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Calculation Options for EDCRASH

EDCRASH (Engineering Dynamics Corporation Reconstruction of Accident Speeds on the Highway) is an analysis used to reconstruct single and two vehicle accidents. EDCRASH is based on the Calspan Reconstruction of Accident Speeds on the Highway (CRASH) and includes refinements and enhancements provided by the National Highway Traffic Safety Administration (NHTSA) and Engineering Dynamics Corporation. The program determines the conditions of impact, including the impact speeds and delta-V of the vehicles, using information obtained from vehicle and accident site inspections.

The output generated by EDCRASH depends on the amount of information supplied. The minimum information required is a description of the vehicle damage. Therefore, when accident site information is not supplied, the resulting output will be limited to an analysis of the severity of impact, including delta-V (speed change) and magnitude and principal direction of force. When accident site information is supplied, the output will also include the speed of the vehicle(s) at impact.

EDCRASH is a useful tool for investigating the circumstances of an accident. These circumstances include the effect of human, vehicle and environmental factors on the pre-impact and post-impact events.

An extremely useful feature of EDCRASH 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. Only the parameters that change need to be modified; the HVE Event Editor saves all the previously entered information. For example, the sensitivity of the results to impact positions, rest positions or principal direction of force can be analyzed by merely changing the event and re-executing.

The EDCRASH Calculation Options dialog contains four groups of options — Program Options, Separation Velocity Basis, Consistency Checks and Simulation Convergence Criteria — plus an Apply Defaults button that restores all values in the dialog to their factory defaults.

Program Options

Four check boxes enable or disable individual EDCRASH calculation procedures:

  • Common Velocity check — When checked, EDCRASH tests the computed separation velocities of the two vehicles to be sure they are compatible with the assumption of a common velocity at maximum engagement (internal physics variable ComVelChkIsUsed). Default: checked.
  • Modify Departure Angle — When checked, EDCRASH tests, and possibly modifies, the departure (separation) angles based on the computed post-impact rotation and rollout velocity (internal physics variable ModifyGamSepIsUsed, applied by ModifyGamSep()). Default: checked.
  • Auto - Set Rot/Lat Skidding — When checked, EDCRASH automatically determines whether each vehicle experienced rotational/lateral skidding during its post-impact trajectory, rather than relying solely on the user-entered skidding flags (internal physics variable AutoRotLatSkidIsUsed, applied by AutoSkid()). Default: checked.
  • Include Angular Momentum Solution — When checked, EDCRASH includes a conservation of angular momentum solution in addition to the standard linear momentum solution (internal physics variable AngMomentumIsUsed). Default: unchecked. Note: this check box is disabled (grayed out) in the current version of the dialog and cannot be changed.

Separation Velocity Basis

This group of radio buttons selects the method EDCRASH uses to compute the vehicles' separation velocities (internal option calcInt[0]; see TRAJ_SIM, SUST_CONTACT and ITERATE_ON_SIDESLIP in Cradef.h). The default is Normal.

  • Normal — Choosing Normal causes EDCRASH to perform its standard, energy-based calculations to provide an estimate for separation forward, lateral and angular velocities and departure angle.
  • Trajectory Simulation — Choosing Trajectory Simulation causes EDCRASH to perform its standard, energy-based calculations (same as choosing Normal), and then use the separation velocities and departure angles as the initial conditions for a trajectory simulation (SetTrajSimulation). The simulation is run iteratively until the simulated trajectory matches the evidence at rest (and, if entered, end-of-rotation and point-on-curve positions) within the tolerances entered in the Simulation Convergence Criteria group below, or until the specified number of runs is reached.
  • Sustained Contact — Choosing Sustained Contact causes EDCRASH to use a weighted drag factor based on the wheel lock-ups and weights of the individual vehicles (SetSustainedContact, applied by SustainedContactSpeedCalc()).
  • Iterate on Sideslip — Choosing Iterate on Sideslip requests an iterative solution on vehicle sideslip angle (SetIterateOnSideslip). Note: this option is not supported by the current EDCRASH physics engine; selecting it causes the event to terminate with an error (see Crainput.cpp).

Consistency Checks

EDCRASH performs several tests that compare independently computed results and issues warning messages when they disagree by more than a user-specified tolerance. The tolerances are:

  • PDOF Range, +/- (deg) — Warning range for compatibility of the principal directions of force of the two vehicles (internal physics variable PdofWarnRange; stored internally in radians). Default: 10 degrees.
  • Delta-V Range, +/- (%/100) — Warning range for compatibility between the damage-based and momentum-based delta-V results (internal physics variable DeltaVWarnRange). Default: 0.10.
  • K.E. Range, +/- (%/100) — Warning range for the kinetic energy compatibility test (internal physics variable KEWarnRange). Default: 0.50.
  • Newton's 3rd Law Range, +/- (%/100) — Warning range for the test comparing the collision force magnitudes on the two vehicles, which should be equal and opposite per Newton's third law (internal physics variable CollForceWarnRange). Default: 1.00.

Simulation Convergence Criteria

These entries apply only when the Separation Velocity Basis is set to Trajectory Simulation; they are disabled for the other choices. They control the iteration used to match the simulated post-impact trajectory to the physical evidence:

  • Number Of Runs — Maximum number of trajectory simulation iterations per vehicle (internal physics variable MaxTrajRuns). Default: 5.
  • Rest Error, X-Y (%/100) — Allowable error in the simulated rest position (internal physics variable Traj_error_range[0]). Default: 0.10.
  • Rest Error, Heading (%/100) — Allowable error in the simulated heading angle at rest (Traj_error_range[1]). Default: 0.10.
  • EOR Error, X-Y (%/100) — Allowable error in the simulated end-of-rotation position (Traj_error_range[2]). Default: 0.15.
  • EOR Error, Heading (%/100) — Allowable error in the simulated heading angle at end of rotation (Traj_error_range[3]). Default: 0.15.
  • POC Error, X-Y (%/100) — Allowable error in the simulated position at the user-entered point on curve (Traj_error_range[4]). Default: 0.15.

Apply Defaults

Pressing the Apply Defaults button restores every option in the dialog to its factory default value (the defaults listed above).

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

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