It's Electric! - The Westinghouse Brake and Signal Style L Frame

Every so often I mention the Westinghouse Brake and Saxby Signal Company which was the result of the British Commonwealth's Westinghouse Brake Company purchasing the then dominant UK railway signaling supplier Saxby and Farmer in 1901. For those of you who are unaware, George Westinghouse's claim to fame was the invention of the automatic railroad air brake and he set up corporate entities in both the US and overseas to market his produce. In an early example of corporate synergy, Westinghouse also became involved with railway signaling, either directly producing signaling hardware or owning a signaling subsidiary in many markets. Because there is little sense in reinventing the wheel, the Westinghouse corporate empire would cross-license signaling technology between its various arms. This is how US&S became the supplier of the Improved Saxby and Farmer type mechanical lever frame in the United States and how WB&SS Co would come to sell a power interlocking machine awfully similar to what would become the Model 14 family sold by US&S.

Balham Signalbox Style L Power Frame

As railway signaling moved from purely mechanical to incorporate automatic blocks, electric signals and power operated point machines, interlocking machines effectively became hybrids with both mechanical and electric locking. 19th century mechanical methods would continue to provide the route locking, while magnets and solenoids would lock the levers electrically based on track or switch position circuits. 

Electric locks on a traditional "armstrong" type lever frame.

Since safety critical railway signaling relays were quite expensive, signaling suppliers had an incentive to carry out as much logic as possible in the mechanical layer. Therefore even "power" interlocking machines like the GRS pistol grip style or US&S crank lever style still made use of miniaturized mechanical locking grids. 

Westinghouse owned Union Switch ad Signal had already been the North American licensee of the Improved Saxby and Farmer mechanical locking system and has been using it in its crank style power interlocking machines since the 1890's. In 1901 the newly minted Westinghouse Brake and Saxby Signal Company was suddenly in a position to employ US&S's innovations in Commonwealth countries and came out with its Styles A and B interlocking machines, localized for British signaling tastes.

WB&SS Co Miniature Lever Frame in British Service

Like the crank (ie "Model 14") style interlocking machines in North America, the Westinghouse power frames had three distinct logical components inside the box. First, a mechanical locking grid of the S&F type handling route locking. Second, locking magnets that would lock lever travel based on the state of the electric relay logic. Third, electric contact spindles that would make or brake electric circuits depending on the position of the lever. 

Style K frame with mechanical locking grid.

Style K frame contact spindles.

A route conflict would result in a hard lock as steel bits in the locking grid would physically block movement. An electric problem like points out of correspondence or an occupied track circuit would create a soft lock as the lever was stopped by magnetic latches interacting with a rocker arm on the lever spindle. Anyone who has visited HARRIS tower and its functional Model 14 knows the difference in feel between hard and soft.

Magnetic "soft" locks on a Model 14 machine.

All of this was fine until 1929 when the 23 ton weight of 311 lever London Bridge Style K interlocking machine made Westinghouse Brake and Signal question the sustainability of the technology. Unlike North American pattern machines, the British pattern was less lever efficient, needing more physical levers to carry out the same functions. This not only created a weight problem, but also a size problem as the locking grid dimensions grew literally by the square of the lever count. While American railroads had the space to build beefy towers with wide dimensions, the "early adopter" British railways had harder clearance constraints, especially in major cities where large power frames were most likely to be built. For example the aforementioned London Bridge signal box had to orient its locking bed vertically, making the tower an extra floor taller.

 

London Bridge Signalbox

The solution to this was the Style L frame. Externally the Style L looks exactly the same as the Style K, however internally it is quite different with the mechanical locking grid being completely done away with and replaced by electric locking. the Style L existed as yet another step between the purely mechanical interlockings of the 19th century and the all-relay plants that would ascend in the 1950's. However for anyone wondering why an electrically interlocked plant would even bother with clunky miniature levers, there are some advantages. First it maintains a familiar UI and reuses many of the components that were already in production. Second, it still reduces the number of high cost safety critical railroad relays. The latter is not entirely obvious, but an electro-magnet that unlock a contact spindle that a human then turns, is performing many of the same functions as a vital relay without the same need for precision manufacturing. The website covering Westinghouse power frames has both patent and part information so I'll leave digging down into the fine details of how this electric locking was carried out as an exercise to the reader. 

Style L parts

Style L restored

Style L relay locking logic

The Style L completely displaced the mechanically locked style B and K frames on the main line UK rail network with a burst of new deliveries being made to the British Rail Southern Region between 1948 and 1953. Additional frames were delivered to South Africa up until 1960 with a final BR frame delivered in 1962. An interesting ramification of the Style L all-electric logic was a far greater degree of adaptability than those with mechanical locking. In North America, all railroads (except naturally the PRR) had to hire US&S to perform major modifications to the mechanical locking grid. However the Style L electric locking could be modified without the need for specialized tools and British Rail was able to manufacture quite a few "new" Style L plants using left over components or even spare frames obtained for redundancy purposes during World War 2. Even after retirement from main line service, both heritage and miniature railways have been able to adapt surplus Style L equipment for their own track layouts.

 

The final act of the Westinghouse power frame would play out on London Transport in the form of the mechanically locked Style N and Style V frames as their modest lever counts and subterranean placement didn't trigger the same sort of weight issues seen on the main line railroads. In fact, the last Style V frame, think a Model 14 automated by pneumatic actuators) was installed on LT in 1993! (Which goes to show just how wedded the British were to mechanical technology.) With the closure of Wellington A Signalbox earlier in 2025 and Liverpool Lime St in 2018, the last active Style L outside of preservation might be the signalbox at Maidstone East, which was fittingly the last new built Style L delivered in 1962.

A Tale of Two British Railway Signaling Public Information Films

 The UK is well known for a certain style of public information film that were professionally produced up through the 1980's. A couple go into great detail into the ins and outs of Railway Signaling and served as both a way to increase the public standing of the nationalized railways network in a time of both austerity and modernization and as a recruiting tool to bring new workers with new skills into said modernizing rail industry. 

The first film, entitled Electrical Engineering on the Railway and produced in 1962, falls more on the recruiting side of things as relay based "electric" signaling replaced largely mechanical manual block signaling on the busiest unresignaled main lines of British Rail. While this may been a bit odd as North American signaling has largely discarded purely mechanical signaling by the 1920's, Britain might get a bit of a pass given the toll a pair of World Wars took on its railways and economy.  Point of note include:

• A general lack of safety practices including, but not limited to protective clothing and burn pits for demolished signalboxes.
• The appearance of pneumatic point machines and North American supplied GRA Model 5A electric point machines.
• Rather flimsily looking track circuit bonding wires.
• The continued construction of brand new mechanical lever type interlocking frames.
• Some components of interlocking hardware being hand forged in house.
• A general use of North American pattern glass case plug-in and shelf type relays.
  

The second film, entitled Points and Aspects, was made in 1974 and shows the leap in British signaling from what one might call an updated basic CTC plan to something that was making far more use of computer and telecom technology to enable the so called wire area "Power Box" era of British signaling with as much automation as 1970's technology could muster..  This film is definitely trying to sell the public on British Rail not being a basket case and is worthy of their continued support and patience.  As a result an emphasis is given to the higher tech elements.

What is especially fascinating is that these two videos appear to span the moment when  the UK went from a very North American leaning approach to signaling technology, to a more European approach. Despite very different operating practices, North America and the UK had very closely aligned signaling supply companies with both GRS and US&S licensing UK technology and then supplying their own products back through local subsidiaries like Westinghouse. In the 1970's we are seeing the end of the glass case relays and Model 5 and M3 point machine that stared in the 1962 film.

1960's British Branch Line Cab Ride Films

So while this is a rail signaling blog and not a railfan video blog, sometime I like to highlight sets of videos that really show off the signaling.  Recently YouTube suggested a number of grainy 8 or 16mm film film compilations taken out the front of old school British DMU's running on long since defunct branch lines.

The videos were posted by the appropriately British sounding Alen Snowdon and were narrated by his wife.  Due to the limitations of old school home film recording, the clips are all about 3-5 seconds long and show only a fraction of the route.  However this fraction contains a large proportion of the signalboxes and signaling apparatus that the train passes.  It's sort of like one of those low frame rate fast motion videos, only the frames are a few seconds of every passing semaphore signals.



Not all of the videos are cab rides or even rail related, but the ones that are, are a wonderfun time capsule showing the anachronistic state of the British rail network in the 1960's.  Thanks to two World Wars even the main lines were stuck in he Victorian era, with very little power signaling and steam hauled trains galore.  Just before the infamous Beeching Cuts, the branch line infrastructure is absolutely decrepit, sort of like how the Amtrak Harrisburg Line and Conrail in general looked in the 1970's and 80's. 



Also worth noting is the astonishing level of employees needing to keep these old branch lines in operation with both signalmen and station agents working every 1-3 miles along the line.  It is interesting that instead of cuts British Rail didn't simply try massive cost reductions like CTC or even ABS!



There's even a little main line action out of london, although one would never know it due to the state of disrepair. Also note the high quality railfan view despite a full width cab. Anyway, enjoy the videos, they aren't hours long and the archive isn't intimidating.

Liverpool Lime Street Signalbox Closed

One of the last two active Westinghouse Brake and Saxby Signal Company power frames on British Rail was taken out of service on July 13th and it was quite an impressive example, controlling the 13 track stub terminal in Liverpool, England since 1948.  This matters because the WB&S Co Style L power frame installed in Liverpool Lime Street is pretty much a US&S Model 14 just with the levers rotated 90 degrees to moved in the proper British fashion.  Also the all brick structure with a bay window follows the pattern of high quality North American towers as seen on the Pennsylvania Railroad or New York Central.

With 86 active levers and a plant that had pretty much remained untouched since the signalbox was constructed after The War, this is a huge loss for living signaling history, although a number of these frames survive in various preserved forms.



The machine was shut down track by track instead of a simultaneous cutover.  This resulted in the unfontunate side effect of the model board being completely painted over aside from the last two active tracks along the bottom :-( All of this can actually be scene along with general tidbits about the Signalbox's history and future use in this video produced by Network Rail.




Unlike many other British towers Lime St is a listed building and should be preserved along with the rest of the station. Also make sure you check out the The Westinghouse Brake & Signal Company Ltd. Miniature power lever frame website for more information on this cross pond cousin.

Swindon Power Signalbox Restoration

Hopefully most of you are familiar with the excellent job the crew at HARRIS tower has done reactivating its US&S Model 14 interlocking machine with the help of a lot of PLC's and Train Dispatcher 3.  Well over in the UK a project is afoot  to do the same thing to the old NX panel from the Swindon Power Signal Box.  The "PSB's" were a generation of British area signaling control centers that replaced the most hard pressed mechanical tower in the 1960's and 70's.  They used a lot of relay logic to implement push button N-X operation and many eventually came to feature integrated train description.  A tour of Swindon PSB can be seen below.



Swindon, like many other PSB's, are being removed from service because many of the telecon grade relays that drive the user interface and other ancillary logic are becoming nearly impossible to maintain.  Here below is a video showing the "domino" style panel board being re-assembled after it arrived at its preservation site.



Here is a brief demo of the old panel UI hooked up to some modern electronics.  And yes that is indeed the Danny Scroggins who is so well known for his comprehensive documentation of vintage British signaling and signalboxes.



Of course there is an entire Youtube Channel devoted to the project, with videos like this one showing the progress of the custom PLC components.



In fact the panel has its own preservation society and as of now they are projecting an grand opening date of June, 2018, plenty of time to score that cheap transatlantic airfare.

British Power Signal Box Video Tours

On a British signaling forum I frequent, a signaler known as Ian Ives uploaded a number of VHS video tours he made of some London area British Power Signal Boxes (also called Panel Signal Box or PSB) back in the 1990's.  For those of you who don't know, a PSB is roughly equivalent to the type of interlocking tower that was largely passed over in North America in the evolution from single interlocking towers to dispatch offices. They are basically what the NYC Subway calls Master Towers.

Popular in the UK between the 1960's and the 1980's, they replaced most of the electro-mechanical interlocking towers in busy urban areas as well as scores of pure mechanical towers.  PBS's contained large NX style model boards with light green tiles.  Their most high tech feature was automatic train description using small LED or CRT display boxes, which in the 1960's was quite a feat indeed.   While well documented pictorially, there are relatively few video records of how these panels were worked so check out these great resources.

If you like these, make sure you visit and/or subscribe to Ian's channel here.  If you would like an official tutorial on how these panels worked, you can find it here.