TTOX and other two axle car designs

[Anonymous]

I hope some of you can clear this up for me. I have been researching the use of modern two axle car designs such as the TTOX skeletal flats, and it seems well documented that these designs have inherent tare weight advantages over the standard four axle/two bogey cars, e.g. the TTOX were roughly 5,000 lbs per platform lighter in tare weight than the articulated spine cars of similar platform length. To summarize, the reasons I have found so far as to why these cars (specifically the TTOX) have been taken out of service is:

(1)The rigid wheelbase design causes problems with track curvature,
(2)The TTOX has a load limit of 65,000 lbs, too light for modern heavy trailer weights,
(3)The light weight of the cars (25,000 lbs) can cause problems if an empty TTOX car was placed near the front of a train with a heavy trailing load,
(4)The TTOX cannot handle trailers over 48', a problem since most trailers today are 53'
(5)????

With these points in mind, why wouldn't it be prudent to do the following:
(1) Replace the 28" wheels (with an axle load limit of 55,000 [?] lbs) with 36" wheels with an axle load limit of 71,000 lbs, along with a beefed up suspension. This would allow load limits of up to 112,000 lbs per platform, qualifying the cars to handle the 129,000 GVW trailers.
(2) Add radial steering to the single axle bogeys to allow better curving characteristics
(3) Extend the platforms roughly 2' on each end to accomodate the 53' trailers
(4) With the modifications listed in (1), (2), and (3) above, the light weight should increase to 30,000 lbs, decreasing the pull over tendancy when an empty TTOX+ is placed at the front of a consist, while still being roughly 5,000 lbs per platform lighter than a corresponding articulated spine car with 53' platforms.

With a 5,000 lbs per platform weight savings, an 8,000' long train of TTOX+ cars would weigh approximately 360 tons less than a corresponding train of articulated spine cars (assuming the same relative load weights). For a time sensitive TOFC train, I would think this weight savings would have a significant impact on fuel consumption. Any thoughts?

[TH&B]

Here's what I think. (5) they do not use enough standard parts, articulated spine cars have close to the same weight tare but use standard trucks (and less slack too). Roadrailers moved to standard trucks also after trying something special. Standard parts are important if you ever need to be serviced at flatwheel jct.
Also radial steering single axle bogies are fancy but standard two axle trucks can take alot of uneven twisty track too, not just curves.

[TH&B]

Here's what I think. (5) they do not use enough standard parts, articulated spine cars have close to the same weight tare but use standard trucks (and less slack too). Roadrailers moved to standard trucks also after trying something special. Standard parts are important if you ever need to be serviced at flatwheel jct.
Also radial steering single axle bogies are fancy but standard two axle trucks can take alot of uneven twisty track too, not just curves.

[rrnut282]

Single axle radial steering would make it even more of a *** step-child as far as maintaining (see flatwheel jct above). Why engineer something more complicated when an existing 2-axle truck will provide superior tracking and capacity? I don't think the weight savings in fuel consumption will ever outweigh the liabilities of scarce parts and possible derailment.

[M636C]

leftlimp,

I think the problems indicated by the previous posts indicate why these cars are no longer regarded as a practical proposition.

There were two distinct suspension designs for these cars, one using cast pedestals with relatively conventional coil springs (which could be upgraded fairly easily) but the other was based on British designs, and used special tapered leaf springs (known in England as the "taperlite" design). This was analagous to the springs used on Chevrolet Corvette cars (but not made from carbon fibre). I think I only ever saw one of the "taperlite" equipped cars in service. It would be costly to design new springs for these cars.

I would think that these cars would be less likely to be derailed by train forces than a standard 89 foot flat car, owing to their short length. The single axle designs may be more likely to derail due to poor track conditions.

It would probably be regarded as uneconomic to lengthen these cars for 53 foot trailers.

Peter

[dharmon]

As Pooh would say...

TTOX TTOX for now.....

sorry couldn't help myself...

[Anonymous]

Thanks for the insights! I thought it might be a question of non-standardized parts for the suspensions and radial steering. Two reasons I am interested in these cars is 1) I read where TTX is modifying some older 48' platform spine cars into 53' platform cars, and thought if they could justify the costs of that, they could take a look at doing similar modifications to the lower tare TTOX cars (assuming they haven't all been scrapped), and 2)Swedish railcar maker K Industrier AB just came out with a two unit paper hauling car (called the Hiqqrrs-vw011) which has the rigid single axles on each unit, so the idea of saving tare weight by using single axles isn't anethema in Europe. Here's the link for anyone interested:

www.kindustrier.se/Products/Freight/index.htm

Regards

[TH&B]

Single axle instead of trucks in principal is not a bad idea at all, but it realy doesn't belong in North America. Track should be built fot two axle cars wich it has always been in Europe. One example is when there is jointed rail in Europe the joints are direct across from each other, this gives good ride quality for 2 axle cars. Even though we use welded rail on most mains, yards and sidings are still bolted. Two axle cars ride very poorly on American bolted rail because it's not flexible enough. Anyways paper is heavy so why put it in 2 axle cars when a 4 axle will take twice as much?

[Hugh Jampton]

QUOTE: Originally posted by 440cuin

Even though we use welded rail on most mains, yards and sidings are still bolted. Two axle cars ride very poorly on American bolted rail because it's not flexible enough.

It makes no difference in yards and sidings because the speeds are low.

The track joint is a discontinuity in the rail , and the 2nd Moment of Inertia (the bendyness) is much lower at a track joint, typically between 10 and 40 times more depending on the rail and fishplate sections. So the flexibility of the joint is actually greater.
The biggest problem with 2 axle vehicles is the high curving forces which lead to high wheel wear rates. Typically around 0.8mm/100km compared with 0.2mm/1000km for a 4 axle vehicle in the UK, based on some research that I did a couple of years ago. The curving forces are proportional to the length of the vehicle, which is why european 2 axle vehicles are usually quite short

[TH&B]

I ment the 2 axle car is too stiff, I didn't mean the rail, I don't know if flexability of the rail helps. Even at slow speed the two axle car will come right off the rail, the American style truck is extremely flexable on very uneven and curved track. Take a look at the spur tracks at a paper mill for example, see how "wiggely" the rails are. One of the problems with the American railways buying "off the shelf" European roling stock is it's too stiff and plops right off the rail, that's why it's rarely done if at all in freight.
American jointed rail is completely different from European jointed rail.

[Supermicha]

Here we have the old problem, that we can´t compare railroads in europe and america. You have high car loads, they are not possible with two axle cars. Modern two axle cars in germany can run 160 km/h, thats very much for a fright trains.

Micha

[Anonymous]

Another example of the use of a single axle bogey is the Trough Train, which employs a single axle bogey on each end of the consist.

That being said, remember the TTOX cars are light haul cars. TOFC/spine cars do kind of go against the grain of the usual heavy haul railcars prefered by U.S. railroads. So in this vein, the single axle concept has a substantial merit for such light haul type cars.

Also, remember that radial steering is not limited to single axle bogeys. Both GE and EMD locomotives provide the option of radial steering arms on their three axle trucks, and the RailRunner bimodal technology utilizes radial steering on its two axle bogeys. Such options reduce the angle of attack, reducing rail and wheel wear.

[kenneo]

These cars are a menace. They simply won't stay on the track. If the single axel truck (two axel car) is so good, why are the European railroads not purchasing any - and haven't for a good number of years?

Prior to the Civil War, the US railroads had abandoned this design because it could not carry a decent load and stay on the track. So, the smart folks designed the two axel truck and the four axel car. Cars stayed on the rail and decent loads could be carried. Oh, and by the way, they rode more comfortably for passenger cars.

When we had an earlier thread on 6-axel cars it was mentioned that the only reason that 6-wheel (3-axel) trucks were used on passenger cars was RIDE QUALITY. I have ridden single axel (truck) cars, two axel trucks and 3 axel trucks under passenger cars. The TALGO, for instance, between Portland and Seattle, uses a single axel articulated truck between each car. And do you ever know where each joint and frog are!! You hear it, and the car takes a lurch that can throw you down. With a standard truck configuration, you may feel it and probably hear it. 6-axel cars? Won't feel it and probably won't hear it, either.

Two axel cars are unstable. Period. No mater what kind of track they are running on.

[Anonymous]

When they were still being used, I recall the BNSF trains using the 80-85 degree crossovers of Metra in Joliet. The 2 axles were unstable compared to the others crossing the diamond. Don't know if this led to any freight damage or not. But, it appeared it could be possible from the rougher ride on the 2 axles. Jerry

[Anonymous]

If the TTOX cars had been modified with radial steering arms, would this have made any difference in the cars' performance?

[kenneo]

QUOTE: Originally posted by leftlimp

If the TTOX cars had been modified with radial steering arms, would this have made any difference in the cars' performance?

No.

Problem has to do with basic physics.

Radial steering would have had little to no effect.

[Anonymous]

Regarding impacts when riding over joints/frogs, that is probably a problem that a beefed up suspension would take care of, probably need some type of air suspension to supplement. (What type of suspension does the Talgo use?) Radial steering would take care of the angle of attack problem on curvature.

[Anonymous]

BTW, does Ed King have an opinion on this subject?

[kenneo]

QUOTE: Originally posted by leftlimp

Regarding impacts when riding over joints/frogs, that is probably a problem that a beefed up suspension would take care of, probably need some type of air suspension to supplement. (What type of suspension does the Talgo use?) Radial steering would take care of the angle of attack problem on curvature.

All of the jimcracks and whizzbangs - tilting, radial steering, multirate springs, and so on. Problem is, there is just one axel. When it drops down, EVERYTHING drops down with it. With multiple axels, the truck frame drops down, not EVERYTHING. In a curve, a single axel car, when the flang contacts the rail head, jerk to turn. With multiple axels, the truck frame does the jerking and the car starts to turn slower instead of going from straight ahead to turning rate all at once.

The chunnel cars are "standard construction" in that they have two trucks of two axels each. On that run, you don't feel the switches and don't hear them. You can't tell if you're in a turn unless you are going though it at its design speed. Single axel cars simply would not work here.

[Anonymous]

Eric,

Good explanation.

[Anonymous]

After some research, I found that one of the main reasons that single axle trucks bear a greater impact at rail joints than two axle trucks is the rail compression factor. As the wheel passes over a rail, it presses down on it, and as the joint is approached the next rail section will be slightly higher than the occupied rail, thus there is a THUMP when the joint is crossed over. One way to ameliorate this affect for single axle trucks is to use larger diameter wheels, which will "soften" the angle of the wheel/joint contact. The TTOX used 28" wheels, so if those were replaced with 38" wheels, this affect would be lessened. The question is if it would be enough to make a significant difference.

Dave

[oltmannd]

The real killer was getting squeezed off the rails when there was high trailing tonnage. Even with added weight, it would remain a problem because of the geometry. Intermodal train tonnage is much higher now than in the late 70s when these cars appeared, so that makes the problem worse.

[broncoman]

Has anyone seen any of the other classes of 2 axle spine cars. The TTX website shows only the TTOX class, but I thought there were others. I haven't seen one in about 5 years now. I thought they had all been removed from service. I had thought about posting a have you seen any of these cars post earlier but this seem as good a place as any to ask!

Thanks

[TH&B]

Keep in mind the larger wheels will add weight and raise the centre of gravity. If the track was smooth enough the 2 axle car would be ok, but the whole idea of trucks is that you can use rougher track and still get a good ride. What would be the point in adjusting all of the track at huge expence just to be able to run a few long wheelbase two axle cars that may be marginaly cheaper to build or have less weight?
I do know that in Germany they use two axle cars for freight at 160 to 200 km/h trains but the main track is ultra smooth and yet in yard track and sidings these cars have a bumpy ride, but not an unstable ride because the joints are across from each other. In the US the joints are staggered wich gives a smoother ride for cars on trucks but gives an unstable ride for two axle cars. There is still more bolted rail main line around than you would think.
Have you seen in Germany they use 4 axle trucks (8 axles per car) with 8' wheeels and very low deck height? Again these cars demand very smooth track and even most other European countries can not use this design.

[Anonymous]

I suspect with scrap steel prices as high as they are, they've been or will soon be sent to the srapper.

I don't know of any other two axle cars in the TTX fleet. The TTOX came in two "flavors": The single unit and a drawbar connected "four pack". The only other possible single axle railcar in U.S. freight service today would be the Trough Train (which has single axle trucks on the end units), but I don't know if the Trough Train is currently running anywhere. BTW, the wheel size on the single axle portion of the Trough Train is 38".

Dave

[mudchicken]

From a trackman's perspective:

(1) I do not EVER AGAIN want to deal with these things again in a yard. These suckers (single bogie trucks) are hands-down the worst switch pickers, mechanical switchman and flopover switch hoppers ever seen. They also do strange things around frog guard rails. Any savings generated by the single axle is not given to the track department to pay for the corresponding increase in damages to switch points and switch OTM usually caused by bare table TTOX cars.

(2) Increase tonnage on these things and they aught to be banned from anyplace with jointed rail. Wheel size is NOT going to mitigate the issues of impact damage at a single point. Joint end batter would only rise because of fewer but bigger impact hits.

(3) The concept of steerable/ torsion sprung trucks causes me concern. AAR/TTC in Pueblo ought to be looking at what this does in terms of rail climbing in curves, not on the high rail, but on the low rail with the angle of attack changed. The F.A.S.T. track in Pueblo has done some evaluation work on these cars, but I never heard the outcome.

Agree with Eric/Kenneo that these cars can be a menace in the US....If they do make a comeback, I hope some serious "real world" testing is done prior to introduction into the rail fleet. Really do not want another episode similar to what happened with center plate lubrication on double-stack well cars shortly after their placement into heavy use.


[banghead][banghead][banghead]

[Anonymous]

I agree that there would need to be sufficient testing before a prospective modified (read: "upgraded") version of TTOX ever surfaces. But it sounds like the clinical testing done at Pueblo doesn't always account for real world experiences with new innovations.

From a rail joint damage perspective, how is it that wheels on single axle trucks would cause more joint damage than a similar size wheel on a two axle truck?

BTW, what was the problem with the centerplate lubrication on the double stack well cars to which mudchicken refers?