| Part 8: Signalling |
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Before we get going on how to signal the line, it helps to produce a draft timetable to sort out where the ideal passing loop locations are. So here's a basic set-up with the explanation of the reasoning behind it. (This is a timetable designed to show the paths allocated rather than what actually runs in a specific hour. The hours shown are merely for demonstration and to avoid excessive confusion. Anyone trying to use this timetable to catch an actual train will probably miss it; since real timetables are available for free all over the internet, at several high street retailers and all relevant railway stations you should view this as your problem.)
(All the journey times in the WV columns above are uneducated guesses, so the variations between Up and Down journeys to the right would be smoothed out in a practical timetable and Tintern to Cardiff might lose that extra minute somewhere.) This timetable assumes that there will be a few extra stations shoved in on the slow lines between Cardiff and Severn Tunnel Junction with Portskewett station being reinstated for good measure. (The WVR will cost enough without adding in building mainline stations at £4million each, but if someone else builds them WVR trains, always desperate for extra revenue, will happily make the extra stops.) Accordingly trains on Monmouth-bound services are able to be overtaken by trains on the fast lines between Cardiff and Newport. (Cardiff-bound ones are also overtaken between Severn Tunnel Junction and Newport by certain trains.) This overtaking ensures that for journeys to and from Cardiff, Newport and Severn Tunnel Junction the WVR services will rarely show up as the fastest, if ever, and so established operators need not worry about "Orcats raids" (where open-access operators make a profit by extracting revenue from existing trains, not by generating their own). One crossing loop is required on the WVR for this timetable; said crossing loop will go in at Tintern. The proposal is that trains cross here at 40 minutes past the hour, with the Cardiff-bound train being booked to arrive first. The set-up is based around four trains per hour from Cardiff to Chepstow and Chepstow to Cardiff setting off at regular intervals of 15 minutes. The Chepstow to Cardiff service is basically a Metro aiming to obtain as much traffic as possible from several intermediate stations; some of them may well warrant this sort of service and Chepstow is a convenient place to terminate. The schedules of the current trains haven't been touched, although the Cross Country service from Gloucester to Cardiff is required to show some punctual running to avoid being caught behind the Monmouth to Cardiff stopping service, which is due into Chepstow about three minutes after the XC train has gone through. For the purposes of this we run three of the four Chepstow trains up to Tidenham - the ATW one carries on to Lydney, Gloucester and Cheltenham. Without all the extra stops this will allow a convenient five-minute turnaround away from the mainline at an attractive Parkway station and since there is already a crossover at the east end of Chepstow station the only trackwork involved on the mainline will be re-instating Wye Valley Junction. With all the extra stops it becomes a bit of a nightmare since the Tidenham bound train would, on the perfect clockface timetable, run onto the single line beyond Chepstow at exactly the same time as the train from Tidenham comes off it. Therefore we have mucked around with the timings between Chepstow and Tidenham a bit and lost the repetiveness. On the plus side, this leaves a nice bit of timetable padding at Tidenham before returning to Cardiff - which is always handy and is lacking at Chepstow. On the downside, it has a nice bit of timetable padding at Tidenham before returning to Cardiff. Apart from this entailing an expensive train being sat at Tidenham for ages being a rather expensive temporary waiting room, it also means that said train will get in the way of the following train to Monmouth. A stabling siding will be necessary. This can be easily organised by re-instating the station loop and dumping the terminating train there for a few minutes while the Monmouth-bound train goes past. (You can make the 10:27 from Cardiff the Monmouth train and the 10:42 a Tidenham service, but then the Monmouth trains end up crossing between Llandogo and St Briavels, requiring that section to be relaid as double track. That can be remedied by making the 09:37 from Tidenham start at Monmouth and the 09:52 start from Tidenham rather than arrive from Monmouth, but then both Tidenham starters will want to be stabled at Tidenham at once. So probably best to stick with the above.) The WV(S) services are peak-summer special trains - probably to be steam hauled, although heritage electric trains are a possibility. They add another element to the mix - namely a requirement for Tidenham station to have two platforms. While two platforms will make the regular service much easier to operate, they will also cost a fortune - particularly since the timetable above will only really work if they are opposite each other with a footbridge (complete with two lifts - one at each end - and a roof) rather than end-to-end with a crossover in the middle. Tintern will be much easier to handle; a through line, loop and siding should be able to handle all the traffic. Consequently the third platform will not be required and will accordingly not be re-instated. WVR trains face a turn-around time at the Cardiff end of precisely 60 minutes; with suggestions having arisen about half-hourly trains to Maesteg (at the end of a branchline from Bridgend another 30 or so miles to the west) the set from Monmouth will probably end up running through to there. The two from Tidenham will just work the next train back to Tidenham half a hour later. Trains will run fairly late into the evening and the 90-minute journey time will open up the possibility of one set overnighting at Monmouth. Late night trains potentially allow Monmouth's youth to go to the bright lights of South Wales for the day rather than sit in the country grumbling that there's nothing to do. Whether we can persuade the traincrew to bring them back dead drunk at 2am is another matter. You will now see why we want a timetable before we lay out a signalling diagram. You will also see that timetabling is a highly entertaining mental exercise, which is why timetables are rarely recast and the results are usually viewed as worse than what was available before. If anyone would like to give our timetable writer a job re-writing timetables for decent pay he will probably be interested. |
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 Meet the latest version of the signalling diagram. It's not as basic as it could be, with four passing loops en route. The grey boxes mark the platforms around the passing loops and Redbrook level crossing; the halts (with the exception of Tutshill) have been omitted for convenience. The red dots mark Home signals (2 or 3 aspect); yellow dots mark Distant signals. The black lines represent tracks and the red crosses are level crossings. Tunnels and bridges are omitted. Being a signalling diagram, it's not to scale. The second platform at Tidenham will only go in if required - i.e. if the full timetable above is implemented. If a simple hourly Cardiff to Monmouth service is used it won't be necessary and so no loop or signalling (apart from the Home protecting the junction with the mainline and an associated Distant) will be provided. The loop at Tintern Quarry is intended to be generally useful in a miscellaneous kind of way; it will probably fail the cost/benefit analysis and get removed (or simply isolated; it would be much cheaper, if less tidy, to leave the track that's there in place to vanish under the vegetation that's currently taking it over). It would be used for crossing late-running passenger trains. Installing some signals here to break the Tintern to Tidenham section in half, even if no loop is provided, would help improve timetable resilience. The siding at Tintern consists of a headshunt for stabling stuff in (the steam service would work best with two locos; one would be laid up in the headshunt while the other takes the train to Tidenham and back) with a siding to connect to the vehicles currently parked by the extended former cattle dock. The crossing loop here is essential for the timetable above so is pretty much non-negotiable. St Briavels will get a loop for good measure. It doesn't allow for out-of-course running because there's no room for a platform on the loop line without removing the goods shed. The loop will allow said goods shed to be used for storing bits and pieces with direct access onto maintenance trains. (It does buildings good to have some kind of function in life.) In the exceedingly unlikely event that goods trains use the line again St Briavels will allow them to pass passenger trains; failing that, it will make it possible (if very awkward) to get the occasional special train north of Tintern between regular services. Lopping out the loop at Redbrook reduces land take and may just avoid having to demolish a house. The level crossing is hopefully easier to get in than the bridge but will need to be signalled - thus meaning that all four original stations will regain signalling, even if only two of them are guaranteed any trackwork. Monmouth Troy is marked with one platform plus a siding down the former Platform 2 here. The siding is not essential; it can, however, be used as a loop or for stabling those awkward special trains north of Tintern. It would also contribute to making Troy station look much more attractive. Should it be dropped, the signals will all disappear - with the exception of the Distant, which would become a large grey board with a picture of a distant signal on it. This would warn drivers of the presence of a bufferstop west of Troy station. Signalling could be controlled from Cardiff (like the mainline) but it would also be possible to arrange some form of control panel on the branch - although probably not worth it. Any such control panel would provide lots of lovely local employment (4 people) and reduce the line's chances of making a profit accordingly. However, it would also mean that when the mainline box is down (due to the weather, cable theft or a blown fuse) the branch would be able to continue operations. Tintern has the only surviving original signalbox but that makes a rather nice craft centre and isn't wholly suited to being converted to a modern 'box. The other likely possibilities are Tidenham and Monmouth. A box at Tidenham would probably be built into the new building. Monmouth would get a stand-alone affair pretending to be the original box.
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