Track and train protection systems - can someone explain the types and differences for the layman (non driver)

For those of us that don't live and breathe Pandrol clips
Can someone explain the systems of protection where and when they are used from
detonators, Short circuit bar, 15/200/20 advice, DRA ,AWS, TPWS, TPWS+ and any others

These terms confuse me . Why isn't there just one system in use on all lines that just works like a single line token. There must surely have been enough time since Railtrack / Network rail took over.

mrg9999 said:

Can someone explain the systems of protection where and when they are used from
detonators, Short circuit bar, 15/200/20 advice, DRA ,AWS, TPWS, TPWS+ and any others

Click to expand...

TPWS is well described by @Annetts key in this post and on Wikipedia. As is AWS.

mrg9999 said:

These terms confuse me . Why isn't there just one system in use on all lines that just works like a single line token. There must surely have been enough time since Railtrack / Network rail took over.

Click to expand...

Railway signalling has evolved since Victorian times, as emerging technology has made more and more things possible in dealing with ever-evolving hazards and perception of risk. The length of time it takes to roll out any system nationwide and the need to have backwards compatibility makes it inevitable there will be more than one system in use at any one time. (Similar considerations apply to computers and telecoms, hence why analogue telephones and the LW transmissions from Droitwich are only just being switched off [the latter also provides signals to off-peak electricity meters])

This article gives a reasonable overview of the history of all this.

I think you’re listing too many things as ‘protection systems’. For example, a short circuit bar is a means of forcing switch off of the third rail. It’s something that traincrew would use only in a third rail area after an incident. (But maybe you were thinking of track circuit clips?) Detonators are also a post incident procedure. 15/200/20 is I think a shorthand for a professional driving policy? DRA is a driver reminder appliance, it‘s procedural, not quite train protection.

So in my opinion all you really need to consider are AWS and TPWS. TPWS+ extends TPWS to greater coverage of signals.

mrg9999 said:

For those of us that don't live and breathe Pandrol clips
Can someone explain the systems of protection where and when they are used from
detonators, Short circuit bar, 15/200/20 advice, DRA ,AWS, TPWS, TPWS+ and any others

These terms confuse me . Why isn't there just one system in use on all lines that just works like a single line token. There must surely have been enough time since Railtrack / Network rail took over.

Click to expand...

Why is there not a single system? Because they were all developed at different times to "solve" or mitigate different problems. Plus, in many cases, when they were developed for use there were limits with the technology or with the amount of funding available.

Detonators, also known as railway fog signals are small explosive devices contained in a small metal case. It's extremely hard to accidentally set one off. But when placed to the top of a rail, a train will cause one to detonate (he certainly the name). The resulting very loud bang can be heard in the cab of a train, thus alerting the driver.

They are used by railway staff in certain circumstances. Although used less than in the past.

Normally most used these days as part of the protection arrangements for engineering occupations of the line (also called T3 blocks). But are also carried by lookouts (staff protection) and on board trains, for use in an emergency. Mechanical signal boxes may also still keep a supply. Handsignallers also used to carry them but I don't know about now.

I don't know about short circuit bar.

Lookouts and trains also carry emergency track circuit operating clips. They are two metal clips connected by a cable. The clips are applied to the two rails of a track circuited line to cause the track circuit to show occupied (as if a train was present) so that the relevant signal or signals are held at red. Used for emergency protection.

I don't know about 15/200/20 advice.

I explained AWS in this post

TPWS has been explained already somewhere on these forums. If/when I find the post, I'll update this post with a link. Meanwhile, have a read of the Wikipedia article here.

TPWS+ is an extension of normal TPWS. It adds an additional OSS (over speed system) further away (on approach to) the signal that is protecting points or a junction in order to extend the system to deal with trains travelling above 75mph up to 100mph.

Pandrol clips fasten the rail to the sleepers. The Pandrol UK Track Fastenings Guide is here: https://www.pandrol.com/wp-content/uploads/2021/08/V16025_Pandrol_User_Guide_Update_2021_WEB.pdf.

I can explain train protection on the Southern Region as it was forty years ago. Some things don't change over the years, although their application to todays railway certainly has. So bear in mind that then, trains always had a two crew (guard and driver), slam doors and the only communication with the outside world was usually via a signal post telephone.
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Train protection comes in to play when a train comes to an unplanned halt. This could be for many reasons e.g. passenger pulls the emergency cord, train develops a fault, driver becomes incapacitated etc. If the train has a Loudaphone, talk to the driver to find out if he knows why the train has stopped. If no Loudaphone, go up to the front to find out. If he has no explanation, check that there is nothing fouling and adjacent running line (no open doors, no obvious derailment). If a line is fouled, track circuit clips should be applied. These connect the two running rails and mimic the presence of a train. This causes the rear signal to show a danger aspect, and should also be visible to the signaller.

If the train requires assistance, the has to be protected by laying detonators. Usually the Guard protects the rear of the train and the Driver protects the front. This achieved by placing one detonator 100 yards away from the train, one at 200 yards, and three detonators six feet apart a quarter of a mile away. At that time there was a long list of items that Guards had to carry, and that included 'not less than 12 detonators'. They were also stored in driving cabs.

Short circuiting bars create a short circuit between the conductor rail and one of the running rails. In the normal course of events, they should only used when Electrical Control advise it, as they only reduce the voltage of the conductor rail over a short distance. not a true short circuit. However in an emergency (person in contact with the conductor rail) they can be applied by traincrew, but additional equipment is required (shoe paddle and rubber gauntlets) and everything including your clothing must be dry before applying the short circuiting bar.

Track circuit clips, short circuiting bars, hook switch poles, shoe paddles, gauntlets and detonators were carried in driving cabs. As mentioned above, Guards had their own supply of detonators for use in situations where there was no access to a driving cab.