East West Mainline interchanges

[sammorris]

Even with that i still think a reversal at Bletchley is the easiest way to facilitate that service!

To me that's the fundamental point. Leaving aside all the detail arguments about specific bridges etc., and even taking generally the most optimistic assumptions about everything (i.e., even assuming you could debunk every last objection A0wen has listed), I still don't see the sort of advantages for building a chord which would be needed to justify the very large costs. You can still have the service via a reversal. Yes, expensive works might well be needed to provide a path for that, but even if very extensive they'd be at least an order of magnitude less expensive than building a chord, I'd have thought.

First off, Bletchley is still in the urban area of Milton Keynes, and I think MK residents would probably drive to it (or catch a bus) for the longer distance services to the East (and indeed West, probably).

Second, there's a lot of people talking about interchange of long distance EWR services with long distance WCML services at MKC. But it seems to me this is a bit of a red herring really, because if you're coming from Oxford or St Neots or Cambridge - there are other reasonable routes to the north and midlands anyway. We're talking about passengers from Bedford and closer, perhaps plus some people changing at Bedford from other nearby MML stations. For any potential commuting to offices - we are also talking about passengers from the same stations, mainly Bedford and closer. I suspect many (most?) people on any longer distance EWR service would actually find services making a detour into MKC and back to be a nuisance.

So - the train with overwhelmingly the strongest case for extending to MKC from the Bedford direction is the local service, and that service would clearly want a stop at Bletchley too... which it would skip if it went on this suggested chord. I'm really struggling to see the value of it...

 

[richieb1971]

The EWR railway will grow into what it needs to be I'm sure.

But the connecting trains issue is well below expectations with Cambridge and Oxford the only 2 places that are as expected being they are terminus stations for this line.

 

[AlbertBeale]

To me that's the fundamental point. Leaving aside all the detail arguments about specific bridges etc., and even taking generally the most optimistic assumptions about everything (i.e., even assuming you could debunk every last objection A0wen has listed), I still don't see the sort of advantages for building a chord which would be needed to justify the very large costs. You can still have the service via a reversal. Yes, expensive works might well be needed to provide a path for that, but even if very extensive they'd be at least an order of magnitude less expensive than building a chord, I'd have thought.

First off, Bletchley is still in the urban area of Milton Keynes, and I think MK residents would probably drive to it (or catch a bus) for the longer distance services to the East (and indeed West, probably).

Second, there's a lot of people talking about interchange of long distance EWR services with long distance WCML services at MKC. But it seems to me this is a bit of a red herring really, because if you're coming from Oxford or St Neots or Cambridge - there are other reasonable routes to the north and midlands anyway. We're talking about passengers from Bedford and closer, perhaps plus some people changing at Bedford from other nearby MML stations. For any potential commuting to offices - we are also talking about passengers from the same stations, mainly Bedford and closer. I suspect many (most?) people on any longer distance EWR service would actually find services making a detour into MKC and back to be a nuisance.

So - the train with overwhelmingly the strongest case for extending to MKC from the Bedford direction is the local service, and that service would clearly want a stop at Bletchley too... which it would skip if it went on this suggested chord. I'm really struggling to see the value of it...

Without knowing the local demographics etc myself, I nevertheless find this logic makes sense - ie the main case for trains from the east serving MKC is probably for the local stopping services, which would need to serve Bletchley too. So they'd have to reverse anyway, and the extra chord would't be needed (however useful it owuld be in the long term, including for possible freight etc). Of course this reversal needn't block the new high-level station and get in the way of through E-W services, since such trains could run into the existing low-level terminus and reverse back north from there.

And given that some trains from the west will go on to MKC from Bletchley anyway, maybe the extra chord is unnecessary for now. But the logic might change if the line ever continues east from Bedford on to Cambridge. Would it make sense for half the services from the western end of EWR being diverted to MKC, without any option for those from the east to do so too, so leaving the eastern end of the line with only half the service level of the western end?

 

[Nottingham59]

The EWR railway will grow into what it needs to be I'm sure.

I'm not convinced it will. This image shows the night-time view of SE England, with Birmingham at the top left. The bigger blobs in a line between Birmingham and London are Coventry, Rugby (faint), Northampton, Milton Keynes and Dunstable/Luton.


Oxford (at 7 o'clock from MK) is pretty small, and Bicester between them is tiny. Bedford (at 2 o'clock) is not much bigger than Oxford, and Cambridge is no bigger and much further away. Aylesbury (6 o'clock) is pretty small too. I'm afraid to say that I can't see how EWR is ever going to generate much traffic between these centres.

There may be scope for intermodal freight from Southampton to avoid Birmingham, and there will be a few longer journeys where changing onto EWR makes sense. But enough to fill half a dozen 4-car EMUs per hour?

 

[A0]

TBF, I don't think the limited-stop service is proving controversial, it's the station relocations and consolodations that are. With the planned infrastructure they are intrinsically linked, but they don't have to be. Putting the removed freight loops back in and enhancing them to passenger-grade (and in all likelihood, extending them into dyanmic loops) would give some scope for overtaking. It would be ludicrous gold-plating, but it would be ideal to have loops or through lines at every station. At the very least I wish they'd leave passive provision for them when rebuilding any stations, but that was clearly never on the cards.

The reality is whilst the line has 10 intermediate stations - many of which are *very* lightly used, they will be a block to running better services without alot of expensive extra track work.

Just to put it in context, here are the usage figures (in 000s) for each of the stations (2019 as the last "normal" year).

Fenny Stratford 26.4
Bow Brickhill 41.3
Woburn Sands 7.5
Aspley Guise 9.4
Ridgmont 26.2
Lidlington 19.2
Millbrook 12.2
Stewartby 72.7
Kempston Hardwick 10.5
Bedford St Johns 180.5

To put it in context any station with a use of 20.0 would on average be seeing about 60 people a day. On a 36 train a day service (2 trains an hour, one each way) that equates to an average of 1.5 people boarding, which suggests some of those trains aren't picking up or dropping off anyone.

So I think there's a reasonable case for consolidation - and I'd probably look at Millbrook, Aspley Guise and Woburn Sands, possibly Kempston Hardwick and (with apologies to DarloRich) Fenny Stratford in the case of the latter because Bletchley station is about a mile away with relatively little housing north or east of it (which is further from Bletchley).

 

[richieb1971]

I'm not convinced it will. This image shows the night-time view of SE England, with Birmingham at the top left. The bigger blobs in a line between Birmingham and London are Coventry, Rugby (faint), Northampton, Milton Keynes and Dunstable/Luton.

View attachment 109767
Oxford (at 7 o'clock from MK) is pretty small, and Bicester between them is tiny. Bedford (at 2 o'clock) is not much bigger than Oxford, and Cambridge is no bigger and much further away. Aylesbury (6 o'clock) is pretty small too. I'm afraid to say that I can't see how EWR is ever going to generate much traffic between these centres.

There may be scope for intermodal freight from Southampton to avoid Birmingham, and there will be a few longer journeys where changing onto EWR makes sense. But enough to fill half a dozen 4-car EMUs per hour?

This is why the railway needs to be the greatest it can be. As a passenger only railway it only serves to provide connections from the main trunk routes and it doesn't do that very well under the current plans.

Its selling points -

Helps avoid London in most connecting scenarios
100mph end to end running (exception Marston Vale)
4tph (might be overkill)



Areas where it can be improved -

Connectivity to other services
Balancing East and West services to MKC
Improving EMR services at Bedford

More selling points
Developing a FOC/Depot relationship with a logistics haulier company somewhere along the line so that trucks do shorter distances
Reviewing/Purposing EWR for freight capability
Provisioning for divisionary routes by connecting northern facing junctions.
Finding a purpose for Stewartby/Forders sidings besides a loop


Still unknowns -

Blu prints for Bedford Midland station, something like we got for Bletchley.

Heavy speculative sellings points -

4tph is needed
Oxford/MKC has a larger customer base relationship
That people don't care about changing train to reach somewhere not on EWR
That EWR can be a successful venture on the mandated scope
Nobody knows the price of the tickets
That Bedford is somehow going to benefit from EWR in a positive way


Arguments for not using EWR -

Freight services are happily using pre existing routes
EWR is built as a passenger railway and as such will offer nothing beyond the scope of passenger services in the first instance
Green do gooders will not use it because its diesel propulsion
Building the railway is going to upset so many people so will unlikely use it

 

[A0]

This is why the railway needs to be the greatest it can be. As a passenger only railway it only serves to provide connections from the main trunk routes and it doesn't do that very well under the current plans.

Its selling points -

Helps avoid London in most connecting scenarios
100mph end to end running (exception Marston Vale)
4tph (might be overkill)



Areas where it can be improved -

Connectivity to other services
Balancing East and West services to MKC
Improving EMR services at Bedford

More selling points
Developing a FOC/Depot relationship with a logistics haulier company somewhere along the line so that trucks do shorter distances
Reviewing/Purposing EWR for freight capability
Provisioning for divisionary routes by connecting northern facing junctions.
Finding a purpose for Stewartby/Forders sidings besides a loop


Still unknowns -

Blu prints for Bedford Midland station, something like we got for Bletchley.

Heavy speculative sellings points -

4tph is needed
Oxford/MKC has a larger customer base relationship
That people don't care about changing train to reach somewhere not on EWR
That EWR can be a successful venture on the mandated scope
Nobody knows the price of the tickets
That Bedford is somehow going to benefit from EWR in a positive way


Arguments for not using EWR -

Freight services are happily using pre existing routes
EWR is built as a passenger railway and as such will offer nothing beyond the scope of passenger services in the first instance
Green do gooders will not use it because its diesel propulsion
Building the railway is going to upset so many people so will unlikely use it

You can forget "improving EMR services at Bedford".

EMR are not going to start slowing down Sheffield or Nottingham services to call at Bedford when there is virtually no demand to travel to Bedford from points north of Kettering. That change only benefits Bedford - London travellers if it ran non stop and Bedford is already getting 2TPH EMR to St Pancras. The only conceivable stop I could foresee EMR wanting on those fast from Kettering services is Luton Airport Parkway.

 

[richieb1971]

Just out of interest I assume any reversal at Bletchley would use the lower tier existing platforms right?

As for EMR I was hoping the Leeds Bedford service would get a nod. I travelled to Leicester recently and the switch at Kettering seemed clunky. Definitely a downgrade in service and the ticket was more expensive than my prior visit which was direct. EWR would no doubt increase traffic on interconnectivity alone.

A colleague at work used to travel Northampton to Nottingham via 3x train. Connectivity is an issue for the whole network. Taxi to Wellingborough was like 25 quid which seemed ridiculous to me so 3x train it was via Tamworth, Derby, Nottingham.

EMR 12 car trains are terribly utilized at the moment with 5 to 10 people per car. Not sure if 222s can do 12 car but that sounds better than the new trains with the change over at Kettering.

 

[Pigeon]

To be fair the Bubble cars were 20 or more years ago.

Sure, but as I say I just looked up the same commuting journey and if anything it's now slightly worse than it was then.

But the slow journey time is in large part due to the number of station stops over a relatively short journey ...
... To provide a "limited" stop service across the MV is already being proposed by EWR and is already proving controversial - so what's the answer ?

At the time, I was thinking of alternating the all-stations service with a "fast" service that only stopped at the most-used stations, so probably Stewartby, Lidlington and maybe Bow Brickhill. It wouldn't have been perfect, but it would have made a significant difference. With the all-stations service only being one train an hour there would have been plenty of room to run a one-per-hour main-stations-only service in the in between times. Or an alternative and possibly better way to arrange it might have been 2tph calling at all stations for half the line and running fast for the other half, alternating between which half is which.

With EWR in the picture it's the same basic question only with a compulsion to find an answer: somehow or other EWR services and MV stoppers are going to have to be interleaved, and it comes down to how much of the answer we get will be in providing the infrastructure (such as loops) to make this possible, and how much will be just fudging it and hoping.

 

[Bald Rick]

As for EMR I was hoping the Leeds Bedford service would get a nod.

That was a suggested post HS2 service, and frankly has no chance.

EMR 12 car trains are terribly utilized at the moment with 5 to 10 people per car.

There aren’t any EMR 12 car trains.

 

[richieb1971]

There aren’t any EMR 12 car trains.

I thought 360s were. Even worse then, 5 to 10 people per car on 8 car trains. At least when reaching Bedford.

 

[A0]

Just out of interest I assume any reversal at Bletchley would use the lower tier existing platforms right?

Yes, because in theory it could be done now (paths permitting).

As for EMR I was hoping the Leeds Bedford service would get a nod. I travelled to Leicester recently and the switch at Kettering seemed clunky. Definitely a downgrade in service and the ticket was more expensive than my prior visit which was direct. EWR would no doubt increase traffic on interconnectivity alone.

I thought the current EMR Leeds services had been binned? Didn't they remain because the HSTs were based at Neville Hill and since EMR don't have those any longer, they don't need to run to Leeds?

And a Leeds "stopper" from St P would be interminably slow.

A colleague at work used to travel Northampton to Nottingham via 3x train. Connectivity is an issue for the whole network. Taxi to Wellingborough was like 25 quid which seemed ridiculous to me so 3x train it was via Tamworth, Derby, Nottingham.

I assume said colleague doesn't drive or have a car on the basis of the taxi comment. Why they didn't just get the Stagecoach x7 to Market Harborough (45 mins) and train from Harborough direct to Nottingham ? (35 mins).

I thought 360s were. Even worse then, 5 to 10 people per car on 8 car trains. At least when reaching Bedford.

That's only since Covid. In rush hour if you were at Wellingborough each train was picking up at least 100 people - on trains which were full having started out a Notyingham or Sheffield. Even off peak you'd get a dozen or more on most daytime trains. Not sure you can use current volumes to prove your case - there are still alot of people not travelling.

== Doublepost prevention - post automatically merged: 5 Feb 2022 ==

At he time, I was thinking of alternating the all-stations service with a "fast" service that only stopped at the most-used stations, so probably Stewartby, Lidlington and maybe Bow Brickhill. It wouldn't have been perfect, but it would have made a significant difference. With the all-stations service only being one train an hour there would have been plenty of room to run a one-per-hour main-stations-only service in the in between times. Or an alternative and possibly better way to arrange it might have been 2tph calling at all stations for half the line and running fast for the other half, alternating between which half is which.
.

To run 2tph on the MV, would increas the number of units you'd need from 2 to 3 (maybe 4) and the same of staffing.

This on a line which, judging by the pre Covid loadings, I struggle to believe even comes close to covering its costs - that would make it even worse.

 

[Class 170101]

Do you really need 1000m radius for a reduced speed curve, lets say 40mph max for simplicity.
The curve wouldn't be meant for an intermodal going full pelt.

This below edwin_m is correct

I think the 1000m was the length between the junctions either end of the curve, not the radius of the curve itself. Similar to the Bacon Factory Curve in Ipswich, this would allow a train to wait for a path onwards, without blocking other trains behind it that are going into Bletchley station.

However

However, and entirely theoretically as none of this is likely to happen, I imagine a long loop somewhere in open county on the eastern approaches to Bletchley would do the job nearly as well for westbound trains off EWR, so they could be recessed until a path was available round the curve and onto the WCML. A loop in the same place for eastbound would be somewhat less satisfactory as trains from WCML onto EWR would have to have a path as far as that loop, but might still be good enough.

This may or may not work, the reason for the chord being 1000m long is to recess Freight waiting for paths to match between EWR and WCML. A westbound loop on the EWR may still face the same problems, as a westbound to northbound freight would still need to cross the eastbound EWR and the Southbound WCML slow line and you would need to match both up for crossing slots without the 1000m+ chord in the middle.

 

[Dr Hoo]

There is also the issue that if the hypothetical chord was used to 'hold' long freights between the EWR and WCML it would then seriously reduce the scope to run any passenger services that way as well.

Similar to the fact that the to-be-extended (single track) Dore South Curve will be used to regulate long freights to and from the Hope Valley, thereby preventing any ambitions for a fast Chesterfield-Manchester link avoiding a Sheffield reversal.

The 'Bacon Factory' curve at Ipswich is purely intended for freight so no 'competition' with passenger capacity arises.

Any East-North curve at Bletchley would really need to be four track with essentially freight 'loops' in either direction. On top of the minimum sensible length of 1,000m this would start getting into serious cost territory rather than being 'for the sake of a few quid'/'spoiling the ship for a ha'porth of tar'.

 

[The Planner]

There is also the issue that if the hypothetical chord was used to 'hold' long freights between the EWR and WCML it would then seriously reduce the scope to run any passenger services that way as well.

Similar to the fact that the to-be-extended (single track) Dore South Curve will be used to regulate long freights to and from the Hope Valley, thereby preventing any ambitions for a fast Chesterfield-Manchester link avoiding a Sheffield reversal.

The 'Bacon Factory' curve at Ipswich is purely intended for freight so no 'competition' with passenger capacity arises.

Any East-North curve at Bletchley would really need to be four track with essentially freight 'loops' in either direction. On top of the minimum sensible length of 1,000m this would start getting into serious cost territory rather than being 'for the sake of a few quid'/'spoiling the ship for a ha'porth of tar'.

It would never happen. A single line chord is currently flimsy at best.

 

[richieb1971]

Surely post HS2 the slow tracks around MkC will be primarily ewr and freight.

The 2 tracks west of MkC you need are hs2.

 

[Bald Rick]

Surely post HS2 the slow tracks around MkC will be primarily ewr and freight.

The 2 tracks west of MkC you need are hs2.

Off peak, 3 “WMT”, 1 “Southern”, and 5 freight on the slows Bletchley to MK.

 

[richieb1971]

Off peak, 3 “WMT”, 1 “Southern”, and 5 freight on the slows Bletchley to MK.

Is that per hour?

Is that post HS2?

Most passenger traffic can use WCML fasts Post HS2 as the Birmingham fasts won't run, or will they?

Either way 1 single additional track to MkC from EWR should be enough for the mile shuttle runs they will do. There is only 1 bay platform at MkC anyway.

 

[Bald Rick]

Is that per hour?

Is that post HS2?

Yes.

Most passenger traffic can use WCML fasts Post HS2 as the Birmingham fasts won't run, or will they?

No they can’t. They’ll be 4 x “Avanti” services (2 West Mids, 1 Manchester via Stoke, 1 Chester), and 2 “WMR” on the fasts at MK, plus a third (and possibly a fourth) on the fasts south of Ledburn Jn.

 

[Cantab26]

Either way 1 single additional track to MkC from EWR should be enough for the mile shuttle runs they will do. There is only 1 bay platform at MkC anyway.

How many trains per hour in each direction will your single track accommodate?

 

[hooverboy]

There is also the issue that if the hypothetical chord was used to 'hold' long freights between the EWR and WCML it would then seriously reduce the scope to run any passenger services that way as well.

Similar to the fact that the to-be-extended (single track) Dore South Curve will be used to regulate long freights to and from the Hope Valley, thereby preventing any ambitions for a fast Chesterfield-Manchester link avoiding a Sheffield reversal.

The 'Bacon Factory' curve at Ipswich is purely intended for freight so no 'competition' with passenger capacity arises.

Any East-North curve at Bletchley would really need to be four track with essentially freight 'loops' in either direction. On top of the minimum sensible length of 1,000m this would start getting into serious cost territory rather than being 'for the sake of a few quid'/'spoiling the ship for a ha'porth of tar'.

hence why I had suggested retaining the bedford st johns- stewartby section. for use as a freight holding loop and "parliamentary" stoppers.
The main EWR rroute from BDM going from the midland mainline @ elstow and joinging marston vale just east of stewartby.
no need for an additional big radius cuvre at the bletchley end.

 

[hooverboy]

How many trains per hour in each direction will your single track accommodate?

With 1 bay platform, plus the 3 or 4 mile run up/down the WCML slows, 2 trains per hour would be feasible.

 

[richieb1971]

How many trains per hour in each direction will your single track accommodate?

I don't see any reason why the extra track won't just accomodate the bay platform at MKC. Since that is what its going to be used for.

EWR is passenger only right? There is no north curve from the East apparently. So you have a train going to MKC and that same train coming out. Why would you need 2 or more tracks for just that?

 

[Cantab26]

I don't see any reason why the extra track won't just accomodate the bay platform at MKC. Since that is what its going to be used for.

EWR is passenger only right? There is no north curve from the East apparently. So you have a train going to MKC and that same train coming out. Why would you need 2 or more tracks for just that?

Let’s try again:

How many trains per hour in each direction will your single track accommodate?

 

[richieb1971]

Let’s try again:

How many trains per hour in each direction will your single track accommodate?

I don't know the timetables. If Oxford to MKC is 1 train per hour, then 1 train per hour in, and the same train out again.
This one track is a pretty big ask considering the first 1 min of this video.

 

[Cantab26]

I don't know the timetables. If Oxford to MKC is 1 train per hour, then 1 train per hour in, and the same train out again.
This one track is a pretty big ask considering the first 1 min of this video.

Try 2tph in each direction between Oxford and Milton Keynes Central plus an aspiration for at least 1tph to/from Aylesbury.

And you are, I believe, proposing that services also run between Bedford and Milton Keynes Central.

Really rather tight on a single line of this length.

Whereas if there is only one train in each direction per hour, that seems a rather expensive bit of infrastructure that isn’t being used for very much.

== Doublepost prevention - post automatically merged: 5 Feb 2022 ==

hence why I had suggested retaining the bedford st johns- stewartby section. for use as a freight holding loop and "parliamentary" stoppers.
The main EWR rroute from BDM going from the midland mainline @ elstow and joinging marston vale just east of stewartby.
no need for an additional big radius cuvre at the bletchley end.

Diversionary split from MML to EWR happening somwhere just a fraction south of elstow roundabout and joining the present marston vale in between kempston and stewartby.A lot of land seems to be ex quarry, so a diveunder should be doable as long as drainage permits.

This was already looked at. Answer: difficult and expensive.

St Johns linkage should not be used, at least not for passenger diagrams.It might be worth retaining as a freight passing loop.

Why not?

 

[richieb1971]

Try 2tph in each direction between Oxford and Milton Keynes Central plus an aspiration for at least 1tph to/from Aylesbury.

And you are, I believe, proposing that services also run between Bedford and Milton Keynes Central.

Really rather tight on a single line of this length.

Whereas if there is only one train in each direction per hour, that seems a rather expensive bit of infrastructure that isn’t being used for very much.

== Doublepost prevention - post automatically merged: 5 Feb 2022 ==

I would not build a track at all.

In 1978-1979 I watched class 86's and 87's on Bletchley station so frequent that in the southern direction I could still see the back of the past train as the next one came into the station on the same track. Quite a sight. 40 odd years later we are worried about a train every 15 minutes with modern signalling.

I have had my say and still folk can't really tell me why there absolutely must be a connection from Oxford to MKC, where as Cambridge/East can do without. If East can do without and change at Bletchley, then so can Oxford as well.

Completely take MKC out of the equation, because it only unbalances the services between East and West, there isn't any money/space/continguency on the WCML. Bletchley is what 1.5 miles away from MKC? Nuneaton is a major junction and no Avanti trains stop there on a regular basis. The UK doesn't do over taking like I saw in Japan where a 5 minute stop lets a faster train by, something that could easily be accomodated at Bletchley. We are a country that runs by restriction, not inovation.

All a Oxford MKC train is doing is doubling up part of another service that currently runs today. All for the benefit of that little change that nobody wants to do, but its ok for Eastern, but absolutely not for Western folk.

Its just a big nonsense.

 

[Roast Veg]

I have had my say and still folk can't really tell me why there absolutely must be a connection from Oxford to MKC, where as Cambridge/East can do without. If East can do without and change at Bletchley, then so can Oxford as well.

Upthread it has been made clear that all modelling has shown predicted passengers from Oxford will vastly outnumber those from the east. In a delightful convenience of history, the flyover is pointing in the right direction to service that expected demand.

Completely take MKC out of the equation, because it only unbalances the services between East and West, there isn't any money/space/continguency on the WCML. Bletchley is what 1.5 miles away from MKC? Nuneaton is a major junction and no Avanti trains stop there on a regular basis. The UK doesn't do over taking like I saw in Japan where a 5 minute stop lets a faster train by, something that could easily be accomodated at Bletchley. We are a country that runs by restriction, not inovation.

Innovation invariably comes at cost. When an "innovation" doesn't look good on paper it is often wise to leave it there. You are free to perform an independent review into the matter, but don't be under any illusions that East West Rail and Network Rail haven't done their own.

 

[richieb1971]

Upthread it has been made clear that all modelling has shown predicted passengers from Oxford will vastly outnumber those from the east. In a delightful convenience of history, the flyover is pointing in the right direction to service that expected demand.

But it lands in a minefield of WCML traffic.

 

[Bald Rick]

In 1978-1979 I watched class 86's and 87's on Bletchley station so frequent that in the southern direction I could still see the back of the past train as the next one came into the station on the same track. Quite a sight. 40 odd years later we are worried about a train every 15 minutes with modern signalling.

Why do you think it’s every 15 minutes?