Okehampton Railway re-opening

[phil-b259]

8 minutes ago, adb968008 said:

 

 

already said this doesnt need to be the case… a turnback siding just beyond the station would mean a single platform could suffice.

 

That doesn't help!

 

Nothing can access the turnback siding while a train is in possession of the St Beaudeaux - Tavistock token because to get there from the Gunnislake branch it has to encroach on the occupied section.

 

Thats why a completely separate Gunnislake platform is needed if you want to keep the signalling costs as low as possible but still provide both it and Tavistock with a decent service frequency

 

Personally I would be making serious representations that given every train stops at Bere Alston a foot crossing with miniature warning lights to access the 2nd platform would be a permissible departure from the normal stance that such things are prohibited - we did see one put in at braiding on the Isle of wight when that station got its passing loop put back recently.

Edited September 27, 2023 by phil-b259

[adb968008]

Just now, phil-b259 said:

 

In which case a Bourne End type setup would be possible at Bere Alston - however that would preclude through trains from Plymouth to Gunnislake (assuming that the St Beaudeax to Tavistock is regarded as a single token section*)

 

* If it becomes more complicated and Bere Alston becomes the meeting point for 3 token sections then I suspect the authorities would demand proper signalling be installed and not just traincrew operated groundframes + token machines...

Agreed,

 

But the Bottom line is some money would be needed, the line isnt going to grow itself and the developer money will only go so far.

 

The easy option is close Gunnislake, its only a 10 minute drive from Tavistock… That kind of threat may shake a money tree.

[Rivercider]

We have used the railway to get to Calstock on a couple of occasions (to walk from there along the Tamar to visit Cotehele NT).

One trip was planned by train to Plymouth, then change for the Gunnislake service. The other use of the train was only from Bere Alston to Calstock but we used the train precisely for the reason the Gunnislake branch was retained. We were staying at Tavistock and had planned to drive to Cotehele NT, but the day before our visit a lorry had damaged the bridge parapet where the A390 crosses the Tamar just to the north of Gunnislake, the bridge was closed to all traffic for several days . The road journey from Tavistock to Cotehele is about 8.5 miles over the A390 bridge, and about 15.5 miles including very narrow country lanes to get to the next river crossing to the north at Horsebridge, hence we used the train.

 

Here are a couple of views of Bere Alston from that trip in 2019.

Bere Alston from the down platform looking towards Plymouth. 17/4/2019

 

Bere Alston from the down platform looking north towards Tavistock 17/4/2019

 

 

Bere Alston from the down platform looking towards Plymouth, the Gunnislake branch diverges to the right. 17/4/2019

EDIT - and as pointed out by ADB968008 the ground frame is visible at the end of the platform ramp. 17/4/2019.

 

Also a gratuitous shot taken from the train as it crossed the Calstock Viaduct. 

Looking at the Tamar heading downstream, the walk to Cotehele NT follows the right hand bank (there was a horse drawn tramway alongside the river here with an incline up to the East Cornwall Mineral Railway. Cotehele NT is up in the trees off to the left where the river curves to the south. 17/4/2019.  

 

cheers

Edited September 27, 2023 by Rivercider
Edit caption to mention the ground frame.

[Jeremy Cumberland]

12 minutes ago, Mike_Walker said:

In theory, yes.  But...  You would still need some signalling to prevent a second train entering the station when the first is already in the station or on the other line.  Just saying they are timetabled sometime apart isn't acceptable, any train can run out of course.

Thank you, What I was wondering about was the existing arrangement. Are the points left set for Gunnislake while the train travels to Gunnislake and back?

[adb968008]

2 minutes ago, Jeremy Cumberland said:

Thank you, What I was wondering about was the existing arrangement. Are the points left set for Gunnislake while the train travels to Gunnislake and back?

 it has to be…

 

The unit cannot get out or back to Bere Alston without crossing the points… it would need to stop outside the station to reset them, in both directions on the Gunnislake branch, for what would be a relatively non-sensical reason to change them.

 

 

Edited September 27, 2023 by adb968008

[Mike_Walker]

7 minutes ago, adb968008 said:

 

 

already said this doesnt need to be the case.

But it would.  The only way to get a second platform at BA is to reinstate the former Up one.  To access this would require passengers to cross the line which means a footbridge as no one is going to sanction a new foot crossing in this day and age - they are trying to get rid of them wherever they can.  Lifts aren't a requirement as the bridge could have ramps rather than steps to make it accessible.  Lifts would require the station to be manned during operating hours in case of failures.

 

Even if the old Up platform reverted to being an island as it used to be and the present former Down platform abandoned there would still be the question of passengers having to cross the line to Tavistock.

 

I can assure you that a lot of highly qualified engineering and operating staff have been pondering this and have yet to come up with a cost effective, workable solution.  So what chance do we amateurs have?

[adb968008]

3 minutes ago, Rivercider said:

 

 

 

The ground frame is visible here, at the platform end.

Looking towards Plymouth (left) and Gunnislake (right).

[adb968008]

7 minutes ago, Mike_Walker said:

But it would.  The only way to get a second platform at BA is to reinstate the former Up one.  To access this would require passengers to cross the line which means a footbridge as no one is going to sanction a new foot crossing in this day and age - they are trying to get rid of them wherever they can.  Lifts aren't a requirement as the bridge could have ramps rather than steps to make it accessible.  Lifts would require the station to be manned during operating hours in case of failures.

 

Even if the old Up platform reverted to being an island as it used to be and the present former Down platform abandoned there would still be the question of passengers having to cross the line to Tavistock.

 

I can assure you that a lot of highly qualified engineering and operating staff have been pondering this and have yet to come up with a cost effective, workable solution.  So what chance do we amateurs have?

No it doesnt…

 

Excuse my fag packet drawing…

Red line.. Gunnislake.

Yellow line Plymouth to Tavistock.

Green.. Bere Alston Platform.

 

by adding a turnback off the end of the platform ( Blue), to the old goods yard, you can put in a unit running a shuttle between Gunnislake and Bere Alston. It can sit there shilst the driver/guard changes ends and inbetween a service arriving / departing Bere Alston in either direction from Plymouth to Tavistock.

 

This means your still a 1 platform operation.

Edited September 27, 2023 by adb968008

[Mike_Walker]

There is another example of this kind of reversal and that is the Looe branch.  This too has no signals and is in two sections.  Liskeard to Coombe Junction is NST with the token released by the Liskeard Bobby and Coombe Junction to Looe is a Train Staff.  The points are set by a GF at Coombe Junction unlocked by the token and worked by the traincrew.  The staff is captive in the frame and can only be removed when the road is set for Looe.  

[Mike_Walker]

2 minutes ago, adb968008 said:

No it doesnt…

 

Excuse my fag packet drawing…

Red line.. Gunnislake.

Yellow line Plymouth to Tavistock.

Green.. Bere Alston Platform.

 

by adding a turnback off the end of the platform, to the old goods yard, you can out in a unit running a shuttle between Gunnislake and Bere Alston. It can sit there shilst the driver/guard changes ends and inbetween a service arriving / departing Bere Alston in either direction from Plymouth to Tavistock.

But again it needs some form of signalling to prevent the possibility of two trains colliding.  However remote, it has to be taken into consideration.

Edited September 27, 2023 by Mike_Walker

[adb968008]

2 minutes ago, Mike_Walker said:

But again it needs some form of signalling to prevent the possibility of two trains colliding.  However remote, it has to be taken into consideration.

I dont see how its possible to run both Gunnislake and Tavistock with an hourly service without signalling…

Someone needs to pony up somewhere… the idea the line will grow itself naturally is for the birds surely no one thinks that this is free ?

 

 

Edited September 27, 2023 by adb968008

[Mike_Walker]

13 minutes ago, Rivercider said:

 

Looking at the Tamar heading downstream, the walk to Cotehele NT follows the right hand bank (there was a horse drawn tramway alongside the river here with an incline up to the East Cornwall Mineral Railway. Cotehele NT is up in the trees off to the left where the river curves to the south. 17/4/2019.  

 

cheers

That line of buoys down the river marks the boundary - please have your passports ready for inspection by Kernow Immigration officials.

[adb968008]

1 hour ago, Mike_Walker said:

There is another example of this kind of reversal and that is the Looe branch.  This too has no signals and is in two sections.  Liskeard to Coombe Junction is NST with the token released by the Liskeard Bobby and Coombe Junction to Looe is a Train Staff.  The points are set by a GF at Coombe Junction unlocked by the token and worked by the traincrew.  The staff is captive in the frame and can only be removed when the road is set for Looe.  

 

I was a rare passenger at Coome Junction Halt a few weeks ago.

 

I had to attract the drivers attention, as he stopped by the junction, and put his reds on to reverse.. he wasnt going to go those extra yards… as the guard put it, We were two more passengers than usual.

 

 

Edited September 27, 2023 by adb968008

[Mike_Walker]

2 minutes ago, adb968008 said:

I dont see how its possible to run both Gunnislake and Tavistock with an hourly service without signalling…

Someone needs to pony up somewhere… the idea the line will grow itself naturally is for the birds surely no one thinks that this is free ?

 

 

Maybe.  Has it not come to your notice that the Treasury is starving the UK rail industry of funding?

 

CP7 is coming.  The money available for that 5 year period is only about 60% of what was available in CP6 and it doesn't even allow for inflation.  The Government controls the purse strings, not NR or the TOCs - the latter have to get DfT approval for any expenditure over £500!

[Jeremy Cumberland]

54 minutes ago, adb968008 said:

Plymouth to St Budeaux is the mainline ..9 minutes.

St Budeaux to Bere Alston is quite fast.. 13 minutes.

its the Bere Alston to Gunnislake part that slows it down… 20 mins each way.

 

i’d imagine if Tavistock was built to similar line speed as the Lower section, an hourly to Tavistock would definitely be possible, though it would probably need a second unit and pass between Plymouth and St Budeaux, but it would also preclude Gunnislake services in the current one line operation without some extra infrastructure.

Don't forget that branch trains need to clear the junction between St Budeaux and Keyham, even if it isn't part of the single line section. I'd been using Keyham as my timing point, with 16 minutes to Bere Alston, which appeared to make an hourly service impossible. Omitting the stop at Bere Ferrers might get this down to 14 minutes, but that still only give 13 minutes for Bere Alston to Tavistock, Is that enough?

 

In my earlier posts, I had ruled this out as being too tight, which is why I hadn't given much thought for how to integrate a Gunnislake service into this pattern, which looks to be difficult/expensive whichever way it is done. Besides which, the image below shows 1 tph to Tavistock omitting Bere Ferrers and 0.5 tph to Gunnislake including Bere Ferrers. How is that expected to work without any signalling?

 

  

On 22/09/2023 at 07:55, Not Jeremy said:

This image from the Facebook group.

 

 

 

 

[009 micro modeller]

1 hour ago, Jeremy Cumberland said:

But what use is a 3-hour service? Northmoor didn't like even a 2-hour service:

Also isn’t it 2-hourly currently? So 3-hourly would actually be worse, even if it did go to Tavistock.

 

1 hour ago, Jeremy Cumberland said:

No. You could do Plymouth - Gunnislake - Tavistock - Plymouth (or Plymouth -Tavistock - Gunnislake - Plymouth) as a 2-hourly service if Bere Alston - Tavistock - Bere Alston can be done in less than 30 minutes, but you can't do the double-Thurso thing to either destination.

 

Perhaps a more viable "no signalling" option would be alternate services to Gunnislake and Tavistock on a 3-hourly frequency with the pattern:

1. Keyham to Gunnislake to Keyham
2. Keyham to Tavistock to Keyham

Why would you terminate at Keyham? To decrease the overall journey time?

 

Is Thurso actually served twice? I suppose it is if you take into account the return working. Obviously Georgemas is (and Bere Alston would be under the ideas being discussed here). I thought on the Far North line this is largely done to remove the need to split the train at Georgemas (as was done in the past) so the train just goes to Thurso first and then back to Georgemas, and then to Wick. But is the bonus result of having a few direct Thurso to Wick trains also thought to be important? The pattern you suggest would probably work better for 2-hourly but the detour to Tavistock (or Gunnislake - whichever is served first; maybe this could alternate) would make the frequency at intermediate stations a bit irregular.

[adb968008]

38 minutes ago, 009 micro modeller said:

Also isn’t it 2-hourly currently? So 3-hourly would actually be worse, even if it did go to Tavistock.

 

Why would you terminate at Keyham? To decrease the overall journey time?

 

Is Thurso actually served twice? I suppose it is if you take into account the return working. Obviously Georgemas is (and Bere Alston would be under the ideas being discussed here). I thought on the Far North line this is largely done to remove the need to split the train at Georgemas (as was done in the past) so the train just goes to Thurso first and then back to Georgemas, and then to Wick. But is the bonus result of having a few direct Thurso to Wick trains also thought to be important? The pattern you suggest would probably work better for 2-hourly but the detour to Tavistock (or Gunnislake - whichever is served first; maybe this could alternate) would make the frequency at intermediate stations a bit irregular.

Its worth pointing out that hardly anyone is ever on those Thurso trains, and a lot detrain at Georgemas to cars, friends and taxis, to save time going to Thurso, only to go back to Wick.

 

 

Edited September 27, 2023 by adb968008

[phil-b259]

1 hour ago, adb968008 said:

No it doesnt…

 

Excuse my fag packet drawing…

Red line.. Gunnislake.

Yellow line Plymouth to Tavistock.

Green.. Bere Alston Platform.

 

by adding a turnback off the end of the platform ( Blue), to the old goods yard, you can put in a unit running a shuttle between Gunnislake and Bere Alston. It can sit there shilst the driver/guard changes ends and inbetween a service arriving / departing Bere Alston in either direction from Plymouth to Tavistock.

 

This means your still a 1 platform operation.

 

And how pray tell do you signal that layout with just crew opperated ground frames and single line tokens!

 

Remember the current setup requires no signals precisely because all movements happen within the area covered by a single token and only one train can be in that section at a time!

 

The minute you have two trains needing to share a single piece of track (regardless how short) the no signals token system cannot be implemented. 

 

Places like Bourne End can get away with no signals and two trains because each train is locked into its own piece of track and cannot possibly end up crashing into the other - something that is impossible to guarantee in your design without proper signalling being needed.

 

 

[Reorte]

3 minutes ago, phil-b259 said:

Places like Bourne End can get away with no signals and two trains because each train is locked into its own piece of track and cannot possibly end up crashing into the other - something that is impossible to guarantee in your design without proper signalling being needed.

So what would be the equivalent in this case? One train locked in to Bere Alston - Gunnislake (or Bere Alston - Tavistock)? Doesn't sound terribly practical (and I appreciate you're not trying to suggest that it would be).

[Jeremy Cumberland]

59 minutes ago, 009 micro modeller said:

Why would you terminate at Keyham?

I wouldn't, but trains can't cross at St Budeaux Victoria Road, because its only a single line, so you have to take timings from further east, on the double track main line. Plus you have to allow time between signalling one train off the branch and signalling the next one onto it. This might be less than a minute, but minutes look to be very important if you are trying to provide an hourly service to Tavistock.

 

To be on the safe side, I used the Keyham times. This gives 6 minutes between a train leaving St Budeaux Victoria Road for Plymouth and the next branch train leaving St Budeaux Victoria Road for Bere Alston (including collecting the token). This might be longer than is actually needed, but not by much I think.

 

59 minutes ago, 009 micro modeller said:

Is Thurso actually served twice?

Yes, but Thurso is only 10 minutes from Georgemas Junction. The whole rigmarole takes 25 minutes in each direction. I forget how long was allowed for splitting and joining units, but it probably adds 20 minutes to the journey time to/from Wick compared with splitting.

 

59 minutes ago, 009 micro modeller said:

Obviously Georgemas is

If you are looking at a return journey from Inverness, Georgemas Junction is served four times.

 

59 minutes ago, 009 micro modeller said:

But is the bonus result of having a few direct Thurso to Wick trains also thought to be important?

No, not at all, but trains don't arrive at Wick and then leave straight away (presumably the driver needs a break, for a start). Typically they wait there for about an hour. This pretty much rules out a triangular service of Inverness - Wick - Thurso - Inverness (or Inverness - Thurso - Wick - Inverness).

 

10 minutes ago, phil-b259 said:

Places like Bourne End can get away with no signals and two trains because each train is locked into its own piece of track and cannot possibly end up crashing into the other

Bourne End does have signals, and rather a lot of signalling, as Mike Walker explains:

  

2 hours ago, Mike_Walker said:

Not exactly.  It's two sections, Maidenhead to Bourne End protected by No Signaller Token (NST) working and Bourne End to Marlow with a Train Staff.  There is a Ground Switch Panel at Bourne End and motorised points with point indicator signals.  The GSP is operated by the traincrew in co-operation with the signaller at the TVSC.  This allows a two train service in the peaks with one train shuttling from Bourne End to Marlow and the other to Maidenhead - there are two platforms at Bourne End.

There'll also be a token instrument for the section from Maidenhead.

[cctransuk]

1 minute ago, adb968008 said:

I guess this is why after 10 years, a simple 6 mile siding on an existing formation doesnt exist and you wonder why non industry people look at this industry as an albatross.

 

....

 and why the French can build an entire network of high speed railways in the time it takes us to build one and a bit!

 

CJI.

[phil-b259]

28 minutes ago, Reorte said:

So what would be the equivalent in this case? One train locked in to Bere Alston - Gunnislake (or Bere Alston - Tavistock)? Doesn't sound terribly practical (and I appreciate you're not trying to suggest that it would be).

 

Yes thats exactly what I'm suggesting.

 

When the unit for Gunnislake arrives in the morning, the crew remove a token for the Gunnislake branch (thus proving it is empty of trains*) and use the St Budeaux - Tavistock token to operate the ground frame and access the branch. Once this manoeuvre has been done the crew reset the ground frame, withdrawing the St Budeaux - Tavistock token and puutiing that in a intermediate token instrument at Bere Alston. This allows another train from Plymouth to then be given a fresh St Budeaux - Tavistock token.

 

The Gunnislake unit then simply shuttles between its own platform at Bere Alston and Gunnislake all day on its own track and kept completely separate from the St Budeaux - Tavistock line.

 

At the end of the day the startup[ procedure is reversed, once the train from Tavistick has exited the branch onto the main line to Plymouth, the crew on the Gunnislake shuttle can obtain a St Budeaux - Tavistock token from the instrument at Bere Alston, opperate the ground frame to release the unit, reset the Ground frame, return the Gunnislake token back to its instrument then head back to Plymouth

 

* This step is necessary so as to prevent the ground frame being erroneously released by a St Budeaux - Tavistock train while a train is opperating on the Gunnislake branch and thereby causing a potential collision. 

 

The point about this operation is that apart from 1 mechanical ground frame and a couple of token machines there there is NO signalling equipment required! - therefore it is CHEAP to implement.

 

The only issue here is the need for passengers to be able to cross the Tavistock line to reach the 2nd platform. Although the regulations are quite clear that foot crossings should not be used - if they are that sacrosanct please tell me how come Braiding on the Isle of Wight saw just such a foot crossing opened up when the loop was put back in so as to avoid the cost of a ramped footbridge or lifts!

 

As such I would say a president has been set and given all services are schedules to stop at Bere Alston, a minuture warning light foot crossing should be allowed as a 'special case'

Edited September 27, 2023 by phil-b259

[The Stationmaster]

21 hours ago, adb968008 said:

couldnt they just run Gunnislake as a shuttle from Bere Alston ?

Put in a turnback siding just beyond the Tavistock end of the platform, so that way it remains a single platform operation.

They could and it wouldn't be the most expensive oprion .  But what it would them mean is that the Tavistock trains would have to call at all stations Plymouth - Bere Alston in order to cover the stops that would be lost by taking away the Gunnislake trains.

 

So it would really then come down to what is seen as commercially attractive in terms of journey time between Tavistock and Plymouth and whether a workable hourly interval could be achieved without additional infrastructure costs.  To be commercially effective the Tavistock link has to offer a journey time and frequency which is attractive enough to get people out of their cars and that means a minimum of intermediate stops .

 

Apart from upsetting the tree huggers by removing numerous trees on the Up side at the station it wouldn't be a really difficult infrastructure job at Bere Alston.  Operationally it will simply mean the Gunnislake train sits there for ages waiting for the next train from Tavvy to connect with as it can't get there in time to connect with the back working of the train it connected out of.  Of course the attraction of a rail trip to Gunnislake might well decrease if it involves a change at Bere Alston.

 

 I doubt if Tavistock would be a commercial success with a less than hourly frequency if the railway does what it is meant to do.  One thing which gets quickly lost in all of this is the practicalities that exist beyond the headline of 'reopening to Tavistock'.  These practicalities are part of what has killed the idea on several occasions over the past 30+ years because they are the stage at which the costs - now far greater than they were 30 years ago - come out of the woodwork.

 

So time now for some facts and a few estimates of how the trains service could be worked

 

Currently trains are booked 15 minutes for the 7miles 17chs  from St Budeax Jcn (pass) to Bere Alstom=n (stop/start) in both directions. Maximum line speed is 55 mph but there are various permanent restrictions down to 25 mph (at St Budeaux), and 40 mph elsewhere plus 20 mph approaching Bere Alston.  The line is heavily graded, basically rising most of the way towards Bere Alston with a maximum of 1in73.  There is one User Worked Crossing (a farm crossing)

 

Although the station site is not entirely clear at Tavistock the old station was 6 miles  41 chs from Bere Alston.  Again the line is heavily graded and had a maximum gradient of 1in75 but it is not consistently rising so heavy rising gradients are encountered in both directions.  Shillamill Tunnel, just over 3 miles from Bere Alston lies on a 1in98 gradient and is 603 yards long (presumably it has no resident bats?).

 

As it would be  all new track laid to modern standards and making full use of the formation I would look for a line speed of at least 60 mph on this section and preferably 75mph where practicable (although the higher speed might increase cost.  So a running (start-stop) of c.8.5 minutes (possibly a little less depending on station site) should be achievable between Bere Alston and Tavistock. Thus with a 1 minute dwell at Bere Alston and no line speed improvement between there and St Budeaux Jcn a c.23-24 minute running time should be achievable between St Budeaux Jcn and Tavistock with intermediate stops at St Budeaux and Bere Alstion.  With a 5 minute turnround at Tavistock that gives a cycle time from St Budeaux Jcn - Tavistock and return of c .53 minutes, possibly a little less.  That is sufficient margin for the next train to Tavistock to enter the single line at St Budeaux Jcn and thus maintain an hourly interval from North Road to Tavistock.

 

It also allows a 22 minute gap for a Gunnislake train to run in either direction (but not both) between St Budeaux and Bere Alston while the Tavistock train is between Bere Alston and Tavistock  but this requires a quite extensive installation of signals ar Bere Alston in order to create the necessary protection between the trains with suitable overlaps in order to allow a Gunnislake train to enter the single line at St Budeaux while the train to Tavistock is still at Bere Alston.  The result, even if additional signals are added, would be to create a very tight timetable which would be very prone to perturbation and ever increasing reactionary delays.

 

In order to get a more reliable timetable a dynamic passing loop would be required in the vicinity of Bere Ferrters.  If that is not provided you can forget having Plymouth to Gunnislake trains and a reliable service to Tavistock.   An alternative might be to have two platforms at Bere Alston with an extended loop of a couple of miles but then you are into a very expensive footbridge with ramps or lifts plus the cost of maintaining two platforms. 

 

At present the line is still presumably opearted on a One Train Only basis with teh Train Staff held in an instrument at St Budeaux Victoria Road station (halt?) .  What is in. mind for the line when Plymouth resignalling is developed might see this change but as design work has (so I'm informed) not yet underway changes are simple to make.  Making changes after resignalling is completed will cost a lot, lot, more.

 

 

 

[phil-b259]

6 minutes ago, Jeremy Cumberland said:

 

 

Bourne End does have signals, and rather a lot of signalling, as Mike Walker explains:

  

 

Those are NOT signals!

 

Although they look like signals ALL they do is confirm that the points have properly moved over to the correct position and are not standing half way position to derail the train. They are NOT interlocked with the token instruments or track circuits like true signals are! Hence the need for the supplementary plate reminding the driver they must be in possession of the correct token before proceeding.

[The Stationmaster]

2 hours ago, Mike_Walker said:

But it would.  The only way to get a second platform at BA is to reinstate the former Up one.  To access this would require passengers to cross the line which means a footbridge as no one is going to sanction a new foot crossing in this day and age - they are trying to get rid of them wherever they can.  Lifts aren't a requirement as the bridge could have ramps rather than steps to make it accessible.  Lifts would require the station to be manned during operating hours in case of failures.

 

Even if the old Up platform reverted to being an island as it used to be and the present former Down platform abandoned there would still be the question of passengers having to cross the line to Tavistock.

 

I can assure you that a lot of highly qualified engineering and operating staff have been pondering this and have yet to come up with a cost effective, workable solution.  So what chance do we amateurs have?

There is no longer a requirement to man a station during opening hours if it has lifts.  However suitable emergency call arrangements have to be installed in the lifts and there might be some sort of limit on a minimum time  that has to be allowed for 'someone' to attend when problems arise.

 

Example - Twyford - where the station can be left unmanned during train operating hours with the lifts still available for use (even if one of the lifts is happy to tell users that it is going from platform level to the subway when you join it on the footbridge!!)..

 

And yes Mike - I had a go at trying to resolve the conundrum of adding Tavistock trains to the route a bit over 30 years ago.  The basic laws of physics and time have not changed since then even if we do now know what a black hole looks like (the clue is in the name)