According to NHTSA's 2011 Traffic Safety Facts , passenger vehicle occupant fatalities continued the strong decline that has been occurring recently. In 2011, there were 21,253 passenger vehicles fatalities compared to 22,273 in 2010, and that was a 4.6% decrease. However; large-truck occupant fatalities increased from 530 in 2010 to 635 in 2011, which is a 20% increase. This was a second consecutive year in which large truck fatalities have increased (9% increase from 2009 to 2010). There was also a 15% increase in large truck occupant injuries from 2010. Moreover, the fatal crashes involving large trucks increased by 1.9%, in contrast to other-vehicle-occupant fatalities that declined by 3.6% from 2010.The 2010 accident statistics NHTSA's report reveals that large trucks have a fatal accident involvement rate of 1.22 vehicles per 100 million vehicle miles traveled compared to 1.53 for light trucks and 1.18 for passenger cars. This translates to a fatal accident involvement rate of 32.35 vehicles per 100,000 registered large trucks compared to 17.02 for light trucks and 13.09 for passenger cars. These statistics indicate that large trucks account for a disproportionately large number of fatal crashes compared to any other type of vehicle (excluding motorcycles) even though they account for only a small fraction of registered vehicles.However, testing tractor trailer combinations on the test track is a cumbersome, potentially dangerous, and expensive process. An alternate means to test such vehicles is to use Hardware-in-the-Loop (HIL) simulation technologies to test Electronic Stability Control (ESC) and other emerging advanced technologies intended for highway safety.The HIL simulation environment incorporates multiple software environments interacting with actual hardware. In such a simulation, the accuracy of the software models is critical to the accuracy of the simulation results. This paper outlines the modeling of a Volvo tractor and two trailers in TruckSim, used by the HIL system at NHTSA.