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Comment by adrianN | Hacker News Reader

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.

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

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

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.

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...

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.

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.

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

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