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Calculation of Travel & Impact Speed

Calculation of Travel and Crash Impact Speed

  • Motorcycle Post Impact Travel Path

Pre-impact travel speed and crash impact speed are challenging to accurately estimate for vehicle operators and witnesses, so these speeds are often calculated in a crash reconstruction from both vehicle evidence and roadway evidence.

Roadway evidence are items such tire skid mark distance, gouge marks, post-impact travel distance, yaw mark geometry, vault distance and fall distance.  Special motorcycle roadway evidence can include rider vault distance, motorcycle slide distance, rider slide distance and gouge marks in the roadway indicating motorcycle lean angle.

Vehicle evidence are items such as crush damage, tire markings and  event data recorder (black box) imaging.  Special motorcycle evidence can include wheelbase change in length, handlebar damage, gear position and tire markings (front or rear).

The roadway and vehicle evidence can be analyzed together to calculate pre-impact and impact speeds in a reconstruction for a motorcycle crash or other vehicle crash.  These calculations are based upon principles such as Conservation of Momentum and Conservation of Energy.

If an analysis of a motorcycle or vehicle’s speed is desired, 830 Engineering can complete that analysis.

A simple reconstruction involves how far a vehicle will take to skid to a stop form an initial velocity as shown here:

 

How far a car will skid to a stop from different initial speeds:

Speed (mph)
f = 0.75
 f = 0.90
f = 0.30
f = 0.50
 30  40′  33′  100′  60′
 40  71′  59′  178′  107′
 50  111′  93′  278′  167′
 60  160′  133′  400′  240′
Notes: The terms used to describe the road surface (asphalt, concrete, snow, gravel) and the associated drag factors (f), are very general. They do NOT apply to all roads or crashes.