Vehicle Speed Calculator

This calculator is used to determine the speed of a vehicle when the roadway friction, roadway slope and skid distance are known. The friction table below can be used to approximate the roadway friction based upon different roadway surface types and whether or not the surface is wet or dry.

  Roadway Friction: Example: 0.60  
  Roadway Slope: % Use 0% slope for flat roadway. Use negative sign ( - ) for downhill grade. Example: 2.5 for uphill grade and -2.5 for downhill grade.  
  Distance of Skid Mark: ft Example: 100  
  This calculator utilizes the following equation: V = √(30*D*F)  





V = Speed of Vehicle (mph)

D = Distance of Skid Mark (feet)

F = Adjusted Friction = μ ± G where μ is the coefficient of friction and G is the grade of the roadway.

friction coefficients table image

This calculator does not account for speed loss due to an impact with another object, hydroplaning conditions, tractor / trailers, and should not be used for vehicles traveling over multiple types of surfaces (ie. traveling over asphalt, concrete, gravel during one skid).

Atlanta Engineering Services, Inc. does not assume any liability for any errors in this calculator. This tool shall not be used for any insurance or litigation purposes. Atlanta Engineering Services, Inc. recommends that a licensed professional engineer specializing in traffic accident reconstruction be consulted for these types of situations.

Related Information about Traffic Accident Reconstruction

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The accident scene investigation 

Atlanta Engineering Services, Inc. offers scene mapping... read more here

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View a sample engineering report here

Why you need an expert witness

Calculating the stopping distance

Multiple surfaces calculator to determine the stopping distance when there is more to consider.

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Reconstructing accidents involving Non-Commercial trucks

Read how vehicle defects can be the cause of a traffic accident here. 

It just may be those roadway ruts that caused you to hydroplane, find out more here

Was it poor design or layout that caused the accident?

See real 3D accident simulations with this link

More 3D accident reconstruction videos can be found here

See actual photos of traffic accidents here

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