Exeter St Davids to Exeter Central "bank" capacity constraints

[Dan G]

I think I read here that the bank between St Davids and Central in Exeter is limited to 5tph each way. That seems quite low to me. What are the capacity constraints between the two?

 

[yorkie]

That was, at least partially, answered in the following post:

Between Exeter St David’s and Exeter Central the ruling gradient is 1:36 and consequently trains in both directions may not be stopped on the gradient by signals. Similarly while a train is signalled down into Exeter St Davids, there are restrictions on other movements at the far end of platforms 1-3.

However someone may have something more to add to that...

 

[zwk500]

I think I read here that the bank between St Davids and Central in Exeter is limited to 5tph each way. That seems quite low to me. What are the capacity constraints between the two?

The steep gradient is compounded by the very low speed of the curve at St Davids. However 5tph would require a 12-minute interval between times, and the runtime between the two stations is 3-5 minutes. I don't know what the headway is down there but I'm willing to bet it isn't as long as 7-9 minutes.

 

[Halish Railway]

The steep gradient is compounded by the very low speed of the curve at St Davids. However 5tph would require a 12-minute interval between times, and the runtime between the two stations is 3-5 minutes. I don't know what the headway is down there but I'm willing to bet it isn't as long as 7-9 minutes.

I’m guessing that rounding up to 12 minutes is for performance slack (IIRC 3/5 trains going from St David’s to Central originate from beyond Exeter).

 

[Snow1964]

I travelled that way in the 1980s, and on one occasion got off at Central and train must have stopped on the bank towards St David's awaiting for a platform. The back coach was still in Central platform so platform staff had to hover to stop people running for it. I think it was a 50 +11 or 12 mk2s

Perhaps signal outside St David's got moved when they replaced the semaphores, and anyway there is no longer any slam door stock, but maybe that's why they didn't like trains stopping on the bank, because back of longer trains were still in Central platform so tempting to jump on.

 

[30907]

I’m guessing that rounding up to 12 minutes is for performance slack (IIRC 3/5 trains going from St David’s to Central originate from beyond Exeter).

Yes. You need to allow for extended stops at St Davids to reverse direction (2tph), to empty the train before shunting to sidings (1tph), or to get a path northwards (2tph). The present 5tph may not equal capacity, but it won't be far short either IMO.

 

[83G/84D]

You have to take platform occupancy at St David's into consideration for service frequency. Trains from Exeter Central towards Paignton and / or Barnstaple are quite often overtime in Platform 1 or 3 waiting paths due to late running class 1 trains on the main line. Just yesterday I was there watching a Paignton bound service in platform 3 waiting for around 10-15 minutes two successive down services to leave ahead of it. Both were next stop Newton Abbot whilst the Paignton stops most or all stations.

 

[testertrev]

You cannot signal a train from E312 at Exeter Central down the bank unless E335 is cleared into platform 1 or 3 .

 

[Watershed]

The planning headway between Exeter Central and St Davids is 3 minutes. However, the platform reoccupation at Exeter Central is 4 minutes, and the minimum dwell time there is 1.5 minutes. If successive trains use the Up Waterloo (rather than one using the Up and the next the Down, or vice versa), the second train cannot depart St Davids until 2 minutes after the first train has departed Central. The sectional running time from St Davids to Central is 2.5 minutes for most traction types.

When combined, these factors limit the practical headway to 5.5 minutes in the Down direction and 6 minutes in the Up direction. That would suggest a maximum of 10tph - but that still ignores platforming at St Davids. Given that most services from Central either terminate or reverse at St Davids, and only 2 platforms can be accessed at St Davids from the Central direction, the realistic capacity of the Central-St Davids line is likely to be closer to 5tph each way, as originally suggested. You could only run 10tph if all trains continued beyond St Davids, e.g. to/from Tiverton or Barnstaple, or went into the sidings after a short dwell.

 

[Wilts Wanderer]

The reality is that May 23 timetable is approaching full practical capacity with the existing service patterns when all operational needs (dwells, pathing, reversals, empty/secure train etc) are taken into account.

 

[Dan G]

Not simple then! Thank you all

At the risk of breaking my wafer-thin understanding, does this mean there is or isn't room for 2tph towards/from Honiton, leaving aside the necessity of a new loop out that way to enable such a service?

 

[30907]

Not simple then! Thank you all

At the risk of breaking my wafer-thin understanding, does this mean there is or isn't room for 2tph towards/from Honiton, leaving aside the necessity of a new loop out that way to enable such a service?

You can extend the Central terminators - which is IIRC Devon's plan.
I suspect you could squeeze a 6th tph up and down the bank - if not, Central still has a bay