Increase tolerances for cornering G force?

[Jozhua]

Hi,
I was wondering wether it is possible, practical or helpful to increase G-force tolerances for passenger rail services.

Most cornering forces are a fraction of that you get on say a bus, coach or even a plane.

The obvious answer is that passengers stand and move about on a train, but in my experience, the sudden jolts have a much larger impact on this than the G-forces involved in cornering. Plus, buses are always heavily accelerating, braking and cornering with standing passengers. Maybe it is worth studying in more detail, with adjustments in the speed corners come on, etc justifying how much lateral G force can be exerted on passengers.

Considering we are ditching tilting stock on a number of routes, and that HS2/3 will not reach as far north as some Northern/Scottish cities, would this be a useful consideration?

 

[4F89]

For what purpose? Increasing cant and speed will increase maintenance costs

 

[Jozhua]

For what purpose? Increasing cant and speed will increase maintenance costs

I was thinking of the ability to increase cornering speed without increasing cant too much, so essentially allowing for a somewhat higher threshold.

 

[4F89]

But that would put more lateral stress on the track, leading to higher maintenance levels

 

[Bald Rick]

Hi,
I was wondering wether it is possible, practical or helpful to increase G-force tolerances for passenger rail services.

Most cornering forces are a fraction of that you get on say a bus, coach or even a plane.

The obvious answer is that passengers stand and move about on a train, but in my experience, the sudden jolts have a much larger impact on this than the G-forces involved in cornering. Plus, buses are always heavily accelerating, braking and cornering with standing passengers. Maybe it is worth studying in more detail, with adjustments in the speed corners come on, etc justifying how much lateral G force can be exerted on passengers.

Considering we are ditching tilting stock on a number of routes, and that HS2/3 will not reach as far north as some Northern/Scottish cities, would this be a useful consideration?

This is already done. Take a train from Newcastle to Edinburgh, or Newbury to Taunton, and you’ll have cant deficiency of 6 deg (150mm) rather than the normal 4.5 deg (110mm).

Above 6 deg, things start flying off tables - laptops, hot drinks, etc etc.

 

[Bletchleyite]

For what purpose? Increasing cant and speed will increase maintenance costs

To allow non-tilt (HS2) stock to run at 125 on the WCML, for one?

 

[Shimbleshanks]

Several decades ago, I read a comment in Modern Railways (probably by Alan Williams but can't be sure) that trains in Norway seemed to have much higher speeds on bends than in the UK, which meant a faster, but less comfortable ride. No idea if that's actually true though.

 

[Bald Rick]

Several decades ago, I read a comment in Modern Railways (probably by Alan Williams but can't be sure) that trains in Norway seemed to have much higher speeds on bends than in the UK, which meant a faster, but less comfortable ride. No idea if that's actually true though.

It’s all physics. I don’t think any railway routinely operates with cant deficiency of more than the exceptional value of 150mm that we do here. Some apply that more widely -the French certainly do.

Going from normal maximum of 4.5deg to exceptional values of 6deg is worth 5-10 mph depending on specific circumstances. Normally 5.

 

[eMeS]

... and if a train comes to a halt on such a curve, do drinks slide on to the floor?

 

[Ianno87]

... and if a train comes to a halt on such a curve, do drinks slide on to the floor?

Best experience of that is stopping in the Up Fast platform at Wolverton!

 

[E27007]

Prior to the WCML upgrade, Railtrack tamped the track for greater cant deficiencies , the curves were then more noticeable to passengers, far from making complaints, passengers were convinced the trains were travelling faster and the timetable had been speeded up, except it had not!
Some find thrill from the "sport" of fast travel.

 

[Bletchleyite]

Several decades ago, I read a comment in Modern Railways (probably by Alan Williams but can't be sure) that trains in Norway seemed to have much higher speeds on bends than in the UK, which meant a faster, but less comfortable ride. No idea if that's actually true though.

I certainly always had the feeling that DB did, but it seems that was just an impression.

 

[eMeS]

Best experience of that is stopping in the Up Fast platform at Wolverton!

Hmmm, quite rare I'd expect.
What happens on the Down Fast platform now seems such a rare event that the station announcements ignore what's happening on it.

 

[Bald Rick]

Prior to the WCML upgrade, Railtrack tamped the track for greater cant deficiencies , the curves were then more noticeable to passengers, far from making complaints, passengers were convinced the trains were travelling faster and the timetable had been speeded up, except it had not!
Some enjoy the "sport" of fast travel.

Is that right? If so why was it done? Reduce low rail wear?

 

[Wilts Wanderer]

Cant deficiency is an important tool for controlling rolling contact fatigue in curves, as part of a regime that also includes rail grinding and gauge-face lubrication. Whilst increasing cant deficiency allows higher speeds, it also increases sidewear which reduces rail life and therefore increases maintenance costs in the medium-long term. The risk at this point is that it would encourage engineers to look for more resilient rail (I.e. limit sidewear through harder rail - such as mill-heat hardened steel) to reduce their costs, but such rail is then more susceptible to internal cracking that doesn’t show on the surface. Without frequent excellent ultrasonic measurements, this can lead to uncontrolled crack growth internally, and you end up with another Hatfield.

== Doublepost prevention - post automatically merged: 30 Sep 2020 ==

Also - don‘t confuse cant and cant deficiency. Cant is the physical superelevation of the outer rail. Cant deficiency is the amount that the rail is not lifted beneath the equilibrium value at linespeed, in order to generate some lateral force which is desirable as explained above. This also allows for the fact that not all trains travel at linespeed, and cant surplus combined with heavy unsprung weight or high yaw stiffness (such as freight vehicles) can cause its own problems. (Edit - to add - this is why freight trains on very high speed lines such as HS1 is a dubious choice, as the curves are canted for 186mph and the freight will only run up to 90mph and is therefore almost permanently curving in cant surplus.)

 

[Bald Rick]

Edit - to add - this is why freight trains on very high speed lines such as HS1 is a dubious choice, as the curves are canted for 186mph and the freight will only run up to 90mph and is therefore almost permanently curving in cant surplus.)

Indeed, and HS1 has a compromised geometry with non ideal can’t as a result.

 

[LNW-GW Joint]

Indeed, and HS1 has a compromised geometry with non ideal can’t as a result.

Love the autocorrect...

 

[Bald Rick]

Love the autocorrect...

I’ve going to leave that. It does it every time! Could have been worse...

 

[Wilts Wanderer]

I had fun with my post as well! First world problems

== Doublepost prevention - post automatically merged: 30 Sep 2020 ==

Indeed, and HS1 has a compromised geometry with non ideal can’t as a result.

Out of interest was this in any way a factor in the early reputation the Class 380 Javelins got for poor ride stability at 140mph?

 

[Bald Rick]

I had fun with my post as well! First world problems

== Doublepost prevention - post automatically merged: 30 Sep 2020 ==



Out of interest was this in any way a factor in the early reputation the Class 380 Javelins got for poor ride stability at 140mph?

Not sure, but I don’t think so.

 

[Ben Bow]

To allow non-tilt (HS2) stock to run at 125 on the WCML, for one?

Don't TPE's class 397 EMU's run at 125 without tilt?

 

[Bald Rick]

Don't TPE's class 397 EMU's run at 125 without tilt?

Nope

 

[brad465]

Don't TPE's class 397 EMU's run at 125 without tilt?

My understanding is that this on the basis they can accelerate faster than previous non-tilting stock like 350s and therefore can travel at 125mph in places where that's not got too much curvature but it's not worth it for other stock to reach that speed, but I'm guessing most prolific curves will see their speed no better than already in place.

 

[Bald Rick]

My understanding is that this on the basis they can accelerate faster than previous non-tilting stock like 350s and therefore can travel at 125mph in places where that's not got too much curvature but it's not worth it for other stock to reach that speed, but I'm guessing most prolific curves will see their speed no better than already in place.

There is no non-tilt speed above 110mph anywhere on the WCML proper.

 

[brad465]

There is no non-tilt speed above 110mph anywhere on the WCML proper.

Yes I probably should have said rather than "can at 125mph in places", were "being tested to see if they could travel at 125mph in places". This was something I read in a RAIL edition a while back, which was proposed but not confirmed.

 

[Senex]

It’s all physics. I don’t think any railway routinely operates with cant deficiency of more than the exceptional value of 150mm that we do here. Some apply that more widely -the French certainly do.

Going from normal maximum of 4.5deg to exceptional values of 6deg is worth 5-10 mph depending on specific circumstances. Normally 5.

The French certainly allow more actual cant than we do (except on the LGVs), but do they allow more deficiency too?

IIRC the new rules came in in the middle of the 1980s and the Midland from London to Leicester was one of the first lines to benefit. The Wigston Curve went up from 70 to 80, so getting the maximum benefit you mention, and that's when the curve on the bridge at Great Bowden went up to 85.

I certainly always had the feeling that DB did, but it seems that was just an impression.

I think DB have been 150 + 150 (cant + deficiency) for many years. It was certainly that back in the 1970s.

In this country, isn't there actual cant of significantly more than 150 mm on the curves between Hele and Cullompton?

 

[Bald Rick]

The French certainly allow more actual cant than we do (except on the LGVs), but do they allow more deficiency too?

If my experience on the infamous ‘snow train’ Calais - Bourg St Maurice is anything to go by, then yes! Pretty hard to keep vertical in the Disco coach, and that definitely wasnt related to the crate of Stella bought on the ferry.

 

[Wilts Wanderer]

In this country, isn't there actual cant of significantly more than 150 mm on the curves between Hele and Cullompton?

I know when the linespeed was increased to 100mph they were the curves with the highest cant deficiency in the UK, and you don’t half feel it at full speed, on the edge of alarming if you’ve got a rough riding set.

 

[edwin_m]

There is no non-tilt speed above 110mph anywhere on the WCML proper.

This is because nobody has really wanted to run a non-tilt train above 110mph until recently, and Virgin wasn't going to give a leg up to a potential competitor so they were only interested in increasing the speed for tilting trains.

There are several fairly straight sections of the WCML, such as either side of Preston and around Lockerbie, where the geometry ought to allow a higher speed without tilt. I believe there's a project going on to investigate this further - it would also reduce journey times for future HS2 services.

 

[LNW-GW Joint]

Yes I probably should have said rather than "can at 125mph in places", were "being tested to see if they could travel at 125mph in places". This was something I read in a RAIL edition a while back, which was proposed but not confirmed.

In the current franchise hiatus, TPE is hardly in a position to spend money to go faster than 110mph on the northern WCML.
397s could run at 125mph on the ECML or GWML if desired (and cleared for the route).
Whether passengers would enjoy the rough ride at that speed is another story.
Avanti wants to run its 80x units at higher speeds on the southern WCML, but that is a couple of years away at the least, and the franchise position is equally vague.