Heavy Truck Dynamic Rollover: Effect of Load Distribution, Cargo Type, and Road Design Characteristics

Abstract

The dynamic response of a five-axle tractor–trailer unit carrying loads of various weights was evaluated under actual operating conditions as the vehicle traveled along roadway curves with various radii. A data acquisition system (DAS) was designed and developed to record information for a vehicle moving at highway speeds. The DAS used sensors interfaced to a central processing unit. The test runs were performed over a total of 1,110 km of highway under three load configurations: empty, loaded with less than the truck load, and loaded with bottled spring water packed in boxes. Data on lateral, longitudinal, and vertical accelerations; steering activity; vehicle speed; and roll angle of the trailer were recorded. It was found that in most cases the average level of lateral acceleration exhibited on both the tractor and the trailer exceeded expected values calculated for the curves on the basis of geometric design characteristics. Comparisons of actual results with theoretical considerations confirmed this observation. Analyses of field data indicated that under certain motion and load conditions, the occasional peak lateral acceleration values generated were in the vicinity of rollover threshold values estimated for the instrumented vehicle. The results also showed that although the vehicle traveled at or below the posted speed limit in the majority of cases, lateral accelerations recorded for the trailer exceeded expected lateral accelerations under all load configurations. This suggests the need to consider establishing speed limits on curves that take into consideration the different responses of heavy trucks compared with those of smaller and lighter vehicles.