Skid Analysis

The Skid Analysis tool allows you to determine the pre and post impact speeds of a vehicle based on the length of the skid marks that you draw to mirror the real-world scene. The tool uses skid distance, drag factor (friction from different surfaces), and braking efficiency. You can analyze single and multi-surface skids.

To use the Skid Analysis tool:

1. In the diagram, draw lines that represent skid marks derived from scene data. You can change the line style to skid marks in the Line Tool Panel, but it is not required.

2. From the Power Tools ribbon, select the Skid Analysis tool.

3. If no lines are selected, the Skid Analysis window displays with no data in the table. To rename the skid set, enter a name in the Name field.

4. Select each skid mark OR select all skid mark segments in a single set that spans over multiple surfaces. This auto-populates the Skid Analysis table.

5. Configure options in the Skid Analysis Table.

6. Click OK. Repeat steps 5-9 for each row.

7. Click Report to generate a Skid Analysis report in the Print Preview window or click Close to exit the window.

Skid Analysis Table

Distance	Indicates the length of the skid. This is a calculated field.
Drag	Select the type of terrain and enter a friction value in the Friction dialog. Select Change All to use the same surface for all skids in the set. Enter a value or select a surface for an approximate value, and then click OK.
Braking	Configure settings in the Braking dialog.Braking Value Enter the values for each tire. The overall lengths of each skid are not averaged. Enter the correct braking percentage to maintain accuracy. If all four wheels are braking evenly, there will be four distinct marks, and braking efficiency is 100% or 1. Front Wheel Drive Enter the appropriate options for front wheel drive vehicles. This is typically 70% front, 30% rear. Rear Wheel Drive Enter the appropriate options for rear wheel drive vehicles. This is typically 60% front, 40% rear. Tires Select both left or both right tires (regardless of drive type) and each wheel defaults to 50%. Select two from the front or rear, the setting will be between 40%, 60% 70%, and 30%, depending on the selected drive type.
Percent Grade	Uphill skids display as positive percentages; downhill skids display as negative values. This is a calculated field.
-WB	If you are unsure if the skids are from the front or rear tires, deduct the wheelbase to yield a lower speed by selecting WB field.Enter the wheelbase length in the Wheelbase field located on the right of the Skid Analysis dialog. Only deduct wheelbase on pre-impact skids or skids from a vehicle that slides to a stop when impacting another object.DO NOT apply Wheelbase Deduction to post-impact skids.Subtract wheelbase from only one set of skid lines, and only one surface when they pass over multiple surfaces.

Skid Analysis Formulas

Skid analysis uses three formulas to make calculations.