Are Top Speeds Really Just the Recommended Speed?

[Railperf]

The original class 86 bogies exert too much force on track joints to be used regularly over 100mph. That's why the examples authorised to do 110mph have flexicoil bogies.
Class 67 diesel locos were originally designed for 125mph operation but were initially limited to 110mph to stay within track force limits. The class later achieved a derogation to run at 125mph despite the slightly higher track forces at that speed.

 

[Far north 37]

I wasn't meaning the 87mph value specifically, the class 90 and 87 had higher 110mph speeds and the 92 seems quite low in comparison given it's a powerful engine. I assume the trade off is it's much better for freight although I always think of 92's in passenger service as my only experience with them is on the sleeper.

The class 92 was designed initially for freight and overnight sleeper services it was never intended to run at high speeds.

 

[Railperf]

Class 91 is another example of a locomotive designed to run safely at 140mph but is limited to 125mph in normal service. The reason being that UK railway authorities insist in-cab signalling is needed for speeds over 125mph, and government refused to to spend money on it. In addition to this, the class is limited to 110mph when leading blunt end first for aerodynamic reasons.

 

[Cherry_Picker]

Not sure old oak common drivers would ever have been passed on voyagers would they.

Yes they were, back when Virgin were running the XC franchise .

 

[gimmea50anyday]

Yes drivers were based at old oak as the stock was serviced there and services ran into and out of Paddington. A throwback to intercity days where 47, 50, and HSTs could have worked both XC and GW services. Corresponding Train Managers and catering crew were of course and still are based at Reading

 

[43096]

East Midland HST's timings are based on 110mph running for instance.

They’re not. When linespeed on the Midland was increased to 125mph a few years ago, timings were tightened and required faster running to achieve them. They might show as 110mph timings in the data feed, but the reality is different.

 

[hexagon789]

I assume the trade off is it's much better for freight although I always think of 92's in passenger service as my only experience with them is on the sleeper.

The sleepers are timed for 80mph for comfort anyway, so the 87mph top speed doesn't present much of a problem ordinarily, especially with a 92's prodigious acceleration.

 

[hexagon789]

Class 91 is another example of a locomotive designed to run safely at 140mph

The BR design specification was for 150mph/240km/h:

 

[Railperf]

They’re not. When linespeed on the Midland was increased to 125mph a few years ago, timings were tightened and required faster running to achieve them. They might show as 110mph timings in the data feed, but the reality is different.

Yes..i agree ..in reality they more often than not run faster than 110mph on the 110mph+ sections of track. But i am still sure that the sectional running times are based on 110mph..but for some reason seem to require greater than 110mph to achieve them.

 

[Railperf]

Class 91's reached 162mph - less than the 165mph that would have been required as 10% overspeed testing for regular 150mph operation in service.

 

[hexagon789]

Class 91's reached 162mph - less than the 165mph that would have been required as 10% overspeed testing for regular 150mph operation in service.

I simply meant they were specified for 150mph, not that BR seems to have ever planned for that in service.

 

[hooverboy]

Taking this example of a Class 90 loco, I am sure it could do quicker than the top speed. If so, why is the top speed rated at that value?

The HSTs (for example) can do quicker than 125mph, despite a lot of speed restrictions at this limit. Is the 125mph just the operating top speed recommended by the manufacturer? I mean, have a flat line and open the throttle and I'm certain an HST would go faster.

So if an HST went on the HS1 route, why can't it go quicker than 125mph?

I may be confusing two different approaches here, as I guess there will be infrastructure restrictions, compared with trains that physically cannot do quicker than the quoted top speed.

general rule of thumb is "top speed" is top speed in regular service.

in reality proper to speed is about 10% above, to cater for speedo error,wheel wear,environment etc etc.
so your common or garden 150/156 sprinter will be quite capable of running at 85mph with a good engine,good rails,a fresh set of tyres and a fair wind behind it.

 

[Ianno87]

Yes..i agree ..in reality they more often than not run faster than 110mph on the 110mph+ sections of track. But i am still sure that the sectional running times are based on 110mph..but for some reason seem to require greater than 110mph to achieve them.

Point to point SRTs are variously rounded up and down section-to-section. So some individual point to point times will work out as greater than 110mph just because that section was rounded down the nearest half minute, not up.

The overall end to end sequence of SRTs should average out to 110mph (or just below) based on the total of all the successive SRTs.

 

[trainmania100]

I have clocked 132mph according the the TMS on voyagers between Didcot and Reading. OOC drivers wanting to get home on late shifts no doubt...

Are there no overspeed grids that apply the brakes on overspeed.?

 

[hexagon789]

Are there no overspeed grids that apply the brakes on overspeed.?

TPWS overspeed grids are only fitted in advance of some severe reductions in permissible speed. Though Virgin's Super Voyagers have TASS which I think would prevent such an overspeed.

I am slightly surprised that Voyagers don't have a speed limiter fitted like HSTs and some DMUs such as 170s.

 

[TheEdge]

Are there no overspeed grids that apply the brakes on overspeed.?

As hexagon789 says TPWS overspeed loops are not everywhere, the vast majority are at stop signals protecting conflict points or on approach to big speed reductions. They also tend to be set fairly high, as in a train would have to be going very very fast to actually set them off, especially normal speed limit overspeeds, they tend to be 30+mph higher then their relevant speed restrictions and well within the area where a train under decent control would be braking.

 

[trainmania100]

As hexagon789 says TPWS overspeed loops are not everywhere, the vast majority are at stop signals protecting conflict points or on approach to big speed reductions. They also tend to be set fairly high, as in a train would have to be going very very fast to actually set them off, especially normal speed limit overspeeds, they tend to be 30+mph higher then their relevant speed restrictions and well within the area where a train under decent control would be braking.

Okay thanks for letting me know I guess drivers would know where they are then as they gradually notice their locations, so they'd know where to go over the speed limit to make up time

 

[hexagon789]

They also tend to be set fairly high, as in a train would have to be going very very fast to actually set them off, especially normal speed limit overspeeds, they tend to be 30+mph higher then their relevant speed restrictions and well within the area where a train under decent control would be braking.

That seems surprisingly high but presumably still within safe limits.

It seems to me that really that in a lot of instances there is nothing to prevent overspeed, other than the potential for it to be caught in an OTDR download.

 

[Bald Rick]

Some units had maximum speed limits they could rarely reach in service. 4-VEPs for example were rated at 90mph, which (apparently) they could reach only with the assistance of gravity and a following wind.

 

[hexagon789]

Some units had maximum speed limits they could rarely reach in service. 4-VEPs for example were rated at 90mph, which (apparently) they could reach only with the assistance of gravity and a following wind.

I believe most of the slam-door Mk1 third-rail units bar the "Greyhounds" and 4REPs balanced at about 88 mph on level track.

When a many of these units were introduced in the '50s and '60s the Southern Region 'officially' had an 85mph ceiling anyway.

 

[AM9]

I believe most of the slam-door Mk1 third-rail units bar the "Greyhounds" and 4REPs balanced at about 88 mph on level track.

When a many of these units were introduced in the '50s and '60s the Southern Region 'officially' had an 85mph ceiling anyway.

The class 309s were rated at 100mph and regularly achieved that on level track between Chelmsford and Colchester.

 

[hexagon789]

The class 309s were rated at 100mph and regularly achieved that on level track between Chelmsford and Colchester.

I know, I did say 3rd rail units

 

[TheEdge]

That seems surprisingly high but presumably still within safe limits.

It seems to me that really that in a lot of instances there is nothing to prevent overspeed, other than the potential for it to be caught in an OTDR download.

They do seem high in some locations but as you say they are well within the safe limits.

Massive overspeeds can be spotted in other ways, I think the GOTCHA detectors can spot it for example and a few other systems out there. But no, for normal non cab signalled stock, there is often nothing else. The other thing that may show it up to a signaller or controller paying attention would be significant early running.

 

[Metal_gee_man]

It still amazes me that many of the EMUs with connecting corridors run in the south manage 100mph with the brick like front ends and distinct lack of aerodynamics when they were built! I've heard of drivers needing to wrap up to keep warm and stuff rags around the door to stop the cab turning into a fridge! I guess many of them were tractioned to do 110-120 mph but i can't imagine many drivers wanting to do those speeds, they regularly only reach 90 mph on 100 mph stretches of track as it is

 

[noddingdonkey]

The 90s are more than capable of 125mph. They would need disc brakes however. Tread brakes would be too expensive to maintain and a fire risk with regular 125mph use.

If that were the case, wouldn't a few examples have been converted for when deputising for 91s by now?

 

[TRAX]

It still amazes me that many of the EMUs with connecting corridors run in the south manage 100mph with the brick like front ends and distinct lack of aerodynamics when they were built! I've heard of drivers needing to wrap up to keep warm and stuff rags around the door to stop the cab turning into a fridge! I guess many of them were tractioned to do 110-120 mph but i can't imagine many drivers wanting to do those speeds, they regularly only reach 90 mph on 100 mph stretches of track as it is

Some 350s and 387s do 110.
Not sure about the wrapping up and rag stuff though.

 

[Jamesrob637]

Given 350s now do 110 in regular service (quite thrilling on a fast Euston to MK!) would they have been tested at up to, or near enough, 125?

 

[Journeyman]

It's worth bearing in mind that in the past most trains could be pushed to go well beyond their design speed, with a bit of "encouragement" - like 9Fs hitting 90mph, which must have been a sight (and sound!) to behold. However, most modern trains now have some form of speed limiting built into them that makes it very hard to exceed design speed.

 

[AM9]

I know, I did say 3rd rail units

Ah yes, my mistake. However the traction hardware was virtually the same in respect of 4x282hp DC motors (class 309) vs 4x275hp DC motors (some SR units had those instead of 250hp), and the 309s were carrying more weight. At the time I beleive the fast lines 3rd rail DC supply wasn't as heavily loaded as now.

 

[AM9]

Given 350s now do 110 in regular service (quite thrilling on a fast Euston to MK!) would they have been tested at up to, or near enough, 125?

Wasn't the class 350 uplift due to a modification by Siemens to allow greater motor spinning speeds so would have been design approved before release on service duties?