How Railway Signalling is Replaced: Summer Engineering Works at Nottingham

Every so often, it is decided that a given station should be "resignalled" or "remodelled". This summer, it was Nottingham's turn, and as a result almost no trains ran to or from Nottingham for the six weeks from July 20th to August 25th. This meant buses, and lots of them - leading to inconvenience for thousands of passengers in the height of summer.

In this blog I'm going to try and explain why it was done, and how the railway companies got around it. (This is based in part on my experiences roving round the area over the weekend of Friday 9th-Monday 12th August.)

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First of all, what do I mean by "resignalling"? Well, the signals (which act like traffic lights on the railway) are like any other piece of mechanical equipment: they wear out, and must be replaced. All the signals at Nottingham were installed in 1969, and were thus to be replaced in 2013.

But it's not just the signals themselves that have to renewed, it's all the equipment that goes with it. The points - movable pieces of rail that allow trains to change between tracks, known as a switch or a turnout in North America - also had to be renewed, and so did the track circuits.

A track circuit is a device which measures the flow of current from one rail to another, along a given section of track; when there's no train in that section, (almost) no current will flow, but when a train passes through the section, the axles of the train complete the circuit and current flows. This is the simple yet ubiquitous mechanism by which a train's location is determined across the country.

(Incidentally, a "signalling failure" is unlikely to be a failure of the signal itself, although sometimes a bulb will blow. It is much more likely to be either a track circuit failure, usually when a track circuit registers as "occupied" even when there's no train in it; or a points failure, when a given set of points will fail to move into the correct position, perhaps due to an obstruction.)

Finally - and perhaps most importantly - the equipment that controls the signals, points and track circuits also has to be renewed. The 1969 installation in Trent Power Signal Box (PSB for short), controlling Nottingham and the surrounding area, was state-of-the-art at the time, consisting of a push-button panel at which the signallers stand, controlling the flow of trains. This was to be replaced with a computer system in the new East Midlands Control Centre (EMCC) in Derby, controlled by a keyboard and trackerball.

Behind the panel or computer screen lies the "interlocking", the fundamental system which prevents the signaller from crashing two trains into one another; a signal may only stop showing red if the route ahead is clear, and if the points are set in the correct position. Interlocking has been around since the middle of the 19th century, after a few disastrous consequences of signalmen failing to ensure the points were set correctly.

Trent PSB, in common with most installations at the time, used a complex system of mechanical relays to make up the interlocking: while this has the advantage of being very safe, it's also very cumbersome and takes up several rooms. Instead, the new installation at EMCC has a "solid-state interlocking", where relays are replaced by, essentially, software on the computer, which is just as safe but takes up much less room.

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So what's "remodelling"? Once the signalling for a particular area has been installed, the layout of tracks and signals tends not to change unless there's a reason to (a new platform here, a new depot access route there, a branch line closed down, etc.). But when the signalling does need to be renewed, it is usually a good opportunity to ensure the track layout is appropriate for the services that run; often service patterns have changed dramatically over the 40 or 50 years a signal installation might be used for.

For example, one of the fundamental differences in operation between the railway of 1969 and the railway of 2013 is the decline of locomotives and the rise of multiple units. In 1969, most services had a locomotive at one end, providing all the power for the train, hauling coaches which had no power to move of their own accord. Only a handful of services (outside the busy suburban networks around London) were run by multiple units, trains with engines under the floor distributed along the train.

Quite the opposite is true today: there are very few locomotive operations around, and those that are used (on East Coast and Greater Anglia) tend to be in fixed formations with a "driving van trailer" (DVT) on the other end so that the train can be driven from the opposite end without repositioning the locomotive. (Perhaps the only true locomotive operation left is on the overnight sleeper trains between London and Scotland and London and the Westcountry.)

At Nottingham in particular, though, there was one key part of the layout that was now constraining capacity, namely Mansfield Junction, just to the west of Nottingham where the lines to Mansfield and Sheffield diverge from the mainline towards London. Trains on the north side of the station had to cross over to the south side out of Nottingham station, before crossing back towards the north at Mansfield Junction.

This made sense when, in 1969, most trains at Nottingham were through trains, so few trains would want to get from the north side towards Mansfield; they'd already be on the south side. But these days almost all the services at Nottingham - in fact, everything but the Liverpool-Norwich trains - terminates at Nottingham and goes back in the direction it came from. For this reason, it was decided to rearrange the tracks out to Mansfield Junction so that trains could go in and out on any of the four tracks to the west of the station.

Furthermore, prior to the remodelling there were two "through roads" at Nottingham, between platforms 3 and 4: tracks without a platform, for trains to pass through without stopping. It was decided to split platform 4 in two, extending the eastern half outwards to meet one of the through roads, creating two platforms where once there was one (though the remainder of the old platform would only be accessible to the west).

The end result is a considerably simpler layout at Nottingham station, which should (in theory) be easier to maintain and, importantly, cause less "reactionary delay" - in other words, fewer knock-on effects once one train is delayed. At busy places like Birmingham New Street or Clapham Junction, once one train is running late, that will ripple through many other trains; ensuring a track layout that can be used flexibly is one good way of minimising such delays.

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Getting to that end result, however, meant completely ripping up all the points at the west end of Nottingham station and putting in new ones; with the new points and the new layout came 143 new signals. The track itself - six miles of it! - also needed to be replaced, and coupled with various improvements to the station itself, it was decided that the best way to accomplish the remodelling was to do it in one big hit.

In theory it would have been possible to do most of the work in a large number - perhaps up to a year - of weekend closures. But given the magnitude of the work, it was decided that a six-week blockade - not just on the weekends, but all week as well - was the best course of action. While there may be some who disagree with that, ultimately it's Network Rail's decision.

The high summer period was chosen because there is a notable downturn in commuter traffic - often as much as 20% - during the school holidays, and it would thus disrupt fewer people. However, while commuter traffic falls, seaside traffic rises dramatically - and for Nottingham that means the Lincolnshire resort of Skegness, just over two hours away by train.

To ensure the minimum disruption possible, for four of the six weeks an hourly train service between Nottingham and Skegness was maintained. This was made possible by carefully programming the (less substantial) modifications to the east end of the station, which also permitted a train service between Nottingham and Lincoln to run for the last two weeks of the blockade.

But with the old signals ripped out and the new ones not yet installed, to get even one train into and out of Nottingham station required a much more basic system of ensuring two trains couldn't crash into one another. This is done with "pilotman" working: one man, and one man alone, could give permission for a train to proceed, and a train wasn't allowed into Nottingham without that pilotman on board!

I saw this for myself on Saturday 10th August; while visiting Jonathan in Sheffield, I took a convoluted day trip to Skegness. From Sheffield, I went to Lincoln, and then into Nottingham. All was going well until we were a mile outside Nottingham; we sat for over 15 minutes without explanation, before moving forward half a mile to the next signal and sitting for another 20 minutes. While some of this had been allowed for in the timetable, it wasn't until 15 minutes after we should have arrived in Nottingham that the pilotman finally made it on to our train and we could proceed into the station.

It transpired that one of the earlier trains had been a bit late into Nottingham, and due to industrial action by the RMT union the guard had refused to take the train back out until he'd had his requisite 15-minute break. Eventually, the outward train was cancelled, but that meant the pilotman was in the wrong place - he was in Nottingham station, and all of a sudden needed to be half a mile to the east to get on the next train in!

The reason it took so long to cancel the train was because the controllers didn't really know what was going on; they didn't know which train was where, precisely because there was no signalling system! Only the pilotman did, and once he had talked to the controllers he was able to rectify the situation and make his way out to the next train, whereupon it was able to go in and come out, and then our train was able to go in.

But this lack of information meant that all the usual sources of information were useless: over the last few years, I've got used to using my phone to check the internet to find out when a train is delayed and why. But all that information is powered by the signalling system, and when the signalling system is one man and he's having to run around to get to the right place, there's not much else to do but sit and wait.

In the half an hour I had to change trains in Nottingham, I looked around the station, and boy, was it weird looking round what was basically a giant building site. Just one platform - the old platform 5, now renumbered 6 - was open for trains, the rest being in the process of being rebuilt or having their tracks replaced. The track layout was mostly complete, but the platforms themselves were being resurfaced, and that was clearly left to be finished.

With just one train allowed into Nottingham at a time, it took over 20 minutes to get each train in, unloaded, reloaded, and out again - and with little margin for recovery, my train back out to Skegness was thus also late. Fortunately, although it left 13 minutes late there was a bit of slack in the timetable and after a pleasant run through the countryside we arrived at Skegness just three minutes late.

Notably, though, while the train was not that busy from Nottingham, it got much busier from Grantham. Clearly anyone going to Skegness who hadn't come from Nottingham had been directed to Grantham, with its position on the East Coast Main Line affording links from Peterborough and London as well as the north.

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While pilotman operation permitted a basic service to Skegness and Lincoln, the complete block of the west end of the station necessitated a huge fleet of buses and coaches to ferry passengers between their trains and Nottingham itself. When train services couldn't be provided there were buses to Newark and Grantham for onward trains to Lincoln and Skegness respectively; and throughout the block, the line to Mansfield and Worksop was replaced by buses throughout, the opportunity being taken to replace some track on that line too.

Most importantly, however, five buses every hour ran to and from East Midlands Parkway station. East Midlands Parkway opened in January 2009, ostensibly to serve the nearby East Midlands Airport, but it feels more like it's there to serve Ratcliffe-on-Soar power station, which towers over the station.

With the airport still a shuttle bus away most passengers continued to get a bus from Nottingham or Derby. But with Nottingham closed, people were encouraged to drive to East Midlands Parkway - with a large car-park - where they could get their train, with buses provided to ferry those who needed to get to the city centre.

As a result, East Midlands Parkway came into its own during the blockade, all of a sudden being one of the most-used stations in the Midlands, with trains diverted to mainly use it in place of Nottingham. The London-Nottingham services were mostly curtailed to just run between London and East Midlands Parkway (with some extending to Beeston, just three miles west of Nottingham), and many of the London-Sheffield trains which usually pass through without stopping were re-timetabled to call and provide connections.

In the morning and evening rush hours, there are a few London-Leeds trains which usually run via Nottingham and reverse there before continuing on via Sheffield; these were mostly diverted to use the Erewash Valley, avoiding both Derby and Nottingham but permitting a call at East Midlands Parkway. (It's fairly rare for trains to use the Erewash Valley route in daylight, and I made sure to use one of these trains on the way to Sheffield on the Friday night!)

More importantly, though, the Liverpool-Norwich services were diverted from Nottingham and instead served East Midlands Parkway. This meant they couldn't call at Grantham, but instead ran non-stop between Peterborough and East Midlands Parkway via Melton Mowbray.

These had an added complication, in that the Liverpool-Norwich trains are usually scheduled to be four carriages west of Nottingham but just two carriages east of Nottingham. With Nottingham closed, the dividing and joining of the units had to be done elsewhere. Due to the signalling arrangements, it wasn't possible to join trains at East Midlands Parkway, or at Chesterfield; the obvious solution of joining the units at Sheffield was precluded by the timetable and the lack of capacity there.

Instead, the Liverpool-Norwich trains dropped two of their four carriages in the platform at Chesterfield, and continued via the Erewash Valley to East Midlands Parkway and on to Peterborough and Norwich. The two carriages left in Chesterfield were then taken empty to Derby. Meanwhile the Norwich-Liverpool services, having called at East Midlands Parkway, were sent via Derby to pick up the extra two carriages, before proceeding on to Chesterfield.

To avoid too much confusion, the call at Derby was not advertised, so that passengers would think they were running non-stop between East Midlands Parkway and Chesterfield. However, while on board a Norwich-Liverpool train on the Monday afternoon, I was getting ready to alight at East Midlands Parkway in order to get onto a train that actually was calling at Derby, only to hear an announcement that "passengers for Derby should remain on the train"!

And indeed, while the Derby stop had not been advertised at Peterborough, where I'd boarded the train, at East Midlands Parkway the displays announced that the train was indeed calling at Derby. And so it did; the doors were released on arrival at Derby, before the train was joined to the other two carriages and it proceeded on its merry way to Chesterfield. The displays at Derby, however, simply said the train was "not for passenger use"!

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By far the oddest diversion, though, was that I took on my way back from Skegness that Saturday afternoon. On summer Saturdays, to provide additional capacity, an eight-carriage HST is provided to run between Derby and Skegness via Nottingham. But with Nottingham closed to the west, it would have to take a rather different route to get from Skegness to Derby...

While Nottingham-Skegness trains routinely run via Grantham, the summer HST usually avoids Grantham because trains have to reverse there to run between Nottingham and Skegness. But with Nottingham closed, we proceeded into Grantham, and after waiting our turn proceeded up the East Coast Main Line to Peterborough. This provided the very incongruous sight of an East Midlands Trains HST on what would normally be completely the wrong line!

After waiting fifteen minutes outside Peterborough for a platform (as we were timetabled to do), we reversed at Peterborough before heading via Melton Mowbray and through East Midlands Parkway (oddly without stopping) to Derby.

All in all it took over three and a half hours from Skegness to Derby, and without the call at Nottingham the train was fairly lightly loaded. As usual, though, for an HST run to Skegness, first class was "declassified": in other words, while there were three coaches marked as "first class" and having very much nicer seats, there was no difference in price between those and the cheap seats further back!

So I sat back and enjoyed a relaxing ride through Lincolnshire and the East Midlands. On three occasions, the train went round sharp curves (at Firsby, Allington and Syston); being at one end of the train meant I could see all the way along the train and made the tightness of the curves easily appreciable.

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All in all, then, East Midlands Trains and Network Rail went out of their way to ensure that the disruption from closing Nottingham station was kept to a minimum, with most trains diverted, and buses to replace trains where that wasn't possible.

I was particularly impressed with the pilotman operation for the Skegness and Lincoln trains. While it didn't work all that smoothly on the day I happened to be there, it's impressive that they bothered at all. It would have been much easier to say "sorry, no trains, go get a bus". But to have to bus holidaymakers to Skegness (or at least Grantham) - many of whom had a fair amount of luggage, to say nothing of many people with small children in pushchairs and prams - would have needed an awful lot of buses to make sure people weren't left behind.

Early in September I returned to Nottingham station to see the finished article. The tracks to the west end now permit much higher speeds - allowing trains into and out of the station at up to 50mph - and all the track and signals look new and shiny. The station itself is still in the middle of a much longer rebuilding programme - set to be finished in 2014 - but the really hard work of rearranging the tracks is done.

There was one final reason why a blockade was chosen. To facilitate an extension of the Nottingham Express Transit, the hugely successful tram system opened in 2004, a bridge right over the middle of the station was required. With this having been slid into place during the six-week blockade, the bridge can be kitted out and trams will be running by the end of 2014.

Once a new tram stop has been provided on this bridge, from next year passengers will be able to look forward to a seamless interchange between train and tram, with trams running not just north to Hucknall and Pheonix Park, but south to Clifton, and west to the University of Nottingham, Beeston, and a new park-and-ride side at Toton Lane.

Although effectively closing Nottingham station for six weeks was disruptive, it also paves the way for the next major upgrade of Nottingham's railway: electrification. With the signalling now ready for the electric wires due to be strung up on the Midland Main Line between London and Nottingham by 2019, Nottingham can now look forward to having the kind of transport network the city deserves.