Rail cross sections

[superkev]

I'm not sure what rail is used in the US compared with here but I note the new emd F125 4700bhp 125mph 4 axle passenger loco has an axle loading of around 32tonnes. This is considerably more than our 67s which are looked on as heavy for a bo bo.
K

 

[ComUtoR]

I have no idea what you said but "rail cross sections" ? Do you mean the structure and composition of the rail itself or the railhead design ?

Freight over here tends to be restricted to lower line speeds (we have differential speeds at some locations) and they are "non bogied" and have little to no suspension, relative to passenger stock.

We do have dedicated freight lines which may differ to passenger lines so I'm interested in your query. A little more clarification would go a long way. I'll grab some popcorn and read along when the much much more knowledgable guys come along. Soon™

 

[Harbornite]

I'm not sure what rail is used in the US compared with here but I note the new emd F125 4700bhp 125mph 4 axle passenger loco has an axle loading of around 32tonnes. This is considerably more than our 67s which are looked on as heavy for a bo bo.
K

What are you trying to ask? What is the maximum axle loading of rails in the UK?

 

[jopsuk]

I think he's asking what the difference is between tracks in the US that can happily take a loco that heavy (though no 125mph line has ordered them yet!) and tracks in the UK that even at low speed would crumple under the sheer mass of these beasts. There's very little track in the US is rated for above 100mph; most of it is on the electrified North East Corridor (that has a section with a 160mph limit). There's nothing with a 100mph+ linespeed west of Indiana. All the higher speed track is, as faras I know, Amtrak owned rather than (as with most of the network) freight railway owned

 

[superkev]

I think I was asking if the us infrastructure particularly the track is significantly stronger than the UK/eu or do they have different rules. Is the us rail thickness significantly more?
Not sure but the 32tonnes axle loaded f125 must be by far the heaviest 125mph loco in the world. I hope the motors are not axle hung .
K

 

[DesireToFire]

According to wikipedia https://en.wikipedia.org/wiki/Track_(rail_transport) the heaviest rails in the UK are 60 kg/m and in the US 77 kg/m.

 

[edwin_m]

The contact area between the wheel and the rail is another issue at this sort of axleload. There is a small amount of deformation of both at the point of contact, which makes it a few millimetres across instead of being infinitely small if wheel and rail were absolutely rigid. Up to a certain point steel deforms elastically so will just spring back into shape when the wheel moves on. However if the forces are too great it will undergo permanent (plastic) deformation and over time the rail (and possibly the wheel too) will lose its profile.

This problem doesn't depend on the weight of the rail but it does depend on the wheel diameter and the exact shape of both the wheel and the rail at the point of contract. It's one reason why train wheels can't be smaller than they are.

I don't know whether American wheels and rails are shaped to increase the size of the contact patch and therefore reduce stresses. According to Wikipedia and various random Googles the F125 has 40" wheels, the same as the GE Genesis which has a maximum of 110mph and also a 32 tonne axle load. The older F40PH, also used by Amtrak, also has 40" wheels for 110mph and a weight of 130 tonnes (so 32.5 tonnes axle load if evenly distributed).

It may be that the F125 would cause track damage if used routinely at its maximum speed on standard track.

 

[superkev]

For interest/ comparison UK class 67 125mph has 39" wheels and the class 68 100 or 110mph has 43" (Wikipedia).
K

 

[edwin_m]

For interest/ comparison UK class 67 125mph has 39" wheels and the class 68 100 or 110mph has 43" (Wikipedia).
K

Interesting. Their axle loads would be a lot less than 35t as well.

 

[furnessvale]

Interesting. Their axle loads would be a lot less than 35t as well.

Yes. US class 1 railroads tend to be much more heavily engineered in every respect than ours.

To carry the heavier axle load, the rail section is heavier and deeper.

Sleeper spacing is closer, spreading the load and reducing the effective span of the rail between sleepers.

In one respect their standards are much slacker than ours.

Unless things have changed, I remember years ago as a junior per way engineer, reading of AAR track standards. One thing stood out,

"Gauge for 110mph running. Permitted tolerance 4' 8" to 4' 9"......!!!!!!

 

[edwin_m]

Another quick google for the axle load of the Acela, which as far as I know is the only train in the States that actually does 125mph. It is 23t or 25t according to different sources, so considerably less than the American locos above but quite a bit more than a TGV at 17t. The extra weight is probably due to American trains being built to much higher structural strength standards.

Acela also has 40 inch wheels, compared to about 36" for TGV.

 

[bnsf734]

The maximum permitted weight for a US 4 axle freight car is 286000 pounds which equates to 129.72 metric tonnes so the maximum axle load is 32.43 tonnes.

 

[ac6000cw]

furnessvale and bnsf734 have summed up the US situation well.

The US also makes extensive use of 'rail anchors' (to resist the rails sliding longitudinally through the fasteners) in situations where high tractive efforts/brake forces are common, like on steep gradients. A modern US six-axle freight loco can generate more than twice the low-speed tractive effort of a Class 66... Put two of those on the front of 10,000 tonnes of train and you can start to see why the rails might try to slide, as the train growls it's way up the hill at 10 mph, sanders on and in 'wheelcreep' (controlled wheelslip) mode, helpfully grinding away the railhead as it goes... It's all about hauling freight as economically as possible.

Basically pretty much everything on US railways is bigger and heavier than anything in Europe. Maximum freight train speeds are similar to ours - 50-60 mph for heavy-haul, 70 mph for intermodal (but containers are commonly carried double-stacked in articulated sets of 'well' cars - effectively two 40 foot containers carried per 2 axles, so about double the axle load of intermodal in the UK).

32-33 tonnes is fast becoming the normal freight loco axle load in the US as well - making a 6-axle loco 196 tonnes.

On the other side of the 'track quality' coin, the track standards on branch lines and 'shortlines' can be pretty bad - the lowest Federal track standard is '10 mph excepted', which you could (tongue in cheek) translate into 'hopefully things won't fall off the track too often...'

As for the sanity of 125 mph passenger locos with 32 tonne axle loads - personally I have my doubts...

 

[furnessvale]

Yes. US class 1 railroads tend to be much more heavily engineered in every respect than ours.

To carry the heavier axle load, the rail section is heavier and deeper.

Sleeper spacing is closer, spreading the load and reducing the effective span of the rail between sleepers.

In one respect their standards are much slacker than ours.

Unless things have changed, I remember years ago as a junior per way engineer, reading of AAR track standards. One thing stood out,

"Gauge for 110mph running. Permitted tolerance 4' 8" to 4' 9"......!!!!!!

I appear to have been overprescriptive in my allowance for US track standards.

The link below shows various standards which sound horrendous, eg gauge 4' 8" to 4' 9.5",
superelevation up to 8".

http://utu.org/worksite/PDFs/safetylawsummary/TrackStandards.pdf

 

[ac6000cw]

The Federal track standards are here - http://www.ecfr.gov/cgi-bin/retriev...2f&mc=true&r=PART&n=pt49.4.213#se49.4.213_153

 

[Trog]

The US also makes extensive use of 'rail anchors' (to resist the rails sliding longitudinally through the fasteners) in situations where high tractive efforts/brake forces are common, like on steep gradients.

The use of rail anchors in his country has tended to die out as we moved to high toe load rail clips that would hold the rail in place without them. Is the US use of rail anchors more a reaction to poor quality even if heavy duty track?

 

[furnessvale]

The use of rail anchors in his country has tended to die out as we moved to high toe load rail clips that would hold the rail in place without them. Is the US use of rail anchors more a reaction to poor quality even if heavy duty track?

I tend to agree.

Fit and forget high toe load fastenings are beginning to make inroads in US railroads but the once ubiquitous plain spike is still common, and is very poor at giving a toe load, hence the need for anchors.

 

[XDM]

The Federal track standards are here - http://www.ecfr.gov/cgi-bin/retriev...2f&mc=true&r=PART&n=pt49.4.213#se49.4.213_153

This is fascinating,thanks for the link. Do we have such prescriptive rules,down to specifying the detailed experience & training of pway staff? Or do we leave it to the good judgement of our rail civil engineers? I haven't considered it deeply but I think I prefer the later. The US rules seem a mixture of stalinistic dictat & lawyer led edict.
But maybe we can't trust individual engineers to do the right thing by their professional judgement. However I would trust the few senior rail civil engineers I know to get it right.

 

[Trog]

Interesting that they can have as few as 18 sleepers in 60'-0" in their top category of line, when in this country we would have a minimum of 24 in a siding. By contrast a top grade British mainline would normally be laid at 30 sleepers in 60'-0".

 

[ac6000cw]

I tend to agree.

Fit and forget high toe load fastenings are beginning to make inroads in US railroads but the once ubiquitous plain spike is still common, and is very poor at giving a toe load, hence the need for anchors.

There is quite a lot of CWR on concrete sleepers - presumably using whatever is/was the favoured rail fastening at the time - on high-tonnage mainlines in the US (and 'high tonnage' can easily be more than 200,000 tonnes per day, at high axle loads - even an empty coal/grain/oil train can weigh more than 3000 tonnes).

I'd agree that traditional track spikes seem a poor fixing method by modern standards, but doubtless it's long familiarity and inertia that has kept them in use to this day (a bit like our use of bullhead rail for many years, when everyone else used flat-bottom rail).

It's the differences in railway practices and philosophy that make other countries' railways interesting...

 

[Ploughman]

We do have our own version of spikes in fairly common use until a few years back.
Almost impossible to lift out a full panel of track and have all sleepers still attached to the rails.

 

[Trog]

We do have our own version of spikes in fairly common use until a few years back.
Almost impossible to lift out a full panel of track and have all sleepers still attached to the rails.

Do you remember how when measuring up for a relay the fibron tape always ended up under an elastic spike especially when a train came and it was time to stand out.

 

[Ploughman]

Do you remember how when measuring up for a relay the fibron tape always ended up under an elastic spike especially when a train came and it was time to stand out.

Or worse "Stringing Wire" for a Hallade survey

 

[Trog]

As we had some DC track we used to use strong fishing line to do Hallade, mine got into too much of a state on site once and I had to buy more line. Have you ever tried explaining Hallade and why you need such a strong mono filament line fifty miles from the sea to the owner of a fishing tackle shop. The things we did for BR.

 

[Ploughman]

Or even buying a fishing reel big enough to take 60 metres of wire and not be bothered about the lack of rod connectors.

 

[ac6000cw]

Or worse "Stringing Wire" for a Hallade survey

Not being a track person, I assume the 'Hallade' in question is this one - https://en.wikipedia.org/wiki/Hallade_method ?

 

[Trog]

http://www.iainellis.com/hallade.pdf

A bit more detail on how it works here.

Almost all the maths involved was simple addition and subtraction which in the days before calculators and office computers when this all had to be done by hand was just as well.

 

[ac6000cw]

This is fascinating,thanks for the link. Do we have such prescriptive rules,down to specifying the detailed experience & training of pway staff? Or do we leave it to the good judgement of our rail civil engineers? I haven't considered it deeply but I think I prefer the later. The US rules seem a mixture of stalinistic dictat & lawyer led edict.
But maybe we can't trust individual engineers to do the right thing by their professional judgement. However I would trust the few senior rail civil engineers I know to get it right.

Relative to the 'prescriptive rules' in the US, you have to remember that most of the US rail system is (and always has been) in the hands of vertically-integrated private railroad companies.

Before the 'merger mania' that started in the 1960s (largely in response to financial problems caused by government freight rate regulation, large crew sizes and truck competition), there were a sizeable nummber of railroads that competed for traffic over similar routes. So to stop unscrupulous managements indulging in potentially unsafe maintenance and operating practices to cut costs, you need to have legally enforcable minimum standards - they help keep both a competitive 'level playing field' and employees safe.

One of the earliest pieces of US Federal safety legislation was the 'Railroad Safety Appliance Act' in 1893, designed to cut the toll of deaths and injuries amongst railroad workers, particularly amongst the 'brakemen' who used to run along the tops of freight cars to apply and release handbrakes while the train was in motion. It made continuous brakes and automatic couplers compulsory on all railroads engaged in 'Interstate Commerce' i.e. vehicles/trains that crossed state boundaries - which was effectively all of the 'common carrier' railroads. I think that established the principle that the Federal government had a role to play in railroad safety standards and monitoring - it's just steadily expanded over the years since.

(Note we still don't have a standard automatic freight coupler in Europe, and it was only relatively recently - late 1980's ? - that non-fully brake fitted freights were finally banished from UK rails. US enthusiasts tend to shake heads in disbelief that we still use coupling hooks and side buffers here...).

 

[Ploughman]

If you were a really unlucky Senior Tech Officer / Site Engineer you got sent on a 2 week course in Derby to learn the ins and outs of Hallade.

If you were even more unlucky you found that your hotel had recently featured on Ramsey's Kitchen Nightmares.

and it had got worse.