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Understanding “Ton-Miles” and their Impact on our Choices

In a recent blog post, I mentioned the decentralization of food (or in broader terms, the decentralization of stuff). One benefit of increasing local production is a reduction in the impacts of freight transport. A lot of our customers include freight transport in their emissions inventories and so I decided to take a little closer look.

Freight or shipping activity is measured in ton-miles. One ton-mile is the equivalent of shipping one ton of product, one mile. To put this in context:

What is a ton-mile?

One ton-mile is the equivalent of shipping one ton of product, one mile.

For example:

  • One ton-mile is the equivalent of shipping one gallon of milk about 225 miles.
  • Importing a piece of furniture that weighs 100 lbs. from China to Seattle incurs over 300 ton-miles.
  • 562 billion ton-miles were incurred in the shipment of coal in the US in 2002 alone.

Not all ton-miles are equivalent in terms of their impact – the EPA’s Climate Leaders program identifies different greenhouse gas emissions factors for different modes of transport, as follows:

GHG Emissions for Different Modes of Transport

Intuitively, it seems obvious that air transport would incur greater emissions than rail or ship transport. However, I found the magnitude to be startling – shipping by air incurs 60 times the emissions as shipping the equivalent weight by rail.

Let’s put this in context with a couple of examples.

How about those bottles of San Pellegrino water from Italy? The iconic glass bottles (including their contents) weigh a little over one pound. To get to Seattle, each bottle has to travel some 6000 miles. That is about 3 ton-miles per bottle. Assuming shipment through a combination of waterborne and truck transport, there’s probably not much more than one pound of CO2e emissions incurred with each bottle imported. That’s roughly the same emissions incurred in driving a car one mile–not much on a bottle-by-bottle basis.

Now let’s compare a sushi dinner. Let’s assume we eat a ½ lb of fish and it’s all imported from Japan, about 4800 miles away. Being fish, it’s probably transported by air. So that’s about 2400 lb-miles or a little over one ton-mile. That’s fewer ton-miles than a bottle of San Pellegrino but, being air transported, our sushi dinner incurs about 3.4 lbs of CO2e in freight-related emissions or about three times as much as the bottle of San Pellegrino.

Let’s consider a BMW 740i Sedan which weighs about 4,300 lbs. Assume it’s shipped by sea from Germany to New York (about 4000 miles), then by truck from New York to Seattle (about 3000 miles). That’s about 8,600 ton-miles by ship plus about 6,450 ton-miles by truck. That translates to about 1350 lbs of CO2e emissions due to shipping. That’s about the same emissions that would be generated by driving the car 1300 miles.

Finally – how about those 562 billion ton-miles of coal shipment in the US? If that’s by rail, then it translates to about 15 million tons of CO2e, just from the transport of coal.

So what does this all mean? The freight-related emissions associated with any one of the products we buy aren’t that significant. However, add up the emissions from all the products we ship and the numbers get very big, very quickly.