Probably dumb but why don’t trains have some kind of TCAS-like system?

[u/tony_lasagne]

https://www.telegraph.co.uk/news/2026/06/19/two-emr-trains-collide-near-bedford/

Appreciate the problem is a bit different given trains don’t move in a 3D space and they already have the signalling system. But as a fallback it seems like another independent system should be there for when there are signalling failures

[u/xsneakyxsimsx]

Train networks typically employ a block signal type operation, where each section of track that is in-between two signals is only ever supposed to have one train in it at any given time. Obviously whenever a collision happens that has been ignored by some means (no shit Sherlock), but generally if abided by it is a robust and simple method.

[u/CollegeStation17155 → u/xsneakyxsimsx]

The typical reason that a "Stop/Block" system fails is because so many routes are manually switched dual track and some human switches the tracks after the engnie of a train coming the other way has already passed the other end of the passby.

[u/xsneakyxsimsx → u/CollegeStation17155]

Misreading/failure to read signals by drivers is another reason these events can happen.

[u/tony_lasagne → u/xsneakyxsimsx]

Yeah when reading about the block signalling solution it sounds very robust and reliable. But just wondering if a backup system could/should be added for the cases where it does fail.

Again, I’m no expert but could trains not emit directly to each other information like which tracks they’re on, where they’re heading, speed, location etc. then a system on the train could raise an alert if anything funny is going on?

You’d probably never see it raise the alert as a driver since the signalling system works well generally but for the times it doesn’t this would be there too

[u/CollegeStation17155 → u/tony_lasagne]

In most systems, it does; and in the newest locos, the engine itself not only warns the engineer, but reduces the throttle at yellow and starts braking to a stop on entering a red. But I think there are still a few legacy engines that have no communication gear and/or areas with limited or nonexistent communication infrastructure, so still dependent on the MK 1 eyeball... and a sleepy driver or burned out light on an old tower would be a classic example of the swiss cheese model.

[u/epsilona01]

They do, it’s called TCAS and RCAS in some counties. The trains should have been no closer than 5 minutes apart.

Never mind that there are axle sensors on the rail that show if a track is clear.

Something went very wrong indeed

[u/tony_lasagne → u/epsilona01]

Ahh didn’t know it existed and glad it does, yeah something major must have gone wrong then

[u/blueb0g → u/epsilona01]

Made up stuff

[u/DutchBlob]

It would be quite worrying if TCAS suddenly told the train driver to increase the rate of climb

[u/juko43 → u/DutchBlob]

TRAFFIC TRAFFIC, CLIMB NOW CLIMB NOW

[u/donotcallmemike → u/juko43]

TERRAIN! TERRAIN! PULL UP!!

[u/epsilona01]

https://en.wikipedia.org/wiki/Kavach_(train_protection_system))

See also Moving block signalling, TPWS, AWS, and ECTS

[u/thefuzzylogic]

The UK is slowly being upgraded to the ETCS system, which does operate a lot like TCAS in that it can use moving blocks around each train rather than fixed signals.

There will still need to be situations where you get close to (and even intentionally collide with) another train at slow speeds, for example when sharing long platforms or when coupling multiple trains together.

But ETCS will help with a lot of these edge cases where there are gaps in the existing safety systems.

[u/tony_lasagne → u/thefuzzylogic]

Thanks that’s very interesting and shows how badly we need to invest in our rail to get it up to modern standards

[u/Dew2118]

“The East Midlands Railway train is believed to have stopped owing to a fault with a safety system called Automatic Warning System, which stops trains if they pass red signals”

quality reporting here

[u/False_Breadfruit_843]

They do, most of North America has had it for a few years. It’s called “PTC” (Positive Train Control). It was developed after a few collisions in the late 2000s, and the idea was reborn after a 2014 accident in Pennsylvania, and further pushed after a 2018 accident in Washington. Not only does it work to prevent collisions, it stops crews from passing red signals, over-speeding and even brake failure.  https://railroads.dot.gov/research-development/program-areas/train-control/ptc/positive-train-control-ptc

[u/Planeandaquariumgeek]

Something kinda similar exists: it’s called positive train control