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
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.
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.
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.
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.
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:
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?
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
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.
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.
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.
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.
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
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.