Freight train effeciency ?

Bean

Here is a quote from a document on www.freightrailworks.com
"Freight trains move a ton of freight an average of 423 miles on a single gallon of diesel fuel."

Now how can that be possible ?

Bean.



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MarkS

Because they are diesel-electric hybrids.

Phil Pilgrim (PhiPi)

Steel wheels on steel rails — unlike tires on pavement — have very low rolling resistance, and railroad grades are kept to a minimum by design. Combine this with a train's momemtum once it gets rolling, along with the fact that it can keep rolling without stopping at intersections, and the quoted efficiency figure starts to make sense. Besides, a ton of freight is a very small fraction of a train's total payload.

-Phil

skylight

I bet that's not going uphill

pwillard

All true. Once up to speed, the efficiency of a freight train is over 400 as published by the Assiciation of American Railroads. ( over 400 short ton-miles ) as they say it. Some electric rail can even recover power through regenerative braking.

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There's nothing like a new idea and a warm soldering iron.

Dgswaner

another cool fact about diesel-electric engines is that they can "rewire" the engine on the fly to achieve what they require at the moment, torque, speed, resistance. they are quite the machine!

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James Long

Also.....there is a catch to that.

Rail roads do calculations to make sure the load (weight and number of cars) is close to optimum. A short train, or an overloaded train is not as effecient.

I worked for a locomotive repair facility for a while.

James Long

uxorious

My father-in-law retired from SP (UP) as an electrician. I toured the SP facility in downtown Sacramento several times before it was closed. A diesel locomotive is quite amazing in function. The DC traction motors that sit between the drive wheels on a train are impressively massive but look like a monster size encased slot car motor. My father-in-law rebuilt them. In his later years at UP (after the SP buyout) he did maintenance on the control units inside the locomotives. It's pretty amazing how the systems work. Simply put, it's an extremely efficient diesel generator that charges batteries and drives the DC motors. (can anyone say hybrid) That's why you hear the engines rev up so high when they just get rolling.... more current to the motors. Once up to speed, the locomotives really only need to maintain the system voltage. Think of the efficiency of a hybrid vehicle on the freeway and just apply that on a much larger scale.

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bobledoux

Even highway diesel trucks are quite efficient. A 50 ton truck might get 5 miles per gallon or 250 ton-miles per gallon. A truck can't match the railroad for direct shipping efficiency.

The real balance sheet is more complex. Consider the energy required to maintain the railroad system. Consider the energy required to maintain the truck and the road surface.

Tony Boersma

This discussion is really cool. I've never thought of it this way. My Toyota Echo can move about 4.8 ton-miles (my weight in tons * MPG) of freight (me) per gallon of gas.

Phil Pilgrim (PhiPi)

One of the efficiency advantages that trucks enjoy over rails is their more specific pickup and dropoff* points — for non-consolidated trailer-sized shipments, those being the actual source and destination. Transfers to and from a rail terminus and the rail car sorting and shuffling that occurs in between eat up a lot of time and energy.

-Phil

* I can't even write that without thinking of Car Talk and their chauffeur, Piekop Andropov!

Dave Hein

One of the main factors in fuel efficiency is air resistance.· There are several reasons smaller cars have better highway mileage than larger cars, but the major reason is a smaller frontal surface area.· Trains have extremely low air resistance compared to their mass.· This is one of the reasons they have such a high fuel efficiency.

Dave