A coal train passes through my town at least once per day. This train is made up of hundreds of identical hopper cars. When I have been caught at a crossing waiting on the train to go by, I while away the time trying to read the markings on the side of the cars. One marking is “GROSS WT 123456” Another marking is “LT WT 123456”. I assume that these are the empty weight and maximum payload for the car.
What interests me is that these weights vary widely while the cars themselves appear identical. Sometimes the weights vary by tens of thousands of pounds (?). Why would the weights be so different in cars that otherwise seem identical?
Over the weekend, I took a trip on an Amtrak train. I noticed the same phenomenon when we would pass by strings of tank cars or other seemingly identical rail cars. Why aren’t the weights on cars standardized? What makes them vary so wildly?
From this cite the LT must stand for long ton which is the British ton (2240 lbs). It’s a factor of 1.12 so that corresponds to the chart on that page.
I don’t think you’re looking at a tare weight but rather a weight of what the car is rated to carry on the track. Could be wrong. Look forward to a RR person.
Even though they are the same type of cars, they might be rated differently due to age or be from different manufacturers, some may have been upgraded with newer couplers, wheels, draft gear, braking equipment. Or they might be owned by different companies that rate their equipment differently for reasons of their own. Educated guesses only, but it’s most likely for one of these reasons.
SS
Presumably, it costs more to engineer a car to carry a greater weight.
Railroad cars are typically a standard capacity. Given that, the laden weight of the car will depend on what the cargo is. While you could engineer all cars to carry their full capacity of the densest possible carglo that would result in most cars being signficantly over-engineered for the loads they are actually carrying, which would be financially wasteful. So you want a mix of cars constructed to a variety of specifications which reflects the mix of cargos you expect your line to be carrying.
LD LMT (load limit) is the maximum weight of lading that can be carried by the car, to the nearest 100 pounds. This is determined by subtracting the weight of the car when empty from the total allowable gross weight given the size of the car’s journal bearings. The load limit for a car is usually a bit greater than its capacity; the two figures can be equal, but capacity can never exceed load limit.
LT WT (light, or empty, weight) is the weight of the car when empty.
Accompanying the light weight marking is a date indicating when the railroad or owner last verified the car’s weight. The letters for this mark are not always reporting marks; sometimes a location code is used. NEW and a date indicates that the weight shown is the car’s as-built weight, and that it hasn’t been field-checked since.
Just to add to that, most standard 4-axle freight cars on North American railroads can be 286,000 lbs loaded. They weigh the cars before they put them into service to get the LT WT number, and then subtract that from 286,000 to get the LD LMT number. They also re-weigh them after any major repairs and update the LT WT number. Usually if you see a string of newish cars with sequential serial numbers, they weight and load information will be pretty close, but a lot can happen during the hard life of a freight car.
Thanks for the link to Trains Magazine. I should have looked there.
So, what can happen to freight car in the course of its life that would cause its weights to change? The train that I am most familiar with is one that brings coal from Wyoming to a power plant in Texas. All of the cars have the same owner (the power company) and appear to be of similar vintage. Doesn’t the widely varying weights make it more challenging for the coal mine to load the train?
Whole lot of welding going on. Patches, gussets, new panels that have to overlap to the undamaged material by minimum distances. That’s a lot of additional steel added to the empty weight. Getting 10s of thousand tons of coal/rock dumped into and out of in the course of a few years takes its toll. As mentioned above - new gear, rebuilds can change the weight.
The coal loading point probably loads a reasonable margin below the all up max weight to account for car differences.
My guess would be that when the rail cars are designed, the capacity is determined by how long you expect it to last. In other words, a new car might be able to carry 20 tons, but what they really need is for it to be able to carry 10 tons but last 20 years. So the extra capacity when new is just “service factor” for life expectancy. As long as the weight capacity exceeds the amount they’re actually loading, everything is fine. I doubt that loads are custom figured for each individual car.
However, even if they were, it wouldn’t be that tough to handle. As the empty cars are being loaded, they’re actually moving across a platform that I’m sure is just a giant scale (think load cells) and a computer is controlling the loading mechanism. Get a vision system to read the capacity as the car approaches the loading platform and pass that to the computer controlling the loading.
I work for a place that sells such vision systems. They can do everything from verifying printed labels to checking for errors in carpet patterns. Reading numerals is a piece of cake.