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In this paper, a real-world accident that involved a tractor-semitrailer that lost its brakes on a steep downgrade is analyzed. The crash was caused by brake loss due to massive overheating caused by inoperative brakes, driving too fast for conditions, and driving in an improper gear. The effect on brake temperatures from prior uphill and downhill stretches encountered just before the crash is considered. The crash is analyzed using a Microsoft® Excel spreadsheet-based transient brake model for three sets of published brake temperature modeling methodologies and parameters: The Grade Severity Rating System developed by NHTSA (GSRS), a model developed by the University of Michigan Transportation Research Institute (UMTRI), and a model developed by Rudolf Limpert (Limpert). A fourth and different approach utilized a heavy truck simulation (HVE-SIMON™) with HVE Brake Designer®. The results of this analysis using the four models are compared.

Construction of a transient model for a Class 8 tractor-trailer negotiating mountain terrain is presented. Four basic brake models for free and forced cooling (GSRS, UMTRI, Limpert, and HVE Brake Designer®) are converted to consistent units. The units have been reduced to those accepted variables in the thermodynamic/heat transfer literature (hc, A, cp, M), thereby facilitating model comparison and coefficient selection from the published literature. The data has been compared to real test published data. The effect of varying the desired vehicle speed, vehicle weight, number of adjusted brakes, and slope magnitude on brake drum temperatures is explored.

CARAT (Computer Aided Reconstruction of Accidents in Traffic) is a Microsoft Windows® based simulation program. CARAT allows for simulation of pre-collision, collision, and post-collision dynamics in a graphical environment. CARAT can model cars, trucks, trailers and tractor/semi-trailers. CARAT-3, released in the mid-90's, is a three degree-of-freedom (3 DOF) model, with three dependent DOF, and operates mathematically in a two-dimensional (2D) graphical environment. Vehicle graphics can be viewed in three dimensions (3D). CARAT-4 implements 3D multi-body models with 10 DOF for the car model, and up to 26 DOF for the truck and trailer model. CARAT is a time forward kinetic simulation, but can also be used to perform kinematic calculations forward and backwards in time. Both CARAT-3 and CARAT-4 implement a momentum-based collision algorithm.

The flexibility of flat bed trailers is shown to be an important consideration in determining the static roll threshold for a loaded Class 8 tractor trailer. The development of an easy to use static roll threshold model using Microsoft® Excel's nonlinear equation solution capability provides a tool that should be useful to the trailer designer, dock loading manager and the traffic safety manager responsible for the training of drivers. It can be seen for low stiffness flat bed trailers that the trailer torsional stiffness is a more important parameter than typical suspension or tire stiffness. Further, even for “stiff” flat bed trailers the use of the rigid body roll criteria (T/2h) or the 2-D “planar” model can produce significant error in many practical loading configurations.