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It's wasn't obvious to me that trucking is much less energy effecient than rail. According to treehugger.com rail achieves "400 ton-miles per gallon whereas tru

It's wasn't obvious to me that trucking is much less energy effecient than rail. According to treehugger.com rail achieves "400 ton-miles per gallon whereas trucks currently hover around 130 ton-miles per gallon" [1]. I wonder why that would be - rubber tires vs steel-on-steel? Traffic? There isn't much traffic during the majority of a long-haul and the last few miles have to be done by truck anyway. [1] https://www.treehugger.com/cars/rail-versus-trucking-whos-the-greenest-freight-carrier.html https://www.treehugger.com/cars/rail-versus-trucking-whos-th...

hirsin 9y ago
Braking and acceleration - once you get x tons of anything moving, it generally wants to keep moving. Trains are tens of times longer than trucks, brake significantly less often, and have a lot more horsepower for acceleration.
- int_19h 9y ago
  The other thing is, you can string wires along the rails relatively easily, and power everything directly with electricity - which offers substantial savings from efficiency of large scale power generation, even accounting for distribution losses. Better yet, you can then use regenerative braking, and feed energy back into the line. I do believe there's some benefit from the tracks themselves as well, though. Surely there's a lot less friction (per ton of weight) between the train wheels and steel rails, than there is between truck tires and the road?
  - libertyEQ 9y ago
    >you can string wires along the rails relatively easily, and power everything directly with electricity - Except all freight trains in the US have 6600 HP diesel engines, usually ~6-8 engines per 100 cars from what I've seen (which is mostly coal).
    - int_19h 9y ago
      US is an outlier in that regard. In other developed countries, railroads are mostly electrified.
- em3rgent0rdr 9y ago
  I'd also say increased engine efficiency resulting from being able to have a bigger engine to move more tons.
- pwg 9y ago
  Lowered overall wind resistance also plays a significant part. With Semi's, each separate truck has to endure its own wind resistance independently. With a train, each rail car effectively drafts the car in front, producing significant reductions in wind resistance for all cars behind the locomotive. This site (https://www.energy.gov/eere/vehicles/parasitic-loss-reduction-research-and-development https://www.energy.gov/eere/vehicles/parasitic-loss-reductio...) quotes wind resistance, braking, and rolling resistance as responsible for a 45% reduction in efficiency. This site (https://www.nap.edu/read/13288/chapter/7 https://www.nap.edu/read/13288/chapter/7) has a table that separates the factors out. Of the parasitic losses, aerodynamic losses (i.e., wind resistance) is responsible for consuming 53% of the motive power.
emiliobumachar 9y ago
A small part of it is air resistance. A train has a lot less frontal area per ton.

hirsin 9y ago

Braking and acceleration - once you get x tons of anything moving, it generally wants to keep moving. Trains are tens of times longer than trucks, brake significantly less often, and have a lot more horsepower for acceleration.

int_19h 9y ago
The other thing is, you can string wires along the rails relatively easily, and power everything directly with electricity - which offers substantial savings from efficiency of large scale power generation, even accounting for distribution losses. Better yet, you can then use regenerative braking, and feed energy back into the line. I do believe there's some benefit from the tracks themselves as well, though. Surely there's a lot less friction (per ton of weight) between the train wheels and steel rails, than there is between truck tires and the road?
- libertyEQ 9y ago
  >you can string wires along the rails relatively easily, and power everything directly with electricity - Except all freight trains in the US have 6600 HP diesel engines, usually ~6-8 engines per 100 cars from what I've seen (which is mostly coal).
  - int_19h 9y ago
    US is an outlier in that regard. In other developed countries, railroads are mostly electrified.
em3rgent0rdr 9y ago
I'd also say increased engine efficiency resulting from being able to have a bigger engine to move more tons.
pwg 9y ago
Lowered overall wind resistance also plays a significant part. With Semi's, each separate truck has to endure its own wind resistance independently. With a train, each rail car effectively drafts the car in front, producing significant reductions in wind resistance for all cars behind the locomotive. This site (https://www.energy.gov/eere/vehicles/parasitic-loss-reduction-research-and-development https://www.energy.gov/eere/vehicles/parasitic-loss-reductio...) quotes wind resistance, braking, and rolling resistance as responsible for a 45% reduction in efficiency. This site (https://www.nap.edu/read/13288/chapter/7 https://www.nap.edu/read/13288/chapter/7) has a table that separates the factors out. Of the parasitic losses, aerodynamic losses (i.e., wind resistance) is responsible for consuming 53% of the motive power.

emiliobumachar 9y ago

A small part of it is air resistance. A train has a lot less frontal area per ton.