Spread of triple-trailer rigs has safety groups waving red flags. Truckers want them for economic reasons; foes say they are dangerous

Is the extra-large size of some trucks thundering down selected American highways a safe way to hold transportation costs down? Or is it instead a hazard to motorists - and destructive to bridges and roadways? These questions persist despite decades of debate in Washington and in state capitals. And now still larger trucks, ones hauling three trailers, are slowly coming into use, particularly in the West - much to the discomfort of opponents. Wyoming is the 11th state to permit them, and Montana may not be far behind. More expansion could lie ahead.

For economic reasons the trucking industry supports the use of extra-large vehicles.

For safety reasons other organizations, notably the American Automobile Association and the Insurance Institute for Highway Safety, oppose three-trailer trucks.

Pressure is on American trucking companies to trim costs in their continuing battle with railroads for freight shipped long distances. One of the ways that trucking firms seek to increase their productivity is by using, in some regions, trucks that pull three trailers behind their cabs, thus enabling one driver to do the work of several.

``We think they have a definite role to play, at least in some areas,'' says Neill Darmstadter, ``because they will permit lower transportation costs.'' Mr. Darmstadter is senior safety engineer of the American Trucking Associations.

In a study released late last year, the Insurance Institute concluded that two-trailer trucks, because of deficiencies in stability and driver training, are involved in crashes at a rate nearly three times that of single-trailer trucks. The safety problems of triple-trailer vehicles, Ian Jones says, is ``at least as bad as doubles, and ... you'd expect them to be worse.'' Dr. Jones is director of engineering research for the institute.

Congress's Office of Technology Assessment is studying the issue of motor-carrier safety. It will include a look at three-trailer trucks.

Final results will not be ready for a year, but Edith Page, the study's project director, says that already ``the research indicates that drivers are not always trained specifically to handle'' multitrailer rigs: ``The experience and training of the drivers is an important factor that comes out of data'' on serious accidents. She notes that ``there are some differences in handling these larger combination vehicles'' compared with the usual, one-trailer truck; specifically, the rear trailer is subject to physical forces that can ``result in rollover.''

Individual states must decide whether to permit these vehicles to use any of their roads.

In all states that now allow their use, these trucks are permitted on specific highways but forbidden to travel on most other roads.

Most states that allow these vehicles are in the far West, with a few in the Midwest.