The double-deck trailer is the unsung hero of UK logistics. Few road freight innovations have brought such economic and environmental benefit and yet been largely confined to this country. The double-deck is a form of ‘high-capacity transport’ made possible by relatively generous height clearances across the UK road network. Surprisingly, unlike most other European countries, Britain has no legal limit on trailer height. Its 5 metre ‘custom and practice’ limit is around a metre higher than that in most other countries, allowing operators to carry two layers of pallets. This expands load space vertically rather than horizontally as has happened elsewhere.
I co-authored the first study of double-deck trailers exactly 25 years ago. It forecast that they would have a bright future, particularly as an increasing share of road freight was of low density and requiring greater cubic capacity. I returned to the subject in 2010 when a European Commission plan to standardise maximum trailer height at 4 metres would have resulted in the UK double-deck fleet being phased out. I estimated that, on an annual basis, this would have increased UK road haulage costs by £300 million and CO2 emissions by 320,000 tonnes. Thankfully, the plan was dropped. Since then the number of double-deck trailers in the UK has risen sharply.
Nobody knows exactly how many currently operate on UK roads because there’s no trailer registration scheme. Data from the government’s annual road freight survey suggested that their share of the trailer fleet rose from 3% to 7% between 2004 and 2013. Unfortunately, 2013 was the last year this survey separately categorised them. Don Bur, a major producer of double-decks, estimates they now represent 10% of all trailers, numbering around 25,000, with 2500-3000 more manufactured each year. Many of the new ones are longer-semi trailers (LSTs), allowing operators to carry up to 60 pallets. That’s an impressive 130% more carrying capacity that the standard 26 pallet single-deck articulated lorry.
A government report in 2007 extolled the virtues of double-decking, suggesting that 48% reductions in fuel use and CO2 emissions per pallet were possible. Since then the development of new double-deck configurations, improved aerodynamic profiling, lightweighting and the installation of roof-mounted solar panels have further enhanced their contribution to road freight decarbonisation. It is surprising, therefore, that no reference was made to them in the government’s Decarbonising Transport plan published last year. Perhaps the government considers the double-decking trend to have enough market momentum without the need for public policy support.
Double-decks do have their downsides. Their greater height and higher centre of gravity increases the incidence of bridge strikes and roll-overs, though adherence to advice given by the HSE on how to operate them safely helps to minimise these additional risks. As climate change increases the frequency and intensity of storms they will become more vulnerable to cross-winds. Their greater height would also make the catenary electrification of UK motorways for trucks more challenging, but still possible. So, on balance, we should be grateful that so much of our freight now moves in these giants of the motorway.