As trucks roll down the road, they create dips and bumps in the pavement. When other trucks run over the bumps, they vibrate in the same way, making those hills and valleys deeper, according to research by engineer Don Margolis of the University of California-Davis.
That makes for an uncomfortable, possibly unhealthy ride for truckers, as well as damaged roads, he said.
Margolis used data on trucks and bumpy road surfaces to build a computer simulation. Although it's known that heavy trucks damage roads, no one had previously shown that the shape and pattern of bumps was so important, or that trucks reinforce the rutting damage caused by other trucks, he said.
It's not yet clear whether total weight, or the way the weight is loaded on individual axles, is more important in causing damage.
Moving trucks have two types of vibration caused by road surfaces. "Rigid body" movements are bounces, rolls and heaves of the whole vehicle, with a frequency of one or two a second. "Beaming" movements are caused by bending of the truck frame, and have a higher frequency. According to the computer model, roads where trucks travel at lower average speeds develop bumps, causing rigid body movement, while higher-speed stretches develop beaming problems.
The computer model shows that it is possible to distribute weight to isolate the driver's cab from beaming or from rigid body movement, but not from both, Margolis said. In fact, truckers already try to smooth their ride by adjusting the coupling between tractor and trailer, he said. This trial- and-error approach can give them better isolation from the road surface - but it also can break regulations requiring 14,000 pounds of load to be on the front axle.
The study is published in the January issue of the journal Vehicle System Dynamics.