Most all American genaral scervice freight cars have 2 sets of 2 axel trucks underneath them. Why is that? Some Brittish carrages have 2 sets of 1 axel trucks. Is this because american cars are hevier than the carrages across the pond? Does it have something with the curve radius? Wouldn’t it be easier for American cars to have 2 sets of 1 axel trucks? I mean, less to maintatin right?
Thanks,
Justin
First, your picture is of a special load depressed center car, not typical of railroad cars. However, your premise of heaviness is correct. North American railroads do have a heaver loading guage, thus larger and heavier cars, thus two two axel trucks.
Justin - just a little before your time (by about a decade) was the rude experiment with the TTOX single bogie skeleton flatcars…Gawd did I hate those switch pickin’, frog hoppin’ nightmares that seemed to be in the middle of about every switching derailment they called me on. (Carl, are there any left? …I never wanted to see those empty in the middle of a moving freight train.)
As close as you get to a single bogie truck anymore are the roadrailers…
As for 3-axle cars, there are still a few of the DODX 100+ ton flatcars still out there plus others.
Plenty of span bolstered trucks out there too, like the schnabbel cars (pictured) and large tank cars (“bombs”)
Justin’s photo of the HD load capacity “low center carrier” is an excercise of {RR equipment} beauty. That arrangement has so many pivot points to enable it to follow almost any RR curve…
I count 14 points of pivot to allow it to follow curvatures.
All of the roadrailers I’ve handled use 2-axle trucks. (the roadrailer people call the whole wheel set assembly a bogie)
Justin,
I don’t have a lot of time now, but you might want to zip over to the MODEL RAILROADER forum and see if any of the old timers can point you in the direction of a story from the late sixties about the history of freight car trucks in North America. I was a teenager then and I found it fascinating. Like Joni Mitchell says “you don’t know what you’ve got until it’s gone”, but I really wish I could better remember the variety of trucks I could still see in the early sixties at Irricana, AB. It took railroads a long time to come to the standard type (or two?) we see today.
AgentKid
This might be an easier way to find the information you were looking for.
http://www.trains.com/trn/default.aspx?c=a&id=210
AgentKid
Axle loads in Europe are very low, most cars can barely haul more than a road haul truck.
American railcars are upto 150 ton, with axle loads of 38 tons, nearly 20 tons more than a allowable axle load in Europe.
The 4 axle freight cars are gaining popularity in Europe too but won’t weigh more than 80 to 90 tons.
Justin, if you can find a copy of George Hilton’s book “American Narrow Gauge Railroads”, it has a very good section on narrow gauge rolling stock evolution from 4 wheel to 8 wheel cars. American standard gauge rolling stock also seemed to evolve in a similar manner in its early years. Part of the early problem was that American railroad track (at that time) tended to be rougher and had more curves than our English counterparts. Four wheel cars just don’t track as well as two truck, 8 wheel cars do under those circumstances. This was one of the reasons that English built 0-4-0 steam engines were not a big success in America at the beginning of our railroad history. Rough track and sharp curves led to the development of the 4-wheel pilot truck and four equalized drive wheels that defined the popular 4-4-0 locomotive. Admittedly, a 4 wheel locomotive has a different set of dynamics than a four wheel freight car, but some of the same problems do affect both. Nowdays, our axle loadings rule out 4 wheel cars for any application I can think of, and an 8 wheel car has the added advantages of riding smoother and tracking better than a 4 wheel car. At any rate, see if you can borrow a copy of Hilton’s book from the library, I highly recommend it. You might also do some reading on early steam locomotive development.
Justin - The reasons Britain stuck to 4-wheelers until quite recently are complicated, but certainly part of it was to do with curve radii on sidings. Much of Britain is very densely built up, and due to pressure of space many old factories, collieries, docks etc. had sidings with extremely tight curvatures. To serve these, British freight cars (‘goods wagon’) stayed extremely small – most wagons built up until the early 1960s had a 10’ rigid wheelbase. The air-braked standard types introduced the late 1960s (previously most British wagons were vacuum braked or unfitted) still only had 4-wheeled chassis of 18’ to 21’ or so, and even this was too large for some customers’ sidings – Ministry of Defence traffic still required a dedicated fleet of 10-footers in the early ‘90s . Also, some industrial track was lightly laid – colliery branches for example were often unable to take heavy locomotives or cars. Closure of these old sidings due to the decline of old industries and the collapse of the UK wagonload business means that large bogie wagons are now prevalent, though there are still plenty of 4-wheelers about.
Certainly a small, simple 4-wheeler is cheaper to build and maintain than a large car, but obviously you need more of them to carry the same load, which ends up costing more overall. Also 4-wheelers can have undesirable ride characteristics, as a result of which they usually have a relatively low speed limit, even on good track.
As others mentioned, having a pair of trucks helps greatly on rough track, perhaps more critical for frontier railroading. Single axles transmit any irregularities directly to the carbody, as I found riding a fairly modern DMU in Britain some years ago. Over here, cross-overs would jerk the Turbotrain enough that it was recommended that passengers remain seated in station terminal approaches. In both cases, light weight also contributed to the roughness.
One of the controlling factors in car capacity is bearing capacity. This can be increased by increasing the size of the bearing (axle diameter or width) or by increasing the number of bearings. One of the reasons for having additional axles on heavy-duty flatcars, like the one you pictured, is bearing capacity for the ultra-heavy loads. The other is axle loading on the railroad structure itself.
North America, because it went to 4-axle freight cars very early, based its practice on large capacity cars. For small shipments the local wayfreight would usually carry an LCL (less-than-carload) boxcar and small shipments would be loaded/unloaded at various stations. This business was quite labor intensive, since shipments would get exchanged between cars at major terminals to be forwarded on towards their ultimate destination. The railroads here conceded the “retail” freight business to trucks a long time ago.
In Britain small shipments would match the small cars rather better. The small cars had other advantages. It was not uncommon to have very short turntables (barely long enough to fit the wheelbase of the wagon) on a siding. Cars could be turned 90 degrees and pushed immediately into the industry or warehouse. This saves an incredible amount of space in a country where space is at a premium, and the same procedure could occur inside the building. Manpower was quite adequate to push the cars. As in North America, though, the small shipments were very
According to the ORER, the car in the picture, KRL 16450, is actually just a depressed center flatcar (FD), not a Schnabel (LS).
Amazingly, the October 2007 ORER does list 274 of the TTOX cars. Perhaps they keep them around as bad examples.
.
Eric, I’m a little surprised at that–I haven’t seen any of those single-axle cars in years! I don’t have an ORER that recent, but should get one soon–maybe on CD ROM. My 7/06 issue shows close to 500 of them.
You know, I’ve heard about the lightweight passenger cars (think Aerotrain) and how rough they rode, and I can remember at least three attempts to revive the concept for freight equipment (a lightweight box car in the 1960s, a four-section articulated auto rack in the 70s, and those TTFX and TTOX cars in the 80s or thereabouts). Each time they thought they hadn’t made the mistakes of the previous attempts, but they just weren’t any better.
The big tank cars (anything with more than a pair of four-wheel trucks) are rapidly becoming museum pieces or scrap fodder these days. There are still quite a few DODX flats with three-axle trucks, and the KRL and QTTX fleets of heavy-duty flat cars were expanding, at least until the economy turned sour.
Here’s a question for somebody who has a better understanding of physics than I. I’ve seen heavy-duty flat cars with pairs of six-wheel trucks at each end, and with three four-wheel trucks at each end. I would assume that, with wheels and bearings of the same size, both types would have the same gross rail load. What would be the advantages of one over the other–economy for the six-wheel trucks (think about how they’d be attached to the carbody) and curvability for the added four-wheel trucks?
Yes, Roadrailers these days ride on four-wheel bogies, no longer on single axles that are permanently attached to the trailers.
Mudchicken,
It is indeed a common knowledge that those front-runner cars were a PITA. I wonder though, why were they in use for so long, why was there not a trial in one particular corridor to make sure these cars will indeed work? So much money wasted on those derailments cleanup!
Rode talgos in Spain over the same routes with both two single axels on each car and a two axel boggie between cars. The two axel 4 wheel boggie rode much better IMHO. That was the time I converted from the idea of single axel cars for the US system.
Can someone describe how a car with three four-wheel trucks at each end would be suspended…? Where would the pivot points be…?
Would one truck be located with a pivot pin…and the other two be suspended with a frame across them {pivot in center}, and each truck pivoted from that frame…?
{Actually, thinking about that last thought…don’t think that would work either}
Much like a car with two trucks would be, Quentin–one center pin per end, span bolster connecting one truck with another span bolster connecting the other two.
The Talgo’s don’t really even have single axles, each wheel is in a half axle.
The Axle does not continue under the car.
Don’t forget some of the stack platforms, or five packs (five platform sets), share two axel trucks, too. It is therefor: platform one and five have one and a half trucks each while the other three platforms share each truck inbetween so that there may be only 6 trucks instead of 10…