upgrading their main line between New York City and Washington D.C. You can see in this photo that the engineer had one indicator that would light up for each signal aspect: https://i.pinimg.com/originals/31/85/83/3185833fba11b79498ff...

Realistically, in the UK, it's going to be ETCS with balises: all new build stock at this point either has ETCS in-cab signalling fitted, or is designed for its fitment.

That said, the rollout of the infrastructure side of ETCS is somewhat delayed, but it is happening in places (Thameslink is ETCS Level 2 with conventional signal overlay, albeit with shorter blocks in ETCS; Crossrail is ETCS Level 2 with no overlay).

You'd have to upgrade all the rolling stock as well. That's not always possible, for technical or financial reasons.

The locomotives, not all the rolling stock. I'm not saying it wouldn't be hard/expensive, but it seems better to spend money on things that will be useful for decades rather than stopgaps that just kick the can a little further up the road.

You're right of course, just the locomotives.

If budgets always allowed us to do what's best over the next decades the world would probably be a much nicer place.

But when the people who hold the pursestrings are looking no further ahead than their next election, "useful for decades" means nothing at all to them.

If you remove the block signaling system and use in-cab signaling, you still need to know where the back of the train is. Otherwise a train could run into the back of another in the fog or heavy rainstorm. Currently, railroads use FREDs (flashing rear end device) on the last car of the train. Some FREDs are more intelligent than others but would benefit from being able to send out their location via GPS.

https://en.wikipedia.org/wiki/End-of-train_device

Longest trains are under five miles so you could use that or whatever the limit for that line is as a safe baseline. Unless you're worried about trains separating.

You are worried about trains separating.

Even more if you have distributed power. A train can separate, and both halves can keep moving.

That's not an actual problem. You simply have 2 trains each broadcasts it's location. It's unexpected separations that might be a problem, but those are currently very rare and dealt with seperatly than static signals.

It's like you need to design a nuclear reactor to deal with an aircraft hitting it. You don't need to automate the response becase that's a rare situation.

Plus with an actual separation the brakes will dump anyway and things will stop... well, not fast, but as quickly as they're capable of.

Well, I read about one instance where it happened, and the brakes didn't apply. (Not sure how that could happen other than a mess-up in building the train. You'd just about have to have both angle cocks closed.) Both fragments continued, for miles.

Can't cite a source (I think I read about it on the Altamont Press discussion board). And that's only one instance. And it could have been reported incorrectly. But it appears to be possible for this to happen.

You can use block signalling with in-cab signals.

Pretty sure all the In-Cab systems still have axle counters and track circuits.

Most British passenger trains are multiple units (and most British trains are passenger trains), so there's effectively little distinction between locomotive and rolling stock.

You have a cab at both ends. In between are just slave units. No cabs, even if they have motors.

it's normal for a train to be made up of multiple independent units[1], which are then coupled together to make a longer service

each unit has two cabs (one at each end)

a common configuration is a 12 coach train made up of 3 x 4-long-units, which would have 6 cabs

that's a lot of upgrading

[1]: http://extra.southernelectric.org.uk/news/southern/img/colin...

[2]: http://extra.southernelectric.org.uk/news/southern/img/colin...

And not all locomotives, only the new one that reach speed where the signal is not visible in the given timeframe.

And of course there's the whole discussion in the UK about having a second safety-critical person on the train (e.g. "guard", "train manager" etc.) versus driver-only operation.

The DOT here just updated the signaling at some road intersections and I've really appreciated the better visibility.

How about using some sort of advance signal?

There are repeater signals for this purpose, see http://railsigns.uk/sect7page1/sect7page1.html

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