Rig on a roll

THE monster 18-wheel trucks that hurtle along America's highways carry most of the nation's freight. There are reckoned to be some 1.3m of these “semi-trailers”, as the combination of a tractor unit and trailer are known. Such vehicles are called articulated lorries in Britain, although they tend to be a bit puny compared with American rigs that can weigh 32,000kg (70,000lbs) or more. Not surprisingly the big semi-trailers take skill to handle—and they consume a lot of diesel. But a new development could reduce fuel consumption and give truckers one less thing to worry about when on the open road.

The work involves fitting wind-deflecting devices under the trailer of a semi to make the rig more aerodynamically efficient. The devices direct oncoming air around the trailer in such a way that it increases pressure in the area of the slipstream immediately behind the vehicle. Ordinarily, this is a low-pressure area which has the effect of sucking the truck backwards, something that adds to the rig's fuel consumption.