Though the trucks consist of only 3% of the total registered vehicles in the United States, truck accidents have been a major concern due to the property damage and loss of lives involved. Growth trends show that the truck travel will reach 1 trillion vehicle miles by the end of the year 2000. This increase in truck travel poses a major threat to the safety of both passenger cars and trucks. To improve the safety of the trucks as well as the passenger cars, understanding of the factors affecting the truck safety is essential. Models developed in the past were mostly regression models which tried to relate the truck accidents to the geometry of the highways. But most of these models did not consider all the factors affecting the safety of the trucks. Simulation models were developed in the past to study the dynamic vehicle response to different highway geometry especially, on exit ramps where most of the rollover accidents occur every year. But not enough research was done in the past on the weather and surface conditions affecting the truck safety.

The objective of this study is to develop a graphics-based computer simulation model to test the trucks for different geometric features, surface conditions, and truck characteristics on exit ramps and to gain a better understanding of the factors affecting the safety of the trucks.

A high-level simulation language SIMSCRIPTII.5 was used in the study to develop a simulation model. To make the model is to understand, graphical windows and animation were included in the model. Three exit ramps were tested in this model. Two of these ramps are existing ramps in southwestern Virginia and they had rollover accidents reported on them in the past. The parameters and other surface and geometric conditions can be changed at any time during the simulation. The model indicated that deceleration lengths provided may not be sufficient for heavy trucks traveling at higher speeds to reduce their speeds to the safe speed limits on the ramps. The posted speed limits may not be suitable for heavy trucks especially when the surface is not dry. The model also indicated that the tractor-semitrailers are more exposed to rollovers than any other type of trucks.