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EDVTS Calculation Options

EDVTS (Engineering Dynamics Corporation Vehicle Trailer Simulator) is a simulation analysis of the response of an articulated vehicle (either a passenger car pulling a standard trailer, or a commercial tractor-trailer vehicle) to driver inputs (accelerating, braking and steering). It is based on a program called TBSTT developed at the University of Michigan Transportation Research Institute. EDVTS determines how the vehicle responds to the inputs by generating the path, velocity, acceleration, tire force, and other data as a function of time.

Accident investigators can use EDVTS to determine how a driver may have lost vehicular control. By repeated adjustments of the throttle, braking and steering input tables, the user will converge on those driver inputs which match accident site evidence. EDVTS can also be used to study the handling effects due to changes in vehicle weight distribution, wheelbase, track width, CG height, tire friction, cornering stiffness, hitch or kingpin location and other parameters.

An extremely useful feature of EDVTS is the ability to quickly and accurately review the results generated from different input scenarios. Termed what if analysis, changes can be made to an isolated variable or set of variables and the effects are displayed immediately. For example, the sensitivity of the trajectory to various front/rear tire combinations can be studied simply by changing the tire data; the sensitivity to CG location can be studied by moving its position. However, the major purpose of EDVTS can be realized by changing the driver input tables (throttle, braking and steering) until the resulting trajectory matches the actual trajectory produced by the vehicle during a particular maneuver. Thus, the user learns how a driver's inputs may have affected the outcome of an accident.

The EDVTS engine does not present or use a Calculation Options dialog. It sets CalcMethodHeader.Options.CalcOptionsDlgIsUsed = FALSE (Vtsinput.cpp), so no calculation-options dialog is shown for EDVTS and the engine reads no calcFloat/calcInt/calcOption value. The one parameter historically exposed here — Roll Couple Distribution — is now taken from the tow vehicle's suspension data instead.

Roll Couple Distribution

Roll Couple Distribution sets the fraction of the tow vehicle's total lateral load transfer (roll couple) that is reacted by the front axle; the remainder is reacted by the rear axle. It is expressed as a fraction (units %/100) in the range 0.00 to 1.00. The default value is 0.55 (55 percent of the roll couple carried by the front axle).

For EDVTS this value is not entered through a Calculation Options dialog. It is set on the vehicle editor's suspension screen and read by the physics engine from the tow vehicle's suspension data, Vehicle[0].Wheel[0][0].Suspension.RollCoupleDist (Vtsinput.cpp; the former Event.Info.CalcOptions.calcFloat[0] path is commented out in the source).

Within the physics model, this parameter corresponds to the FORTRAN-heritage lateral load transfer coefficients gam1 (front axle) and gam2 = 1 - gam1 (rear axle) for the tow vehicle, which apportion the lateral weight shift used to compute the individual tire normal loads during cornering.

Note: An event still carries a legacy calculation-options field (calcOptions.calcFloat[0], default 0.55), but the current EDVTS engine does not read it. Because CalcOptionsDlgIsUsed = FALSE, gam1 is assigned only from Suspension.RollCoupleDist, so the roll couple distribution used by the simulation follows the vehicle editor's suspension setting.

Removed Options

Earlier versions of this help topic listed the terrain surface-search choices From First Polygon, From Previous Polygon and By Elevation as EDVTS calculation options. These are no longer part of the EDVTS Calculation Options dialog. The surface-search method is now selected in the separate Get Surface Information Options dialog (Options menu), which offers From First Polygon, From Previous Polygon, From Previous Polygon (Sorted) and By Elevation.

Source topic: CalcOptEDVTS.htm — updated from source code (HVEINV-64, Physics) 2026-07-05.

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