[londons_explore]

You can still brake - you just need (automatic) agreement of all trains behind you to do so.

You aren't allowed to brake 'as much as possible' anymore - instead the best you can achieve is 'the best the worst of the trains behind me can achieve'.

[garaetjjte]

If one train derails for some reason, then every single train on the line crashes in the greatest pileup ever. Great.

[londons_explore]

Thats already the case for carriages within a train.... And people are fine with it.

We're also fine with the risk of a derailment onto a neighbouring track with traffic going the opposite direction. We could have tech which detects that, but we do not.

[lqet]

> And people are fine with it

The thing you are missing is compartmentalization. A modern high-speed train can hold around 1,000 people. This is the maximum number of people that could die in an accident (ignoring trains on other tracks or people next to the tracks). What you are proposing is essentially a train of infinite length, with virtual (software) coupling between groups of carriages. But then there is no limit to the maximum number of deaths in an accident. If you have 50 high-speed trains all traveling in this virtually coupled manner, a single accident may cause 50,000 casualties. People would not accept this, and no sane policy maker would allow it.

Note that if you consider derailments into neighboring tracks, you still have an upper limit of 2 times maximum train capacity, in our example 2,000.

[corobo]

A train derailing onto another track would be a hell of a derailment

Take this incident for example https://www.bbc.co.uk/news/uk-england-surrey-68466494

Imagine that then resulted in "the following train then slammed into the derailed train, having been unable to stop in time"

[rjmunro]

It happened at the Clapham Junction rail crash in 1988: https://www.bbc.co.uk/news/uk-england-london-46509473

A total of 3 trains were involved.

[corobo]

Oh wow, I was 6 months old when that happened. (36y/o now)

Pretty decent track record if that's the most recent example!

Upping the ante: how much worse would that have been if there were trains following closer than braking distance in both directions.

Special note that the train derailed so severely in this incident after colliding with a train stopped in front of it.

I'm even less of a fan of OP's "braking distance shmaking distance" proposal with this example of why it's a bad idea!

[blibble]

one of the original tube line ATO systems allowed a train to enter a platform as another was departing

people did not seeing this and the system was modified to not do it

[danhor]

You could also characterize the maximum braking ability of the train in front of you and the minimum braking ability of your own train and determine the needed distance for any given speed based on that. This would of course be more complicated and probably be solved by only including broad categories of trains (i.e. only two sets of values for either passenger trains or freight trains).

[andbberger]

this is how CBTC works

[TylerE]

You also would need to consider the braking ability of the train BEHIND you.