CSX Freight Train

[jason1973tl]

O.K. I know by now we have all heard the commercials. A CSX Freight Train can move tons of freight 436 miles on a gallon of fuel. Someone needs to explain to me how that is possible. Does CSX have alien technology we don't? I am sure if that was actually possible all our cars would run on pixie dust by now. I have yet to figure out how they are pencil whipping the data, but they must be.

[Ryland]

They get a bulk discount.
The rolling resistance of a steel train wheel on a steel train track is pretty low, you are then using a large enough diesel engine that the efficiency of it is most likely up in the 35-45% range (some large ship diesels are 50% efficient), compare that to the 22-24% of a gas car.
You of course have train cars that are not perfect, but they are so close together that each one of them is more or less drafting the one ahead of it in a very controller manner.
Fright trains also go at pretty reasonable speeds, 50mph or so.
I suspect that a semi-truck would have some pretty impressive numbers as well if it was fully loaded and going at an ideal speed.

[RobertSmalls]

Nope, a freight train probably couldn't move more than a few feet on one gallon. Their ridiculous claim of one ton, one gal, 436 mi is based on the factual 436 ton-miles per gallon figure, which requires that you have tens of thousands of tons of freight all going from one point on the rail network to another.

Trains have an advantage over trucks (which are in the 100-200tmpg range) due in part to the very low coefficient of rolling resistance of steel wheels on steel rails. The aerodynamics of trains is also interesting in that each train car is drafting the one in front of it.

Anyway, trains have a lot going for them, but moving one ton of freight 436 miles is something they are terrible at. For that particular task, your best bet is a small pickup truck, or maybe a Jetta or a Prius with a trailer.

[NeilBlanchard]

Diesel electric train locomotives are serial hybrids. So the diesel engines are run a near constant RPM. And the electric traction motors have maximum torque at 0 RPM, and they are much more efficient.

Trucks have to use 17-22 speed transmissions and so they are at their maximum efficiency only a fraction of the time during acceleration.

And yes, trains have lower rolling resistance, and better overall aerodynamics, and economy of scale -- and we should start using them more to move freight.

[Piwoslaw]

A smaller part of the savings is the greater cargo mass to overall mass ratio: A freight train is 1-4 locos and then 40-200 cars. With a very few exceptions, each truck trailer has it's own tractor, with it's own engine, A/C, etc. So if a truck weights 40tons, then the actual cargo is maybe 80% of that weight, while for a 10kton train the cargo is probably closer to 90%-95%. (I'm just guesstimating those numbers, so please correct me if I'm wrong.)

Also, once a truck gets off the highway it has to stop at every intersection, while a train can probably cross the continent withut stopping more than 3-4 times. Neither trucks nor trains have regenerative braking, though.

[jamesqf]

Originally Posted by Piwoslaw

Neither trucks nor trains have regenerative braking, though.

Unless you're in Europe, where much of the rail network runs off electricity rather than diesel, in which case regenerative braking would be pretty easy to do.

Sometimes I wonder at US railroads. I see trains hooking on extra diesel locomotives for the trip over Donner Summit, then braking all the way down into Sacramento, when with an electric system and little ingenuity, the downhill train could be providing most of the power to one going uphill.

[Piwoslaw]

In order to pump electricity back into the railroad grid, there have to be other trains that can accept that energy at that moment. In the Donner Summit example (or any other uphill/downhill) for every decending train there should be one climbing the hill. Yes, it's doable.

Unfortunately, not all electrified raidroads allow regenerative braking, the Polish rail system being an example. The owner of the cantenaries (overhead wires) doesn't invest in new technology which would allow it to accept energy from braking trains because the 40-50 year old rolling scrap metal doesn't have regenerative braking, while the owners of the trains don't pay extra for regen when buying new locos because the rail system can't handle it. Circle closes. Even the new subway in Warsaw didn't think about regen, and subways are the best place for it - there are always trains that are braking and trains that are accelerating.

[dcb]

are the overhead wire guys in bed with the electric utility? They would have no motivation to upgrade in any event, sans regulation.

[daring4]

Originally Posted by dcb

are the overhead wire guys in bed with the electric utility? They would have no motivation to upgrade in any event, sans regulation.

If its anything like here the "overhead wire guys" are the utility(my job btw). All of the freight trains I have seen over here are hybrids, we do have a light rail downtown for passenger traffic but we only supply 12k volts to them, they own the rest.

[jamesqf]

Originally Posted by Piwoslaw

In order to pump electricity back into the railroad grid, there have to be other trains that can accept that energy at that moment.

But why should there be a railroad grid that's electrically separated from the general power grid? Conceptually, the down train lifts the up one, but in reality the down train dumps energy into the grid when it brakes. That energy might run the up train, or it might run a factory, traffic lights, or my PC.

Unfortunately, not all electrified raidroads allow regenerative braking, the Polish rail system being an example.

But as with the US using mostly diesel, the hurdles are social and political, not technical. We know how to build the machinery, but not how to motivate management to get off its collective butt and do it :-(