Vehicle Speed Calculator over Multiple Surfaces and then Impacts

This calculator is used to calculate the speed of a vehicle traveling over one or more surface types and considers an impact with another vehicle or object.

This calculator can be used if there aren't multiple roadway surface types or an impact. In this situation, just leave the extra input fields empty.

    Surface 1 Surface 2 Surface 3 Impact  
  Roadway Friction:    
  Roadway Slope: % % %    
  Distance of Skid Mark: ft ft ft    
  Speed Loss Due to Impact:       mph  

When inputting roadway slope data above: Use 0% slope for flat roadway. Use negative sign ( - ) for downhill grade. Example: 2.5 for uphill grade and -2.5 for downhill grade.

  Calculator uses the combined speed formula:

Sc = √(S12 + S22 + S32 + SImpact2)









S1 = Speed Loss Accross Surface 1 (mph) = √30*D1*F1

S2 = Speed Loss Accross Surface 2 (mph) = √30*D2*F2

S3 = Speed Loss Accross Surface 3 (mph) = √30*D3*F3

SImpact = Speed Loss Due to Impact (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.


The friction table below can approximate the roadway friction based upon different roadway surface types and whether the surface is wet or dry.

This calculator does not account for hydroplaning conditions and tractor / trailers.

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

Types of traffic accidents

Collision analysis in 10 steps

The accident scene investigation 

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

Learn how a vehicle black box and it's downloads can prove up evidence

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.

Vehicle speed calculator

Animation expert

Accidents involving motorcycles

How a vehicle inspection analysis can help you after an accident

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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