GWR 'Castle Class' Maximum Speed

[TimeMooses]

Hi there, after looking at the new Dec 2020 TT on Realtime Trains, I couldn't help but notice that some services are now pathed as 'Castle Class HST' rather than 158/168/170/175. They've also listed it as being 'Planned 110 MPH Max'. From what I've gathered elsewhere the Maximum Speed for these sets was 100 MPH owing to the reduced brake force from fewer trailers etc. Has there been a change to allow them to operate at 110 or is this just a mistake on RTT's part? Thanks!! (Here's a link to one of the relevant services https://www.realtimetrains.co.uk/train/W30908/2021-01-07/detailed)

 

[43096]

Hi there, after looking at the new Dec 2020 TT on Realtime Trains, I couldn't help but notice that some services are now pathed as 'Castle Class HST' rather than 158/168/170/175. They've also listed it as being 'Planned 110 MPH Max'. From what I've gathered elsewhere the Maximum Speed for these sets was 100 MPH owing to the reduced brake force from fewer trailers etc. Has there been a change to allow them to operate at 110 or is this just a mistake on RTT's part? Thanks!! (Here's a link to one of the relevant services https://www.realtimetrains.co.uk/train/W30908/2021-01-07/detailed)

Ah, the old planned data in RTT - this is for planning purposes. It does not necessarily reflect either the engineering performance of the train or, indeed, the type of train used on that service.

HSTs with 4 trailers are not speed restricted. They can be, and have been, operated at 125mph.

 

[John R]

How much 110mph (as opposed to 100mph) cleared track there is between Cardiff and Penzance is a moot point though (and how much of any of that would actually be achievable when you take into account the usual stops for those services).

 

[craigybagel]

How much 110mph (as opposed to 100mph) cleared track there is between Cardiff and Penzance is a moot point though (and how much of any of that would actually be achievable when you take into account the usual stops for those services).

IIRC, parts of the Bristol - Taunton line are 110mph max. That's the only place I can think of greater than 100mph on routes that the Castle HSTs run on.

 

[hexagon789]

Ah, the old planned data in RTT - this is for planning purposes. It does not necessarily reflect either the engineering performance of the train or, indeed, the type of train used on that service.

HSTs with 4 trailers are not speed restricted. They can be, and have been, operated at 125mph.

While post mid-1980s alterations to the HST braking system made this true for HSTs ordinarily. When I mentioned that this meant even two powercars could run safely at 125mph in another thread on this forum relating to the Castle sets I was then informed by another member that the GWR power cars had their brakeforce reduced and so they cannot run at 125 without sufficient trailer cars.

Additionally the Class 255 driving instructions issued to GWR drivers states the following:

As stated in the Class 255 traction manual issued to drivers, the maximum speeds are as follow:


2 Power cars and 4 trailer vehicles - 100 mph
2 Power cars and 3 trailer vehicles - 90 mph
2 Power cars and 2 trailer vehicles - 75 mph

Also, provision is made to run the trains as "loco and coaches" (where the 36-way jumper cable between the rearmost coach and the rear power car disconnected, and the rear power car therefore does not power the train). In such cases the speeds would be:

Power car with 1, 2 or 3 vehicles (with the rear power car counting as one vehicle) - 75 mph where linespeed is 90 mph or above, and 60 mph where linespeed is 85 mph or below.

This does seem to tie in with the idea that GWR power cars have their brakeforce reduced either that or its simply company policy.

 

[supervc-10]

Are there any Castle routes where 125mph operation is possible anyway? I didn't think there was any 125mph running west of Bristol.

Edit: Don't know why this just posted. I'm sure I clicked post hours ago! Ah well.

 

[hexagon789]

Are there any Castle routes where 125mph operation is possible anyway? I didn't think there was any 125mph running west of Bristol.

Edit: Don't know why this just posted. I'm sure I clicked post hours ago! Ah well.

Nothing higher than 110 past Bristol and nothing higher than 100 south of Huntspill LC just south of Highbridge and Burnham which is where the seven-mile long 110mph section ends.

 

[brad465]

How much 110mph (as opposed to 100mph) cleared track there is between Cardiff and Penzance is a moot point though (and how much of any of that would actually be achievable when you take into account the usual stops for those services).

Nothing higher than 110 past Bristol and nothing higher than 100 south of Huntspill LC just south of Highbridge and Burnham which is where the seven-mile long 110mph section ends.

I imagine the 110mph section doesn't make much difference to the journey time overall (even for non-stop trains), however I would have thought a 2+4 HST set would have no trouble getting to that speed despite stopping because of its improved acceleration as a shorter set. The only other time it would get to that speed is on ECS movements that happen to go that way.

 

[hexagon789]

I imagine the 110mph section doesn't make much difference to the journey time overall (even for non-stop trains), however I would have thought a 2+4 HST set would have no trouble getting to that speed despite stopping because of its improved acceleration as a shorter set. The only other time it would get to that speed is on ECS movements that happen to go that way.

No problem at all in reaching 110, given its only 2.5 mins to reach 100 mph, but simply they aren't allowed to do so - 100 is the maximum permitted for the "Castles".

 

[Railperf]

I imagine the 110mph section doesn't make much difference to the journey time overall (even for non-stop trains), however I would have thought a 2+4 HST set would have no trouble getting to that speed despite stopping because of its improved acceleration as a shorter set. The only other time it would get to that speed is on ECS movements that happen to go that way.

Given the distance needed to accelerate from 100 to 110mph and then to either coast or brake back to 100mph - it does hardly seem worth it. The line is so straight for long sections - it is a shame that it isn't a blanket 125mph throughout - but i guess the resignalling costs and probable level crossing closures / replacement with overbridges and underpasses rendered that unviable for the fw non-stop trains using it.
Castle HST's are running mainly stopping services on a timetable that isn't particularly demanding and does not require flat out running at even 100mph never mind 110mph. Plus as good as the short HST's accelerate, their braking is worse than a DMU.
Any truth in the GWR power cars having been modified for lower brake force and why? I'm struggling to comprehend that, as the greater bake force was part of the reason HST's were able to brake from 125mph in the same distance as a 100mph loco hauled train.

 

[brad465]

Given the distance needed to accelerate from 100 to 110mph and then to either coast or brake back to 100mph - it does hardly seem worth it. The line is so straight for long sections - it is a shame that it isn't a blanket 125mph throughout - but i guess the resignalling costs and probable level crossing closures / replacement with overbridges and underpasses rendered that unviable for the fw non-stop trains using it.
Castle HST's are running mainly stopping services on a timetable that isn't particularly demanding and does not require flat out running at even 100mph never mind 110mph. Plus as good as the short HST's accelerate, their braking is worse than a DMU.
Any truth in the GWR power cars having been modified for lower brake force and why? I'm struggling to comprehend that, as the greater bake force was part of the reason HST's were able to brake from 125mph in the same distance as a 100mph loco hauled train.

I travelled on one between Weston-Super-Mare and Taunton earlier this year and recall the set being early by around 1-2 mins on RTT all the way (while sitting in each station until scheduled departure time), which maybe down to a large cushion in timetabling that goes with your statement they don't require flat out running, but still do. I don't how how much the poor braking offsets the higher top speed, as even if HST sets go to 100mph they're still better than the 90mph Turbos or 158s do on those services.

I imagine the 125mph concept on that stretch has been contemplated regularly; as a DTG Train Simulator user I've experimented with driving over the Bristol-Exeter route at 125mph where curvature isn't an issue. If the virtual travel is anything like the real world, I only managed to save about 5-6 mins over the otherwise 30 minute journey from Bristol-Taunton. They might consider it as an aside to a resignalling project if cost and effort is not otherwise worth it.

 

[hexagon789]

Any truth in the GWR power cars having been modified for lower brake force and why? I'm struggling to comprehend that, as the greater bake force was part of the reason HST's were able to brake from 125mph in the same distance as a 100mph loco hauled train.

Worth remembering that with the original braking system which was two-stage, the power cars were under braked at certain speeds and that is why originally short formations were speed restricted. After the brake pads, and on the power cars the mountings were changed, plus the two-stage brake isolated the power cars then in effect braked their own weight throughout the speed range. Though that brakeforce remains at least slightly non-linear, the tread blocks account for 20% of the power car brakeforce so the actual braking is mildly non-linear (though you get a slight bite from the discs at lower speeds anyway but nothing like as pronounced as with cast-iron tread brakes) but importantly it meets the W125 curve so it's not really of consequence.

 

[John R]

I imagine the 125mph concept on that stretch has been contemplated regularly; as a DTG Train Simulator user I've experimented with driving over the Bristol-Exeter route at 125mph where curvature isn't an issue. If the virtual travel is anything like the real world, I only managed to save about 5-6 mins over the otherwise 30 minute journey from Bristol-Taunton. They might consider it as an aside to a resignalling project if cost and effort is not otherwise worth it.

I'm not sure what else you were expecting. You save just over 7 secs a mile at 125 compared with 100, so even 40 miles at the higher speed is 5 mins maximum.