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Comment by vaporstun | Hacker News Reader

MPJ - Miles per Joule

As we move toward alternative fuels, we need a fuel-independent metric.

Agreed. It'll have to be a measure of energy consumption per mile. Consumers will also have to develop an understanding of the relative cost of different energy sources.

Maybe we rate cars in Miles/Joule and rate energy sources in Joules/$. Makes the math pretty simple.

You might need to add some cargo/people capacity in there. A tiny electric car will have a hard time beating a diesel MAC truck for efficiency when it's hauling a few tons :)

Just as a Vespa would have poor gas mileage carrying heavy truck cargo - this has nothing to do with the energy source.

I thought that was the idea - removing different energy sources from the picture and looking at which vehicles are more efficient.

There is no intuitive way to convey what you are proposing. If you tried to move 4 tons of cargo, a big rig would use less energy than a Civic. If you are trying to get yourself across town, a Civic will use less energy than a big rig. It would be complicated and expensive to calculate the full spectrum of efficiencies for a vehicle under different cargo loads. Personally, I would use the data, but I suspect the average person would find multiple efficiency graphs to be overwhelming.

But 1 Joule of one energy does not cost the same as 1 Joule of another, which is why MPG gasoline and MPG diesel are not directly comparable

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