Taxis are another cheap way to get around, with a 90p flagfall then 60p per kilometre.
That amounted to almost 5000 pieces of litter per kilometre of shoreline cleaned around Northern Ireland's coast.
In 1994, 530 items of plastic were found per kilometre of beach compared to more than 1, 000 in 2004.
He proposes a hefty passenger tax on aviation of 3.6 pence (74 cents) per kilometre which would flatten demand growth to 1-2% each year.
Northern Ireland's beaches are some of the untidiest in the UK, with litter levels per kilometre more than double that found on most other beaches.
Porsche expects the 918 Spyder to emit 70 grams of carbon dioxide per kilometre travelled, which is about the same as the output of a tiny city car.
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"Anyone who's filled up at a petrol station recently will realise that the ability to recharge overnight at 1-3 pence per kilometre is extremely attractive, " Transport Secretary Philip Hammond told BBC News at the launch.
The population density in the Russian Far East is barely one person per square kilometre.
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There are also huge differences in population density across the country, with the population per square kilometre ranging from nine in Eilean Siar (the Western Isles) and the Highlands to 3, 395 in Glasgow.
Extrapolating from Dr Freund's laboratory experiments, the strain in a real-life geological fault such as the San Andreas could, as it shifted, generate hundreds of thousands of amperes per cubic kilometre in a fluctuating pattern that would cause very low frequency radio waves to be emitted, thus disrupting the ionosphere.
The line makes a kilometre of paper every minute, runs non-stop and requires only 14 workers per shift.
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