Traffic Crash Investigation Tools

01 Scene conditions

• Historical Weather, Sun & TwilightPulls archived hourly weather, sun position and twilight times for a location and date. Establishes what the surface and the light were doing at the moment of the crash.

02 Vehicle geometry

• Vehicle Lookup (NHTSA vPIC)Decodes a VIN against the NHTSA vPIC database for year, make, model and body class. The starting point for weights and dimensions.
• Case Vehicle LibraryHolds the vehicles in your case with curb weights, dimensions and occupants. Other worksheets draw from it so each figure is entered once.
• Longitudinal Center of MassLocates the longitudinal centre of mass from axle weights and wheelbase. Needed for momentum, rollover and load-transfer work.
• Static Stability FactorStatic stability factor from track width and centre-of-gravity height. A first-order indicator of rollover propensity.

03 Drag factor & friction

• Drag Factor from Drag SledConverts drag-sled pull readings into a drag factor for the surface. Averages repeated pulls to reduce operator variance.
• Drag Factor from Test SkidDerives drag factor from a controlled test skid at a known speed. The most defensible surface value when you can run one.
• Grade Adjustment of Drag FactorAdjusts a measured drag factor for roadway grade. Uphill and downhill change the effective value materially.
• Slope, Grade & SuperelevationConverts between percent grade, degrees and superelevation. Feeds every grade-sensitive speed worksheet.
• Braking EfficiencyApplies braking efficiency when not all wheels contributed. Handles partial braking, failed circuits and locked axles.
• Drag Factor from Deceleration RateConverts a measured deceleration rate into an equivalent drag factor. Useful with EDR or video-derived rates.
• Wet / Ice Adjusted Drag FactorAdjusts drag factor for wet, snow or icy surfaces. Pairs with the scene conditions lookup.
• Superelevation from Survey PointsComputes superelevation from surveyed cross-section points, for curves where a direct measurement is not available.

04 Speed from tire marks

• Minimum Speed (Slide to Stop)Minimum speed from a skid that ended in a full stop. The workhorse skid-mark equation.
• Combined Speed (Multiple Segments)Combines skid segments with different drag factors into a single speed. For marks that cross changing surfaces.
• Speed at Start of SkidSpeed at the start of a skid given a known impact speed. Adds back the energy lost before contact.
• Skid Distance from a Known SpeedDistance needed to skid to a stop from a known speed. Runs the slide-to-stop relationship in reverse.
• Tire Mark Classification HelperHelps separate skid, scuff, yaw and imprint marks by their characteristics. Classification decides which equation applies.

05 Yaw, radius & curve

• Radius from Chord & Middle OrdinateRadius of a curved tire mark from chord length and middle ordinate. The measurement critical speed depends on.
• Critical Speed from Yaw MarkCritical speed from a yaw mark radius and drag factor. For vehicles that scuffed rather than braked.
• Critical Speed with Grade & CrownCritical speed corrected for grade and roadway crown. Cross-slope shifts the answer more than most expect.
• Lambourn Multi-Point Critical SpeedLambourn multi-point method across several chords of one yaw mark. Reduces the error of a single radius measurement.
• Design Curve SpeedDesign speed of a curve from radius and superelevation. Compares design speed against travelled speed.

06 Time, distance & velocity

• Uniform Acceleration SolverSolves uniform acceleration for whichever variable is missing among speed, distance, time and rate.
• Perception-Reaction DistanceDistance covered during perception and reaction at a given speed. Sets where a driver could first have responded.
• Total Stopping DistancePerception-reaction distance plus braking distance — the full distance from hazard to stop.
• AASHTO Stopping Sight DistanceAASHTO stopping sight distance for a design speed and grade. Compares available sight distance against the standard.
• Time to StopTime elapsed from brake application to rest. Feeds time-space and avoidance analysis.
• Steering AvoidanceLateral distance available to steer around a hazard at speed. Tests whether an avoidance manoeuvre was possible.
• Time-Space DiagramPlots vehicle and pedestrian positions over time to show whether their paths could have conflicted.
• Acceleration from Time & DistanceAcceleration from a measured time and distance. For launch, merge and passing analysis.
• Speed from Video / Frame TimingSpeed from frame timing across a known distance. Accounts for frame rate and the uncertainty it introduces.

07–09 Energy, momentum & crush

• Kinetic EnergyKinetic energy of a vehicle at a given mass and speed.
• Speed from Kinetic EnergySpeed corresponding to a known kinetic energy. Reverses the energy calculation.
• Work Done by FrictionWork done by friction over a distance — the energy sliding removes.
• Multi-Event Energy ChainSums energy across several sequential events into one speed. For crashes with skid, impact and post-impact phases.
• Momentum, Collinear (1D)Conservation of momentum for a collinear, in-line collision.
• Momentum, 360° (2D)Conservation of momentum for angled impacts in two dimensions. The general intersection-collision solver.
• Impulse–Momentum / PDOFImpulse-momentum solution using principal direction of force, where PDOF is established from the damage.
• Three-Vehicle MomentumMomentum solved across a three-vehicle collision sequence.
• Post-Impact Speed from Final RestPost-impact speed back-calculated from final rest position. Supplies the departure speeds momentum needs.
• Crush Stiffness A, B, GCrush stiffness coefficients A, B and G derived from staged-test data.
• Crush Energy from Damage ProfileEnergy absorbed by crush from a measured damage profile. The CRASH3 crush-energy calculation.
• Delta-V from Crush EnergyDelta-V from crush energy and vehicle masses. The severity figure injury analysis turns on.
• Restitution & Delta-VApplies coefficient of restitution to refine delta-V. Matters most in low-speed impacts.
• Intrusion to Approximate ΔVApproximates delta-V from intrusion depth where a full crush profile is not available.

10–14 Specialty worksheets

• Speed from a Level Takeoff FallSpeed at a level takeoff from fall distance and drop height.
• General Vault EquationGeneral vault equation for a launch at any takeoff angle.
• Vault Plus Slide SolverCombined vault and post-landing slide, for bodies or vehicles that flew and then slid.
• Tripped Rollover / Flip SpeedSpeed required to trip a rollover, from track width and centre-of-gravity height.
• Pedestrian Throw (Searle)Pedestrian throw distance by the Searle method. Returns an upper and lower bound rather than one figure.
• Vehicle Speed from Pedestrian LaunchVehicle speed derived from a pedestrian's launch and landing positions.
• Bicycle Throw / ProjectionBicycle throw and projection distance after impact.
• Wildlife / Animal Strike ThrowAnimal-strike throw distance. Deer and livestock behave differently from pedestrians.
• Motorcycle Slide to StopMotorcycle slide-to-stop speed, with rider and machine tracked separately.
• CV Brake Force DistributionCommercial-vehicle brake force distribution across axles, for tractor-trailer braking analysis.
• Horizontal Sightline OffsetHorizontal sightline offset to a roadside obstruction — what a driver could see around it.
• Railroad Grade-Crossing SightRailroad grade-crossing sight triangle. Whether a driver could see an approaching train in time.
• Work-Zone Taper & Sight DistanceWork-zone taper length and available sight distance against MUTCD guidance.
• EDR / CDR Event SummaryOrganises EDR/CDR download data into a case summary and aligns recorded speeds with your own calculations.
• Hydroplaning SpeedHydroplaning speed from tire pressure and water depth. Establishes whether hydroplaning was possible.