At present less than 6% of total British freight transport is accounted for by rail, compared with 15% in France and 21% in Germany.

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Most long-term predictions suggest that, despite weak growth over the past couple of years, the total of freight-tonne kilometres flown will expand by around 6% a year over the next couple of decades (see chart).

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The sooner other countries follow their example and base transport taxation on total costs, the sooner rail freight will be able to compete.

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However, heavier, less urgent and low value per pound shipments will increasingly shift towards the sea route as companies thrive to manage their total distribution costs efficiently, which would limit the growth in air freight segment.

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But the relative proportion of total fuel use can be extrapolated by comparing passenger kilometers traveled versus tonne-kilometers for freight on the top 10 carriers.

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Proponents note that the overall cost of the project would be recouped within a few decades, as the volume of tunnel freight transport activity increased, reaching an estimated 3 percent of the world's total physical cargo or 100 million tons annually.

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