Explanation: The higher the net to tare ratio, the more revenue cargo a car can carry relative to the light weight.
Bottom line - the 286k standard for four axle cars will remain the standard, and only an adoption of the three axle bogie will result in a greater load factor capability.
I am trying to figure why an empty 315K car weighs more than a 286K car when both are basically the same car. The figures look bogus to me. The light weights of the cars will be just about the same. The AAR wants the 315K cars and so this is how it will be.
What makes the net/tare of a car with 3 axle trucks higher?
3 axle trucks are cool, they have been used before but railways seem to eventualy drift away from them again. Passenger coaches once used them extensively and large tank cars the 70’s, some coal cars too.
But instead of 3 axle trucks and/or 315K cars how about using shorter regular cars. If you can squeeze 286K into a 40 foot length car type, a train load will carry more weight then 60 foot 315K cars for the same length of train effectively resulting in a greater load factor capacity without changing the truck designs or the rigidity of 3 axle trucks.
Modern center flow hoppers seem to do this to some extent compared to older covered hopper designs due to improved design and shape without going outside the loading gage.
You could even go to even shorter rigid 2 axle cars with no trucks. Three 40 ton 2 axle cars could equal one 120 ton 6 axle car on 3 axle bogies. The simplicity of the short 2 axle car might have a higher net / tare ratio.
I also realy don’t understand why new locomotives mostly use 3 axle trucks, when 2 axle trucks are more flexable and can handle higher speeds. The economies of scale changes all the time.
Three-axle trucks on freight cars will never become much more than oddities because of the additional complexity of their design and maintenance compared to the three-piece two-axle truck, which is about as simple and straightforward as you can get.
Additional weight (315K) is possible, but it requires larger wheels, heavier rail and more ROW maintenance. The last point is probably the real reason that 315K cars won’t become more common.
C-C trucks are more common on locomotives to allow for the additional weight required for better low-speed tractive effort. See other postings for more information on this issue.
The marketplace is going to determine what becomes “standard”. The open access cheapskates are certainly not going to pay for maintenance; That’s somebody else’s responsibility and it would eat into their expected transportation savings.[}:)]
CSSH: Alan Zarembeski (Sp?) would be glad to see you caught on .
125 ton trucks use larger wheels, journals, etc, so naturally they’d weigh more. According to the ZETA-TECH guys, the 315k’s cause more wear and tear per revenue ton than 286k’s.
The net/tare of 3 axle trucks would be higher because you have more axles to support the weight. A 286k car has four axles with 71,500 load limits. By throwing in two extra axles at the 71,500 per axle limit, we now have a car with a gross load limit of 429k. Subtracting the extra tare from the addition of the two extra axles would still give us a car with revenue load limit in the high 300ks.
And who paid them how many bucks to come up with the incredibly complex calculation of the net to tare ratio of 286’s vs 315’s? Do they have a math genius on their staff?
Alan has quite a bit of alphabet soup after his name, including PhD and PE…You can’t get through a railroad technical paper w/o finding him somewhere in the footnotes.
Would not be surprised at all if this was an AAR or FRA commissioned study.
Here is the obvious deal. For a 14.5 ton increase in gross weight, 10 tons of additional product can be carried in each car. That additional weight could ge a little less than a 5% increase in revenue per car IF, (very big if) rates for the larger cars were not dropped. On the cost side, there comes increases for the purchase price of the larger cars and money for track upgrades and higher costs for track maintanence. There might be some slim reductions in operating expenses.
On the whole, it might not be a good deal for the railroads, but the point is moot. If the market place wants it, competition among the railroads will cause it to come about.
Sure add ten tons to an existing car to make it capable to haul 14 tons. But build a new car design from scratch and you might get a way better ratio, especialy if someone wants to. That net / tare ratio can easily be changed by technological improvements, of course even the 3 axle truck can be improved so we will see. But you can’t realy say “never”.
3 axle trucks are still a way to reduce axle load and still haul heavy loads. So is using four 2 axle trucks. But Like I said, just build the cars shorter with the same carrying weight capacity and you should improve net / tare using standard components. This will work for bulk comodities. Shorter cars are lighter, long cars need heavier frames.
A 14.5 ton increase in gross weight to gain 10 tons in product carried means a 4.5 ton increase in car (tare) weight. Three-axle trucks will reduce the axle load but the track still has to carry the extra weight. Note that loaded ore jennies aren’t that much heavier on a per car basis but their short (24’) length concentrates the weight, resulting in the need for a heavier track structure.
It will be interesting to see if larger cars pan out. If it is cheaper it will happen. That is why people using covered hoppers like rail-it is cheaper.
About 1978, while I was still working for the C&NW, FMC obtained some new covered hoppers capable of loading 125 tons of soda ash vs. the then standard of 100 tons. The UP came up with new rates based on the the standard cost sharing formula spliting the savings 50/50 with the customer.
Once the cars started to operate we discovered some bad assumptions. On the C&NW it was no problem to move the car from the UP at Council Bluffs/Fremont to Proviso(Chicago) connections but when we checked into spotting a car at glass plants we served we found we could not make it into the plant. Few reciever’s sidings could not safley handle the added weight.
Although the C&NW did not set the benchmark for track maintance even the UP was having problems on their mainline. The excess wear showed up rapidly on the mainline between the soda ash mines, which are just west of Green River, and the Green River yard. After a year the UP agreed to let FMC keep the lower rates but dropped the minimum weight back to 100 tons.
However, with time and I am told improvements in rail, covered hoppers carrying 125 tons of soda ash became the standard. 315k cars may or may not become the standard but never say never.
even the UP was having problems on their mainline. The excess wear showed up rapidly on the mainline between the soda ash mines, which are just west of Green River, and the Green River yard. After a year the UP agreed to let FMC keep the lower rates but dropped the minimum weight back to 100 tons.