Skidmark Analyzer for Crash Investigation at Doug's Criminal Justice Site

Skidmark Analyzer

Below is a calculator for analyzing the minimum speed of a vehicle. Simply enter the blanks and the computer will show the minimum speed of the vehicle. It is fairly self-explanatory, however there are instructions below if you need them.

OH-1 Crash Report Order Forms and OH-1 Training Slides available at ODPS

[You must download Internet Explorer 4 or Netscape 4.5 or better to view this applet]

Enter the Longest Skid of the Vehicle being used to determine the drag factor: Skip to Enter the Drag Factor if you already know it.; Place the longest skid measurement, in feet, of the test skids that you took with your police car or similar vehicle as to the one that crashed.
Enter the Speed of the Vehicle being used to determine the Drag Factor: Enter the speed of the above Test Vehicle, in miles per hour, at the time you slammed on your brakes to take the Test Skid
Compute Drag Factor: Click on the 'DragFactor' button and the Drag Factor will be shown in the entry below it.
Enter the Drag Factor: If you already know the Drag Factor, Enter it here and skip the above fields. If you need to make some kind of slope adjustment, you will have to change the number yourself.
Choose the Type of Vehicle.: Click on the type of vehicle that crashed. Either front-wheel drive, rear-wheel drive, a truck, or a motorcycle.
Enter the Skidmark Length, in feet, for Each Tire in Decimal Format: Enter skid length: 20 feet 6 inches equals 20.5, be sure the skid length is in 10ths, not inches.; 1"=.08, 2"=.16, 3"=.25, 4"=.33, 5"=.41, 6"=.5, 7"=.58, 8".66, 9"=.75, 10"=.83, 11"=.91; If you couldn't find a skidmark for a tire(s) then leave as zero. If you are computing a motorcycle, the top blank is the front tire and the bottom blank is the rear tire.
Click on Compute: The Minimum Speed at the start of the skid will be computed and will show the average length of the skidmarks and the total percentage of braking.
Enter another crash: To clear the screen and refresh the program, you may use the refresh button provided or hit your 'F5' button.

LINKS TO OTHER CRASH PAGES
Rudy Degger & Assoc.
REC-TEC
National Crash Analysis Center
Macinnis Engineering
Institute of Traffic Crash Investigators
Technical Services
TARO

The formula used to compute the drag factor is as follows: the drag factor equals the known speed of the test vehicle squared, divided by the result of the constant of thirty times the distance of the longest skid in feet. The vehicle used as the test vehicle should be a car of equal size and weight as to the car that crashed or if possible the crash vehicle itself, more often it is likely to be your police cruiser.

The formula to compute the minimum speed of the crash vehicle is as follows: The minimum speed of the test vehicle equals thirty times the distance of the average of the skid lengths, times the drag factor, times the percentage of braking efficiency, i.e., which tires left a skid. The square root of the above product is then taken to determine the mimimum speed of the crash vehicle in miles per hour when it entered the skid. The braking efficiency used is based on the Society of Automotive Engineers Technical Paper #830612 which was provided by the Ohio State Highway Patrol.