Token block token exchange question

[zwk500]

I've long been surprised that Centralised Traffic Control (CTC) never took off on UK single lines. Developed in the USA well over 100 years ago, it was extensively installed on Colonial rail systems in Africa. It just uses the same lineside wire pair as block signalling does, and where in Britain a signalbox controlling say 100 miles of line is a major structure, the equivalent unit for CTC is often just a console for one operator in a handy back room at a station.

How significantly does CTC differ from TCB with a PSB or IECC?

 

[Taunton]

Elements of single line working have long fascinated the general public when passengers. I have enjoyed the disbelief when they say there is "only one token" for the section, and I correct them and say it's normally set up with 20, 10 at either end.

Two old ladies at the front of a heritage line dmu obviously recollected past journeys on the main network as the key token was handed over. "Look, I remember that, the other man comes and gives our driver a lollipop".

But best was Papa and small son with faces at the front window as a traditional wooden staff was passed over.

"What's that dad?".
"That's so there's only one train on the line".
"How does it do that dad?".
"Well, if we see another train coming the other way, our driver can stop, go over to the other driver, and hit him over the head with it ...".

 

[MarkyT]

I've long been surprised that Centralised Traffic Control (CTC) never took off on UK single lines. Developed in the USA well over 100 years ago, it was extensively installed on Colonial rail systems in Africa. It just uses the same lineside wire pair as block signalling does, and where in Britain a signalbox controlling say 100 miles of line is a major structure, the equivalent unit for CTC is often just a console for one operator in a handy back room at a station.

It didn't catch on in UK before WW2, but inspired post-war panel schemes, though not initially covering the large areas that US implementations did. In the USA, the system had remote relay interlockings at junctions in the field and extensive track circuiting between so would also run into high cost issues on very marginal routes. Early electromechanical CTC telemetry was a bit clunky and slow, limited by the technology of the 1920s. By the time the UK was widely deploying remotely controlled relay interlocking in the 60s and 70s, more capable solid-state TDM remote control and monitoring systems were available that could command and supervise large remote interlockings over two wire pairs. The track circuit was invented in the USA around the turn of the 20th century, and commercially oriented railroads there eagerly and quickly exploited it to extend control areas. Though at first the system was considered expensive it was often worth it on busy lines where CTC helped grow traffic and improve performance.

How significantly does CTC differ from TCB with a PSB or IECC?

Essentially the same. The panels are a bit like early IFS (individual function switch) panels in UK. You throw all the points individually for the required route before separately clearing the signal. You have to press a code button to send each request to the interlocking.

Clunky and slow:

 

[Annetts key]

OK, so let's invert the question - if the entire system is reliant on drivers obeying signals then why did we ever need tokens on single lines?

The original purpose of most signalling equipment from a system safety point of view was to try to reduce the possibility of a signaller making a fatal error that may result in deaths or injures. Although some changes have been made to also try to mitigate errors made by drivers (ATC, AWS, ATP, TPWS, DSD, DRA, ETCS/ERTMS and so on) most of these are relatively recent technologies.

The purpose of a single line token is to try to prevent the possibility of signallers letting two trains on to the same section of (single) line. Especially two trains proceeding towards one another at speed.

As MarkyT says, the multiple track circuits, the cables and relay and electrical interlocking equipment for/on long sections were expensive. A single train staff in comparison was cheap and effective, one train staff means only one train per section. A driver, when they have possession of the train staff knows that they, and only they, have authorisation to enter the single line section. And as there was only one train staff, only one signaller could hand it to a driver. It was now not possible for a head on collision to occur if the rules were followed.

However, a single train staff does put limits on operational flexibility. With some methods of working on a single line, this was relaxed slightly to allow one train to follow another in the same direction. The driver of the "first" train was only shown the token or train staff. The driver of the following train was given the train staff, but only permitted to proceed after either conformation that the first train had left the section (arrived at the next block post). Or a suitable time interval had elapsed. This system however, still allowed simple human errors or the break down of trains to result in (rear end) collisions.

The token systems with instruments that contained them and electric locks to only allow one token to be extracted at a time, but which now allowed unequal flows of traffic through a single line section both greatly increased system safety and allowed more operational flexibility.

Token systems only needed one pair of telegraph wires. A token instrument at each end. Maybe an intermediate instrument if there was a ground frame (G.F.) on the single line between block posts (signal boxes). And sets of batteries to power the token instruments. The length of the section does not affect the cost (within reason). Even twenty to twenty-five years ago, token systems for lines where speed and capacity were not important factors, were seen as cost effective.

And the system was considered foolproof until the collision at Abermule in 1921. After that, further improvements were made.

The token instrument system is effectively the equivalent to the absolute block instrument system used on pairs of unidirectional lines.

 

[MarkyT]

A more recent video of BK tower CTC showing its coding equipment:

 

[MadMac]

BR was working on a CTC-style system for York-Beverley prior to the line being proposed for closure under Beeching.

 

[CC 72100]

As an aside. I always thought St Bees made for an interesting debate regarding DRA. The signal can be cleared but in itself doesn't form your authority to leave until the signaller completes their long walk over the bridge to the cab.

At a (different) location I sign, the technology is similar so the starting signal can be cleared once the Token is removed but before the Signaller has delivered to the Token to the driver.

I personally set the DRA until I have the Token; as far as I am concerned, I need both the signal AND Token to be able to proceed, and so the DRA stays set even if the Signal is cleared until I also have the Token in my hand. If you take the view that the DRA is reset with authority of movement, you don't have that authority until you have the Token too.

 

[MarkyT]

BR was working on a CTC-style system for York-Beverley prior to the line being proposed for closure under Beeching.

I read about that. A contract had been signed with Westinghouse, some materials delivered and prep work started. I doubt it would have differed much from other 60s panel schemes in technology, probably using electronic TDM telemetry to remote control relay interlockings, a technique recently pioneered in 1959.

 

[MadMac]

I read about that. A contract had been signed with Westinghouse, some materials delivered and prep work started. I doubt it would have differed much from other 60s panel schemes in technology, probably using electronic TDM telemetry to remote control relay interlockings, a technique recently pioneered in 1959.

Westinghouse’s ‘F1’ TDM system was well-established and proven by that point so that would have been the “platform” used.

 

[Lucy1501]

I suspect that there is a machine in Bransty box, even if a token is rarely removed from it: possibly only for testing or the odd engineers train.

Bransty has never had a token machine in the box, the only one is on the platform. It was TCB with acceptance lever up until the 1990s, when Corkickle No.1 and No.2 both closed, at which point the present method of working was installed.

There is instead a rather unique instrument, I believe the only other one being at Melton Mowbray, which can be used to remotely operate the token machines and send bell signals. There's a photo here: https://www.flickr.com/photos/jjm2009/52601148703/

 

[Ashley Hill]

There is instead a rather unique instrument, I believe the only other one being at Melton Mowbray, which can be used to remotely operate the token machines and send bell signals. There's a photo here: https

That looks like it’s made from old parts found in the linemans cabin.Second hand galvanometer and indicator. Does the job though .

 

[Rescars]

.

Token systems only needed one pair of telegraph wires. A token instrument at each end. Maybe an intermediate instrument if there was a ground frame (G.F.) on the single line between block posts (signal boxes). And sets of batteries to power the token instruments.

Your Username suggests there could be no-one better qualified to comment on arrangements for unlocking a mid-section ground frame!

 

[Annetts key]

Your Username suggests there could be no-one better qualified to comment on arrangements for unlocking a mid-section ground frame!

Aye. The image is a Western Annetts Key Release instrument that once was common across Western. The key was used to unlock a ground frame (G.F.) from a signal box or P.S.B.

I worked on these (instruments and ground frames) many, many times during my working life.

Well, for token sections, the practice that I saw on Western at such ground frames was as follows. A token hut was provided next to it. The hut was opened with a B.R. No.1 key. Inside there was a token instrument and a telephone to the relevant signal box. The G.F. was designed such that the token when placed in the mechanical lock, could be turned. This would release the F.P.L. lever. When the F.P.L. was unbolted, this released the point lever.

A train therefore could be stabled clear of the single line. Or it may be a branch line to private sidings.

 

[Falcon1200]

Pilot working at first if trains need to run. As others have said, losing a token is considered a very serious matter. Tokens are not small, so there is no excuse for misplacing one. Similarly staff should take good care of them.

They certainly should. However there is (just) one incident I recall when a token went missing, not because it had been dropped or mislaid, but was stolen after being left in a cab while the Driver took a break!

 

[Harpo]

There have always been the ops irregularity with tokens. Train without token and train with additional token both had acronyms.

 

[MarkyT]

Aye. The image is a Western Annetts Key Release instrument that once was common across Western. The key was used to unlock a ground frame (G.F.) from a signal box or P.S.B.

I recall similar instruments used for point crank handle release. They had a different style of key that wasn't compatible with standard Annetts instruments. Like a GF release, the signaller would operate a control on the panel to release the key. Modern schemes don't have this feature. It was fairly pointless (sorry) as the handles were generic for the machine type so if you happened to have one in the van...

I worked on these (instruments and ground frames) many, many times during my working life.

I've got one, with a key, somewhere among the junk in the garage. I don't know where it was from and there are no identifying labels. When I finally finish clearing and selling this house I intend to display it with my permissive block instrument, bell and indicators in my new place.

Well, for token sections, the practice that I saw on Western at such ground frames was as follows. A token hut was provided next to it. The hut was opened with a B.R. No.1 key. Inside there was a token instrument and a telephone to the relevant signal box. The G.F. was designed such that the token when placed in the mechanical lock, could be turned. This would release the F.P.L. lever. When the F.P.L. was unbolted, this released the point lever.

A train therefore could be stabled clear of the single line. Or it may be a branch line to private sidings.

Some in-section ground frames didn't have an intermediate token instrument. They were still mechanically released by the token for shunting, dropping and collecting wagons, but you couldn't lock a complete train with loco inside the sidings to run another one past it.

 

[Taunton]

As well as ground frames, similar arrangements applied for where the pw gang motor trolleys were stored. These were quite common on Western single lines, being stored alongside the line at various points, at right-angles to the track and being manhandled there with a turnplate. The location also had a token machine, for the trolleys of course needed a token when running in the section. There must have been quite some complexity with arranging these, as sometimes the worksite had two trolleys and gangs there, working independently, and sometimes they worked on Sundays when the signalboxes were closed.

 

[MarkyT]

As well as ground frames, similar arrangements applied for where the pw gang motor trolleys were stored. These were quite common on Western single lines, being stored alongside the line at various points, at right-angles to the track and being manhandled there with a turnplate. The location also had a token machine, for the trolleys of course needed a token when running in the section. There must have been quite some complexity with arranging these, as sometimes the worksite had two trolleys and gangs there, working independently, and sometimes they worked on Sundays when the signalboxes were closed.

Likely the signallers would issue a token for the possession after passage of the last regular train before going off duty in the last case. A PW gang member would have to be present to withdraw the token from such an intermediate instrument, then take charge of its safekeeping for the duration of the possession, or sometimes there could be an agreed safe place the signaller could leave such a token for later collection. An intermediate instrument requires a simultaneous release from both signalboxes holding their bell plungers in. Once an engineering possession is taken, there can be multiple rail vehicles and movements within it, controlled by the person in charge of the work. Taking out a token for a possession, whether from one of these special intermediate instruments or from either of the main signalbox instruments at the section's extremities, ensures the system is out of phase and cannot issue another token for a normal movement from either end, even if the next signaller on duty has no idea what is going on when they arrive. Clearly the possession arrangements should have been detailed in a train register entry by the previous signaller granting it, but the track gang actually possessing a token while working is further belt and braces protection for the personnel should there be any confusion. The train register is a logbook listing the times of all the main block events for each train signalled; e.g. Line Clear, Train Entering Section, Train Arrived Complete. Other important occurrences are also recorded such as possessions granted and given up, restrictions to certain items of equipment due to failure or ongoing maintenance activity, tests, handbacks etc. If in doubt, write it down in the register!

 

[Annetts key]

I recall similar instruments used for point crank handle release. They had a different style of key that wasn't compatible with standard Annetts instruments. Like a GF release, the signaller would operate a control on the panel to release the key. Modern schemes don't have this feature. It was fairly pointless (sorry) as the handles were generic for the machine type so if you happened to have one in the van...

Note, the following is my experience on Western. I don't know how this compares to other regions.

For handcrank release instruments, yes, they were similar. The "key" was actually an integral part of the (point) crank handle. These were actually far better quality than the plain point handles that were available.

Under B.R. even in the late 1980s, only some groups of staff were allowed point handles. Many S&T maintenance staff had to use the handles from the handcrank release instruments. Especially if you were at a junction with a point machine type that you did not have a compatible handle for...

When you wanted to work on a set of points, you had to ask the signaller to release the handle. The signaller had an indication that told them if the handle was detected as being in the instrument.

For the 1960s through to 1970s M.A.S. "Panel" P.S.B. schemes on Western (apart from junctions that had been later renewed with clamp locks) every major junction and the vast majority of minor junctions had at least one handcrank release instrument.

For junctions local to the signal box or local to the P.S.B., no instruments were provided. Instead, if you did not have a handle, you had to book one out from the signal box.

Instrument handcrank handles existed for 5A, M3, HW and I think 63 type point machines on the area where I worked.

But these instruments fell out of favour. Whenever any signalling work was carried out that affected a junction, the control circuitry and the instrument(s) were removed. The instruments recovered were raided for spare parts to keep the G.F. version operational.

Sorry, we have drifted off topic...