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Accidents involving light truck-trailer combinations

A comparatively small proportion of road freight transport is accounted for by light truck-trailer combinations. These are two-axle trucks with a gross vehicle weight of up to 7.49 tonnes and what is generally a single-axle trailer. Together they have a gross weight of just under 12 tonnes. They are generally covered by a lightweight tarpaulin structure for transporting lightweight goods that require a lot of space, such as foam or insulation materials, empty drinks cans or plastic tubing.

Even when fully loaded, the vehicles weigh less than empty conventional truck trailers with a permissible gross vehicle weight of up to 40 tonnes, although they represent a similarly sized target for crosswinds. In strong winds or storms there are therefore frequently reports of accidents in which light truck-trailer combinations overturn either completely or partially. Often it is only the unladen trailer that is affected. The objective of the research project was therefore to analyze crosswind accidents involving light truck-trailer combinations, in particular, and investigate how they arise and what can be done to prevent them.

Traffic counts at a number of German motorway interchanges revealed that light truck-trailer combinations accounted for around 1.5% to 2% of all goods vehicles over 3.5 tonnes. They are generally not prominent in the accident statistics. However, police accident reports mention crosswind as the accident cause more often for these vehicles than for trucks with a gross vehicle weight of over 7.5 tonnes (around 12% of accidents rather than 3%). A retrospective internet search of overturned light trucks and trailers between 2010 and 2015 confirmed the hypothesis that these vehicles are particularly vulnerable to strong winds. Almost all the incidents researched were found to coincide with storms over Germany.

The tendency to overturn in crosswinds was investigated with the help of computer simulations. Both a typical 12-tonne light truck-trailer combination, consisting of a two-axle tractor truck and a single-axle trailer, and two forms of 40-tonne truck-trailer combination were modeled. A drive straight ahead on an even road surface was simulated with a wide variety of crosswinds. The calculations forecast that the situation becomes critical for unladen light truck-trailer combinations as of a wind force of 7. Although conventional truck-trailer combinations in the 40-tonne class are also not free of risk in strong winds, this effect is only seen with significantly stronger winds (as of a wind force of 9). Although no further increase in the numbers of very light high-volume trucks is to be expected, these and very similar vehicles will continue to be seen on the roads. UDV demands that these vehicles be kept off the roads on days when a deep depression is forecast. This only happens a few times a year and would be an easy and effective way to prevent these avoidable accidents from happening.