What does the shale boom mean for transport?

Meanwhile, the price of natural gas fell by 57 percent between 2007 and 2012, in large part because of a spike in production of more than 25 percent.

Neither is it likely to be a short-term phenomenon.

The 2013 Annual Energy Outlook, published by the US Energy department, estimates that natural gas production in the US will increase by 44 percent over the next 30 years, with the majority of it coming from shale gas extraction.

Shale gas production is expected to more than double from the 7.8 billion cubic feet in 2011 to 16.7 billion in 2040.

For the moment, the US boom has not been reflected in Europe.

EU lawmakers are currently divided on whether to exploit their own supplies of shale gas. Supporters point to the increased GDP enjoyed by the US and argue that European businesses cannot compete with their American rivals if they continue to pay more than twice as much for energy.

Meanwhile, critics talk about environmental damage caused by hydraulic fracturing – or fracking – the process which cracks open rocks containing the gas.

But the shale gas revolution, whether at home or abroad, has implications for the transport sector.

Put simply, more shale gas means an increased supply of natural gas products as well as liquefied petroleum gas (LPG).

Some 45,000 tonnes of LPG are flared each month in the US, says Ernst Brandstaetter, an analyst with SHV Gas supply and risk management.

And the increased supply is not just coming from the US.

Russia exported 4 million tonnes of LPG in 2012, a figure which Alexey Rodichev, an analyst with energy giant Sibur, expects to double by 2015. Both are rapidly catching up on Qatar, the world's largest exporter of LPG.

The price cuts caused by the shale gas boom, together with the prospect of a long-lasting and secure supply, is also good news for LPG and could allow it to compete on a wider scale with diesel to fuel commercial and transit vehicles.

But is possibly even better for some of its rivals, such as compressed natural gas (CNG) and liquefied natural gas (LNG). In part because of its name, the price of LPG has been linked more closely to oil prices.

The profitability of using natural gas as a transportation fuel, or for exporting LNG, depends largely on the price differential between crude oil and natural gas.

The greater the difference between crude oil and natural gas prices, the greater the incentive to use natural gas.

For many years, the price of oil was between six and ten times that of natural gas – effectively parity since oil has around six times the energy content of gas. The ratio has varied between 1:20 and 1:30 over the past two years, with little sign that it will fall any time soon.

Price and ease of access have long been the trump cards for diesel and petrol against alternative fuels. A sustained natural gas boom could end these advantages for good.