> A more advanced system would aim to have trains as close together as cars are on a freeway.
https://en.wikipedia.org/wiki/European_Train_Control_System#...
https://en.wikipedia.org/wiki/European_Train_Control_System#...
As long as you have comms with the trains around, it's clearly possible to safely go less than the braking distance, as long as you can be sure of the behaviour of the train ahead, even in the case of an equipment failure (ie. in case of a power failure, it will not slam the brakes on, but decelerate at X m/s^2).
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'.
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.
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.
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"
A total of 3 trains were involved.
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!
people did not seeing this and the system was modified to not do it
Also, I don't think it's ever safe to be closer than braking distance because the bahavior of the train ahead is never guaranteed. There's always a chance somebody parks their car on a rail crossing or some other sudden stopping-event occurs.
It is a tradeoff between the safety of lives on board and traffic requirements that is relatively easier to accept when the average number of people involved is low against massive speed and efficiency gains.
The same cannot be said for trains though. Modern trains carry upwards of 1000 passengers, often at high speeds and without all of the safety and retention systems built into modern cars.
Having one or multiple trains with this large amount of people onboard be involved in a sudden catastrophic accident is possibly not worth the efficiency gained by thess than one minute separation.
Unfortunately we cannot just think about a normal scenario of simple deceleration
No. Unsafe drivers have illegally decided this, but in most jurisdictions it is your responsibility to stop your vehicle short of the one in front of you. You should be maintaining stopping distance from your vehicle to the one in front.
I am not so sure. In Germany, for example, the minimum required distance to the car in front of you is "speed in km/h divided by 2 in meters". So for 100 km/h, you are required to keep a minimum distance of 50 meters. I very much doubt that you can stop a car going 100 km/h within 50 meters.
The 50m is the reaction buffer, not the stopping buffer.
It’s also prudent to give more leeway to vehicles you can not see around to avoid the large truck swerving to avoid the refrigerator that just fell out of the truck in front of them problem.
Not to disagree, just throwing in a variable that trains don't have
You should be able to sing "Last night a DJ saved my live", which is a bit more than 2 seconds. I liked that, because it's one you can actually test for while driving.
I find it a lot harder to estimate 50m while driving at 100km/h
For a car traveling at 100Km/h the stopping+reaction distance would mean more than 130m, which is a quite large and possibly impractical for higher traffic scenarios.
highway separation is unacceptable for anything other than trams (which are slow and have track brakes). the path to safely increasing throughput is to increase braking performance and minimize dwell time. existing systems eg paris line 14 and the tokaido shinkansen have very high throughput.
transit projects would look even better compared to highways if they had to be safe too!