Scotrail InterCity 125 (HST) units, do they actually run at 125mph?

[Deltic1961]

Just wondered, fastest they run on my local line (Dyce to Aberdeen) is 75mph.... and that's only for probably 3 or 4 miles. Seems such a waste.

 

[43096]

Just wondered, fastest they run on my local line (Dyce to Aberdeen) is 75mph.... and that's only for probably 3 or 4 miles. Seems such a waste.

There's no 125mph authorised lines north of Edinburgh and Glasgow, so no, they don't run at 125mph.

 

[XAM2175]

Just wondered, fastest they run on my local line (Dyce to Aberdeen) is 75mph.... and that's only for probably 3 or 4 miles. Seems such a waste.

The shorter carriage sets aren't permitted to run at 125 mph anyway as they have insufficient brake force. I don't necessarily view it as a waste - yes, they're now working in a role where their full capability isn't required, but it doesn't minimise the fact that in their previous roles that high-speed capability was relied upon for many years.

 

[nottsnurse]

In fairness, for a significant amount of time and a not insignificant amount of mileage, those HST sets operated on the MML were barely stretched.

 

[GC class B1]

The shorter carriage sets aren't permitted to run at 125 mph anyway as they have insufficient brake force. I don't necessarily view it as a waste - yes, they're now working in a role where their full capability isn't required, but it doesn't minimise the fact that in their previous roles that high-speed capability was relied upon for many years.

Are you sure that they are not able to run at 125 MPH. I believe the power cars are braked to the same rate as the trailer cars. I remember when recommissioning tests took place after major overhauls two power cars ran at 125 MPH.

 

[XAM2175]

Are you sure that they are not able to run at 125 MPH. I believe the power cars are braked to the same rate as the trailer cars. I remember when recommissioning tests took place after major overhauls two power cars ran at 125 MPH.

FGW modified their power cars to have a reduced braking force (similar to the original two-stage configuration) as they found that the Castle set power cars were doing a lot more of the braking than the trailers were. The modification evened out the braking levels and thus resolved the problem they were having with brake-block wear on the power cars. ScotRail inherited GW's power cars and to the best of my knowledge haven't undone the modification since there's nowhere they can hit 125 mph anyway.

 

[43096]

FGW modified their power cars to have a reduced braking force (similar to the original two-stage configuration) as they found that the Castle set power cars were doing a lot more of the braking than the trailers were. The modification evened out the braking levels and thus resolved the problem they were having with brake-block wear on the power cars. ScotRail inherited GW's power cars and to the best of my knowledge haven't undone the modification since there's nowhere they can hit 125 mph anyway.

If the ScotRail power cars have the lower brake force and are the same as they were when with Great Western, then the Castle set point is an irrelevance, as the mod must have been done by FGW/GWR pre-Castle introduction.

 

[Bill57p9]

I believe the I7C sets are limited to 100mph. Certainly the timetable is scheduled for max 100. Even then there are few 100mph stretches of track north of the central belt.

 

[Sm5]

No, but the acceleration coming off the forth bridge past EDI airport is seriously impressive.

 

[GC class B1]

FGW modified their power cars to have a reduced braking force (similar to the original two-stage configuration) as they found that the Castle set power cars were doing a lot more of the braking than the trailers were. The modification evened out the braking levels and thus resolved the problem they were having with brake-block wear on the power cars. ScotRail inherited GW's power cars and to the best of my knowledge haven't undone the modification since there's nowhere they can hit 125 mph anyway.

Surely then if the power cars brake at the same rate as the trailer cars, the number of trailer vehicles will not affect the train braking rate. The short formation HSTs will then still be able to run at 125 MPH.

 

[najaB]

FGW modified their power cars to have a reduced braking force (similar to the original two-stage configuration) as they found that the Castle set power cars were doing a lot more of the braking than the trailers were. The modification evened out the braking levels and thus resolved the problem they were having with brake-block wear on the power cars. ScotRail inherited GW's power cars and to the best of my knowledge haven't undone the modification since there's nowhere they can hit 125 mph anyway.

I'm not 100% sure about it, but when they came north weren't they timetabled at 125mph?

 

[hexagon789]

Surely then if the power cars brake at the same rate as the trailer cars, the number of trailer vehicles will not affect the train braking rate. The short formation HSTs will then still be able to run at 125 MPH.

Post original two-stage brake set-up, yes. But as mentioned FGW had its power cars modified to restrict their braking effort as the nature of how the brakes apply on HSTs meant that repeated light applications resulted in excessive brake pad wear on power cars as they were doing most of the initial braking effort.

I haven't read of other TOCs being affected though.

I'm not 100% sure about it, but when they came north weren't they timetabled at 125mph?

Yes, but does that definitely mean they ran at 125mph?

ScotRail's safety case is only for 100mph.

 

[fgwrich]

No, but the acceleration coming off the forth bridge past EDI airport is seriously impressive.

As is on the stretch out of Haymarket heading Westwards. It's certainly 385 rivalling!

 

[Nicholas Lewis]

The shorter carriage sets aren't permitted to run at 125 mph anyway as they have insufficient brake force. I don't necessarily view it as a waste - yes, they're now working in a role where their full capability isn't required, but it doesn't minimise the fact that in their previous roles that high-speed capability was relied upon for many years.

Shame they didn't regear them for 100mph as would have given better acceleration.

 

[hexagon789]

Shame they didn't regear them for 100mph as would have given better acceleration.

I don't think it's necessary for the cost that would've incurred. They take off like greased lightening as it is!

 

[GC class B1]

Post original two-stage brake set-up, yes. But as mentioned FGW had its power cars modified to restrict their braking effort as the nature of how the brakes apply on HSTs meant that repeated light applications resulted in excessive brake pad wear on power cars as they were doing most of the initial braking effort.

I haven't read of other TOCs being affected though.


Yes, but does that definitely mean they ran at 125mph?

ScotRail's safety case is only for 100mph.

My original point still applies. If all vehicles in the train brake at the same rate then the number of vehicles is irrelevant. Short formed trains will stop in the same distance as longer sets so they will all be capable of braking from 125 MPH.

 

[hexagon789]

My original point still applies. If all vehicles in the train brake at the same rate then the number of vehicles is irrelevant. Short formed trains will stop in the same distance as longer sets so they will all be capable of braking from 125 MPH.

Yes, but my point is that this doesn't apply for ex-FGW sets as the power cars do not brake at the same rate as trailers. Not in the same way as the original HST set up with the two-stage brake but enough that GWR restrict 3-car Castle sets to 90mph for instance.

 

[GC class B1]

I understand that the modification to the power car braking only applied to braking steps below Full Service and that the Full Service brake force was not affected. As the Railway Group Standards performance requirements only apply to stopping distances in Full Service, and the modification didn’t reduce these, the max speed of short formed sets should not be affected.

 

[najaB]

Not in the same way as the original HST set up with the two-stage brake but enough that GWR restrict 3-car Castle sets to 90mph for instance.

The fact that an operator limits their stock to a given speed doesn't necessarily mean that the stock cannot travel faster. Perhaps they've limited their sets to 90mph because it's fast enough to deliver the timetable and saves fuel/wear and tear.

 

[43096]

Post original two-stage brake set-up, yes. But as mentioned FGW had its power cars modified to restrict their braking effort as the nature of how the brakes apply on HSTs meant that repeated light applications resulted in excessive brake pad wear on power cars as they were doing most of the initial braking effort.

I haven't read of other TOCs being affected though.

East Midlands ran a 2+4 set at 125mph.

 

[hexagon789]

I understand that the modification to the power car braking only applied to braking steps below Full Service and that the Full Service brake force was not affected. As the Railway Group Standards performance requirements only apply to stopping distances in Full Service, and the modification didn’t reduce these, the max speed of short formed sets should not be affected.

I haven't heard that distinction between braking steps mentioned but that would make much more sense than an outright restriction of brakeforce. I was informed the restriction was to 3 bar max on power cars but presumably that applies below full service then?

It was a former BR brake engineer who explained the original set-up, revised set-up and FGW set-up to me, but he is retired I understand and only had the details of the FGW modification second hand.

The fact that an operator limits their stock to a given speed doesn't necessarily mean that the stock cannot travel faster. Perhaps they've limited their sets to 90mph because it's fast enough to deliver the timetable and saves fuel/wear and tear.

90 for 3 trailers. 0-2 trailers is 75mph, 4 trailers is 100 and 5 125mph according to GWR instructions that a GWR driver of Case sets was good enough to explain on another forum.

 

[XAM2175]

If the ScotRail power cars have the lower brake force and are the same as they were when with Great Western, then the Castle set point is an irrelevance, as the mod must have been done by FGW/GWR pre-Castle introduction.

Yeah the Castle bit shouldn't have crept in there.

 

[GC class B1]

I haven't heard that distinction between braking steps mentioned but that would make much more sense than an outright restriction of brakeforce. I was informed the restriction was to 3 bar max on power cars but presumably that applies below full service then?

It was a former BR brake engineer who explained the original set-up, revised set-up and FGW set-up to me, but he is retired I understand and only had the details of the FGW modification second hand.


90 for 3 trailers. 0-2 trailers is 75mph, 4 trailers is 100 and 5 125mph according to GWR instructions that a GWR driver of Case sets was good enough to explain on another forum.

My information came from the retired InterCity Brake engineer.

There are other reasons for restricting the speed of short formation trains than purely brake performance. For example, fewer vehicles means a brake defect on one vehicle will have a greater effect on the braking performance of the train.

 

[hexagon789]

My information came from the retired InterCity Brake engineer.

So did mine, the gentleman I posed my questions to in relation to a previous thread on a similar subject of HST braking I came across while searching for information via Google. The search at the time turned up some posts on another forum to this one relating to speed restrictions on short-formed HST sets and how that after the brake modifications there was no need to speed restrict sets with fewer than five trailers as the power cars were now full braked throughout the speed range.

I was able to ask him a few questions and I either asked him directly or it came up about the later modifications which FGW made to their sets, the reasons behind it and the result. Part of that was that after those modifications FGW restricted its sets to reduced speeds if their were fewer than 5 trailers. Those speeds were later confirmed by a current driver who signs the Castle sets in relation to short-formed Castle sets being restricted to the speeds I outlined above.

Neither of them mentioned anything beyond the brakeforce being restricted and the engineer proffered 3 bar as the figure but he wasn't sure.

It's possible it's the same gentleman as yourself, but the lack of sureness re the FGW mods suggests not.

East Midlands ran a 2+4 set at 125mph.

Indeed but EMT/EMR aren't FGW

 

[D365]

Just wondered, fastest they run on my local line (Dyce to Aberdeen) is 75mph.... and that's only for probably 3 or 4 miles. Seems such a waste.

In what way is 75/100mph ”a waste”?

 

[hexagon789]

My information came from the retired InterCity Brake engineer.

There are other reasons for restricting the speed of short formation trains than purely brake performance. For example, fewer vehicles means a brake defect on one vehicle will have a greater effect on the braking performance of the train.

In fact i now see that I had overlooked a conversation I had with another member if this forum on this subject. In their reply they do indeed state that the restriction was only to light applications and the 4.1bar full service pressure remained unaffected by the mods.

So, really there is indeed nothing to prevent safe use of a short set at 125, except that defensive driving policies may mean that because of the reduced brakeforce in low brake settings, the need for those speed restrictions comes in because the braking distances could only be met with a full service application?

Could that be the reason for the GWR restrictions?

 

[43096]

Indeed but EMT/EMR aren't FGW

Really, I never knew that!

I was replying to your "I haven't read of other TOCs being affected though.", which confirms that it didn't affect at least one other operator.

 

[GC class B1]

In fact i now see that I had overlooked a conversation I had with another member if this forum on this subject. In their reply they do indeed state that the restriction was only to light applications and the 4.1bar full service pressure remained unaffected by the mods.

So, really there is indeed nothing to prevent safe use of a short set at 125, except that defensive driving policies may mean that because of the reduced brakeforce in low brake settings, the need for those speed restrictions comes in because the braking distances could only be met with a full service application?

Could that be the reason for the GWR restrictions?

I think you are correct. Although drivers understand the different braking performance of the various traction they sign, minimising the effect of different train formations is good practice. Also short form HST sets are unlikely to be operating on routes requiring significant high speed running.

 

[Clansman]

Every 25mph quicker you travel, you save *roughly* 10 seconds per mile.

75mph = 48 seconds per mile
100mph = 36 seconds per mile
125mph = 29 seconds per mile

75mph to 125mph means saving around 20 seconds a mile, which, by the time you factor in the longer acceleration and braking, you end up no better off than when you started on services that stop every 10-20 minutes.

So take a straight set of line, say a classic example like St Madoes to Monorgan (between Perth and Dundee). 90mph throughout, and 10 miles long. If you wanted to increase that to 125mph, which is perfectly doable on that alignment, you'd need to factor in the additional time to accelerate and brake. Given the line-speed transitions, set this at, say, 1 mile such that 125mph is covered across 9 miles.

90mph = 40 seconds per mile = 40 x 10 = 400 seconds
125mph = 29 seconds per mile = 29 x 9 = 260 seconds
----
= ~2.3 mins journey saving time between Perth and Dundee on current timings

Aberdeen to Dyce line max speed stretches (3 miles)...

75mph = 48 seconds per mile = 48 x 3 = 144 seconds
125mph = 29 seconds per mile = 29 x 3 = 86 seconds
----
= ~1 min journey saving time between Aberdeen and Dyce (assuming you could raise all speed limits with a max of 125mph on current 75mph stretches)

The cost to upgrade that infrastructure to 125mph would run into the tens of millions. Whereas you can introduce faster accelerating rolling stock which can off-set at least a minute in the very same journey time without the upgrades, which is exactly what ScotRail have done with short HSTs vice 170s/158s. The same applies to Glasgow to Edinburgh, where a 385 can cover all stops between Waverley and Queen Street in exactly the same time as it would have taken a 170 to run semi-fast with calls at Haymarket, Falkirk High, and Croy.

Moral of the story? Upgrading existing line speeds isn't as promising as it seems for short stretches of diesel lines.

In the example of Dyce to Aberdeen, the best investment that can be made to decrease journey times isn't raising line speeds on existing alignments in most cases. Instead it is by electrifying the lines so that acceleration can off-set line speed upgrades. Ie, a 385 would cover Aberdeen to Dyce slightly quicker than a 4-car HST, at a much lower operational cost. Just like how a HST can cover the same journey quicker than a 170/158, albeit at a much higher operational cost.

 

[Railperf]

I don't think it's necessary for the cost that would've incurred. They take off like greased lightening as it is!

As is on the stretch out of Haymarket heading Westwards. It's certainly 385 rivalling!

The 385's do 0-60mph in around 44 secs compared to around 64 secs for a 2+4 HST. But the 60mph to 90mph time shows the HST's superiority once rolling - 50 seconds vs 60 secs for the 385. I measured 0 to 99mph in around 2.5 mins for both. What's interesting here is the Class 385's superior start gives it around a 20 second advantage from rest to 2.5 miles over the HST. Both limited to 100mph though! One of the issues for the HST is the slow releasing brakes compared to a unit, and the fact drivers can't give them full power from a start.
I'd love to see what the MTU's connected to a modern AC drive would achieve.