The IRU hopes the evidence will help combat a political trend to boost the amount of "combined transport" where road freight is transferred to rail or waterways for a large part of its journey in an effort to reduce congestion and emissions.

The study by German consultancies IFEU and SGKV compared the energy consumption of 14 European long-distance combined transport routes with the equivalent journeys by road alone.

Energy consumption could be halved on certain routes, such as Antwerp to Milan, when containers only were put on to trains. But savings were far less when semi-trailers were used and often non-existent when whole trucks were put on trains, it found.

The Community of European Railways estimates that rail transport uses one quarter the amount of energy that equivalent road journeys, with corresponding reductions in greenhouse gas emissions blamed for global warming.

One reason for the stark difference in the claims is that carrying trucks or trailers on trains requires much more energy per tonne of freight carried than carrying bulk items such as coal.

The European Commission wants to increase rail transport's share of freight transport to 15 percent from eight percent by 2020 and says it will boost combined road-rail-water transport. In 1970 railways carried around 21 percent of EU freight.

"For 20 years we have been hearing that combined transport is the solution," IRU Secretary General Martin Marmy told a news conference to present the report.

"Combined transport is more than anything a political tool which allows politicians to justify penalties and restrictions on road transport...and it permits them to avoid investment in (road) infrastructure."