Emergency stopping brakes

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suzanneparis

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Trains take a long distance to stop.

In an absolute emergency, such as a situation when a driver can see that a terrible accident is about to happen, would it be possible for trains to have some form of additional braking system that brings the train to a stop quicker even if it causes damage to the track?

Could additional brakes descend from the carriages and grip the tracks on both sides for example - a kind of giant disk brake where the 'disk' is the track.
 
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notadriver

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Trains take a long distance to stop.

In an absolute emergency, such as a situation when a driver can see that a terrible accident is about to happen, would it be possible for trains to have some form of additional braking system that brings the train to a stop quicker even if it causes damage to the track?

Could additional brakes descend from the carriages and grip the tracks on both sides for example - a kind of giant disk brake where the 'disk' is the track.

German trains are fitted with magnetic track brakes
 

theageofthetra

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Tramway vehicles have extra track brakes for use in an emergency- has such a system been tried on heavy rail in the UK?
 

Deepgreen

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German trains are fitted with magnetic track brakes

Many tram systems around the world have emergency magnetic track brakes. On railways the higher the speed the more damage would be caused and injury would be possible to passengers owing to severe deceleration forces exerted during the use of track brakes.
 

TheEdge

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Surely if you have a mainline train, obviously several hundred tons so the forces are magnitudes bigger than acting on a tram so sort of mechanical/magnetic brake system would surely risk damaging track under a train causing a derailment and making a bad situation worse?
 
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Surely if you have a mainline train, obviously several hundred tons so the forces are magnitudes bigger than acting on a tram so sort of mechanical/magnetic brake system would surely risk damaging track under a train causing a derailment and making a bad situation worse?

You could always deploy a John Deere in front.
 

Deepgreen

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Surely if you have a mainline train, obviously several hundred tons so the forces are magnitudes bigger than acting on a tram so sort of mechanical/magnetic brake system would surely risk damaging track under a train causing a derailment and making a bad situation worse?

Indeed - it would depend on the speed and how many magnetic contact contact points were used - fewer contacts would place greater stress on those applied whereas a greater number spread along the whole train would smooth out the forces and give a reduced risk of track damage severe enough to derail. In any event, I imagine that the use of track brakes would require a minimum of a track inspection afterwards.

In some cases, an 'upright' derailment might be better than a head-on collision (or at least a much-reduced speed collision might be achieved). The crash in southern Italy today might have been a case in point, although I have no idea of the details there.
 
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Spagnoletti

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Rail passengers in the UK are not restrained at all and there are no systems to mitigate the effect on passangers of high levels of deceleration (eg airbags) so it might actually result in more harm by decelerating more severely. Railway vehicles have pretty good crashworthiness these days and provide a good survival space for the humans inside if they're not thrown around too much.

The fatality per passenger mile in the UK is pretty damn low so there is also the cost benefit to think of - how many deaths or injuries might be avoided by fitting such improved braking systems per £ spent? There are probably more cost-effective outcomes.
 

notadriver

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I once did an emergency stop from 70 mph. It actually pulled up really quickly in not much more space than a coach would have required.


Sent from my iPhone using Tapatalk
 

hwl

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Norway uses track brakes as a back up option given the snow and ice in winter that can effect the rail wheel interface.
 

Deepgreen

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I once did an emergency stop from 70 mph. It actually pulled up really quickly in not much more space than a coach would have required.


Sent from my iPhone using Tapatalk

Really - in what stock? I would imagine a road coach slamming the anchors on would stop at least three times as soon as a rail vehicle, given the huge friction/adhesion differences.
 

notadriver

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Really - in what stock? I would imagine a road coach slamming the anchors on would stop at least three times as soon as a rail vehicle, given the huge friction/adhesion differences.



I'm probably slightly exaggerating as I've never had to do an emergency stop from 60 mph in a coach but the train did pull up very quickly.


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edwin_m

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Brakes on many modern units are adjusted to give a greater deceleration in the emergency setting, typically 12% of gravity rather than 9% for full service brake. This is about half what trams achieve with magnetic brakes and about a quarter of the deceleration in a car doing an emergency stop.
 

Taunton

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Know your history. Magnetic brakes have been around for a long time, being used for straightforward stops, not just for "emergencies". The old London tramways, finally abandoned in 1952, had them on their old tramcars, and would use them at stops along the road. The electro-magnets hung between the wheels on the bogie. Here's one from a tram built in the USA in 1948.

https://www.google.co.uk/search?q=t...ei=V0KFV8mmEom0aYrvnagJ#imgrc=xPg60YJDlSXoTM:
 

Dr Hoo

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Remember that kinetic energy increases with the square of the velocity. A 'loose' human being moving in a train at 125mph would not slow down anywhere near as fast as a coach body hypothetically 'gripping' the track with magnetic brakes or whatever.
Hold very tight, please!
 

AndrewE

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Probably better to invest more in understanding and preventing the "soft" (human) causes of such accidents than building in expensive energy-consuming technology that might not even work when it was needed.

How much would it cost to equip and maintain a whole fleet, compared with keeping staff up-to-date, and feeling valued and unstressed?
 

G136GREYHOUND

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No, it's a daft idea, that wouldn't work, improve existing brakes, improve driver fatigue etc by all means
 

Scott M

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I believe Tyne and Wear metro have magnetic emergency brakes - pretty much the same as what Taunton posted, and from doing a brake test on those from only 80 km/hr they are pretty darn powerful.
 

edwin_m

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Remember that kinetic energy increases with the square of the velocity. A 'loose' human being moving in a train at 125mph would not slow down anywhere near as fast as a coach body hypothetically 'gripping' the track with magnetic brakes or whatever.
Hold very tight, please!

The important things for passenger comfort are the rate of deceleration and the rate at which the deceleration builds up. Neither of these depends on speed, as long as the brakes are able to deal with the amount of heat they generate (which is speed-dependent).
 

broadgage

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Brakes of the current design can not be much improved. Applying a greater force to the wheels would simply result in them sliding on the track, as already happens under some conditions.

Magnetic track brakes are a possibility, but have found little favour for main line stock.

A much quicker stop would also be more dangerous to passengers who could be thrown about and even killed if unlucky.

Also, callous though this sounds, I consider that the lives of the train driver and the paying passengers are worth more than those of a trespasser or suicide.
At present a train driver would apply emergency braking on seeing a trespasser or potential suicide. Depending on speeds and distances, the train may or may not stop in time.
The risks to the driver and passengers are minimal, the risk to the trespasser is significant. But remember that the trespasser CHOSE TO TRESPASS and must accept the perhaps fatal consequences.

Now consider a train with greatly improved brakes as has been proposed. On seeing the trespasser, the driver would apply the much improved brake and thereby risk serious injury or even death to any unlucky passengers.
The trespasser or potential suicide would likely survive to try again.

Is it worth risking the lives of innocent customers, in order to protect the lives of those who are knowingly risking their own lives by deliberate action or by wanton careless use of crossings.

Accidents involving a train colliding with another train at significant speed are now extremely rare. In general such an accident usually requires a most serious and very rare lapse by the driver, such as passing a signal at danger, AND AT THE SAME TIME a failure of TPWS or other systems that are installed to protect against such mistakes.
 

Deepgreen

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Know your history. Magnetic brakes have been around for a long time, being used for straightforward stops, not just for "emergencies". The old London tramways, finally abandoned in 1952, had them on their old tramcars, and would use them at stops along the road. The electro-magnets hung between the wheels on the bogie. Here's one from a tram built in the USA in 1948.

https://www.google.co.uk/search?q=t...ei=V0KFV8mmEom0aYrvnagJ#imgrc=xPg60YJDlSXoTM:

Indeed, but the OP was referring to extending the concept to main line railways, I believe.
 

SpacePhoenix

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I believe Tyne and Wear metro have magnetic emergency brakes - pretty much the same as what Taunton posted, and from doing a brake test on those from only 80 km/hr they are pretty darn powerful.

Are they Telmar or some sort of variant of Telmar?
 

furnessvale

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Are they Telmar or some sort of variant of Telmar?

I don't think so. I believe Telmar(spelling?) is an electric brake for road vehicles similar to rheostatic brakes on rail vehicles. In which case the road/tyre interface is still the weak point in the link just as the wheel/rail interface is for rail with its ability to slip.

The sort of electric brakes being discussed here rely on using the rail itself, bypassing the potential slip of rail to wheel.
 

kieron

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There are slides from an ATOC presentation on this here (as well as a number on other subjects).

It describes their use on Tyne & Wear as being to apply them when needed, and to release them again once the train has slowed down enough to be able to stop without them. The ones used there are not designed to reduce braking force as the train slows, so stopping with track brakes on could be unpleasant for anyone standing on board.

It talks about the benefits in terms of increasing capacity rather than reducing incidents. It could be expensive to implement, but so are many of the other things the industry has done to increase capacity.
 

Taunton

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The Telma Electric Retarder for road coaches became popular in the 1970s when road vehicle brakes were notably poor compared to nowadays. It uses what is essentially an electric motor in reverse mounted around the transmission shaft, controlled by the driver by a separate lever. It's best use is for controlling vehicle speed downhill, avoiding brake fade in conventional vehicle brakes. A number of previous serious coach accidents on steep hills caused it to come into prominence, but now vehicle braking performance is much better.

The detail of the T&W vehicles shows they are just used where normal tread brakes are inadequate, such as in autumn low adhesion. This is different from the old tramcar magnetic brakes which were used for service stops at each stop.

Old trams in London had no auxiliary power systems on the vehicles, such as hydraulics or air for brakes (nor even a 12 volt low voltage supply), and so everything had to be done, if at all, at the full 550v line voltage. The controller had typically about 8 forward power notches, four series and then four parallel. Back past the 0 point in the opposite direction were braking notches (rheostatic brake), maybe two, which operated by essentially reversing the motor connections to make them generators, producing a current instead of using it, which was then dissipated in the normal power resistances. Beyond this, further notches caused the magnetic brake (if fitted) to come into play as well, clamping the magnetic shoes to the rail.

The electric rheostatic brake falls off as speed does, so for a final stop another brake is required. The mag brake has the opposite characteristic, and is more effective at slower speeds, so the two together are complementary. Note that none of this has used conventional brake shoes on the wheels. All trams had these as well, applied by a large wheel or handle.

London went extensively for the magnetic brake, Glasgow was more modern and installed air compressors and used air brakes instead on brake shoes, even fitting these to older vehicles. Manchester apparently had neither, and until the end of trams there in 1949 pulled up at each stop by the driver hauling on the handbrake.

Electric brakes are fine but depend on the line voltage being available, so if descending a hill and the power supply fails (or, for trams, the trolley pole comes off), the brake is unavailable, and therefore you do need full braking ability by another means.
 
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suzanneparis

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Thank you for the many replies.

I was discussing a situation in which a head on collision may occur.

I wasn't discussing the practicalities of various braking systems though nobody mentioned my idea of 'gripping' the track.

When it comes to injuries is there not a trade off between certain death for a number of passengers or serious injury to some passengers due to severe braking?

In the particular case of a head on collision there is the added energy of the other train to deal with. Would it be good or bad to have better brakes to avoid such a collision in the first place? Presumably its a matter of physics and biology?
 

najaB

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I wasn't discussing the practicalities of various braking systems though nobody mentioned my idea of 'gripping' the track.
Gripping the track wouldn't be very effective - first off the brake 'shoes' would likely be contaminated due to being in close proximity to the track all the time with the dust, grease (and worse) and secondly unless it is plain, continuous welded rail there are protuberances of various kinds in the way (e.g. fishplates on jointed track, points, etc.) which would likely break the shoes off anyway.
 

Taunton

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Physically gripping the rail sides is not possible due to the presence of various items right up to rail surface level, such as level crossing road surfaces, check rails, point blades, boarded foot crossings, etc. Even if a means could be devised to keep the grip shoes normally clear of these but able to exert sufficient sideways force when activated, one of these would do considerable damage - in fact if they were gripping hard enough to give serious deceleration when hitting a level crossing or points, a derailment would be likely. This wasn't an issue with tramcar mag brakes which push downwards on the running surface of the rail.

I do have a concern about passengers being thrown about nowadays, more from the current desire to reduce seating and make more passengers stand. Standing passengers are not allowed on coaches on motorways but we somehow accept them on trains at comparable speeds.
 
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Philip Phlopp

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Physically gripping the rail sides is not possible due to the presence of various items right up to rail surface level, such as level crossing road surfaces, check rails, point blades, boarded foot crossings, etc. Even if a means could be devised to keep the grip shoes normally clear of these but able to exert sufficient sideways force when activated, one of these would do considerable damage - in fact if they were gripping hard enough to give serious deceleration when hitting a level crossing or points, a derailment would be likely. This wasn't an issue with tramcar mag brakes which push downwards on the running surface of the rail.

I do have a concern about passengers being thrown about nowadays, more from the current desire to reduce seating and make more passengers stand. Standing passengers are not allowed on coaches on motorways but we somehow accept them on trains at comparable speeds.

Axle counters are the killer for gripping the sides of the rail with an emergency brake.

The focus, as ever, should be on preventing trains from colliding or hitting obstacles (idiot farmers in their idiot tractors) using crossings.
 
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