The study observes that while in the EU as a whole, the ration of total tonne-km by inland modes to GDP grew by 9% between 1993 and 2003, the UK however, experienced a modest decoupling: bBetween 1997 and 2004, GDP increased in real terms in the UK by a fifth while the volume of road freight movement remained stable.

The study examines 12 possible causes of this decoupling, assesses how significant they are and considers whether this has actually led to environmental improvements. It finds that 3 possible causes account for two thirds of the decoupling and importantly, that the environmental gains are likely to have been much smaller than the statistical decoupling suggests. The three causes which can be quantified are:

a.The increased increased penetration of the British road freight market by foreign hauliers. Their movements are not currently recorded in DfT statistics. If they were recordec, McKinnon estimates that the degree of decoupling would have been around 30% lower.

b. An increase in the real cost of road freight transport accounts for another 12% of the decoupling.

c. Modal shift: Just under a quarter of the decoupling can be attributed to a decline in road's share of the freight market. As rail and water-based services generate few externalities per tonne-km, this trend has yielded sustainability benefits.

The study notes that of the causes, two others are significant:

As regards distribution networks in the UK, the geographical centralisation of activities in this country has gone as far is it can go. We cannot concentrate any more.

Second, it notes - and stresses that this is likely to be significant - the fact that we are relocating our production activities to other countries: 'The off-shoringof manufacturing to Eastern Europe and the Far East reduces the freight transport intensity of western economies, but at a global scale is increasing CO2 and other emissions.'