The Math Behind Accident Reconstruction

Posted By: Tony Baratta | November 23rd, 2016

Does anybody fear highway driving as much as I do?  One reason I do is how regularly a driver will try to push me to go faster or pull into another lane by riding up on my tail.  And this is often when I am already driving 10 mph over the speed limit!  Perhaps it’s so scary because I know the math involved in the field of accident reconstruction.  

The events of a motor vehicle collision happen in seconds.  But in every significant motor vehicle collision involving serious injuries, hundreds of hours may be spent to evaluate exactly what occurred in those few seconds.  Lawyers dissect the facts of these few seconds and accident reconstruction experts utilize the facts developed to give opinions as to the cause of a particular accident.  The following are some basic formulas used in accident reconstruction.

Speed –    Motor vehicle travels 1.46 feet per mph.   A Vehicle traveling at 15 mph travels 21.9 feet per second.  At highway speed, 50 mph, a vehicle travels 73 feet per second.  

Perception-Reaction time –   This is the amount of time it takes a driver to detect, identify, determine a choice of action (brake, swerve, etc.).  Reaction time is typically calculated at 1.5 seconds in optimal conditions.  So, for an operator of a car driving at 50 mph, the car will travel 109 feet before a driver can even decide to brake in optimal conditions.  

Braking or stopping distance –  Of course a car does not come to a stop immediately upon braking.  The distance amount needed to safely bring a car to a stop is the sum of two distances:

  • First – the distance traveled by the vehicle from the instant the driver sights an object necessitating a stop to the instant brakes are applied

  • Second –  the distance needed to stop the vehicle from the instant of brake application.   Note: This depends upon the speed of the car and the co-efficient of friction of the roadway.  A dry roadway may have the co-efficient of friction of .60.  At 50 mph on a dry road it would take 109 feet to react and another 52 feet to safely stop.

A safe driver must maintain a distance between the front of his vehicle and the rear of the vehicle traveling ahead to stop if the vehicle ahead suddenly came to a stop.  Therefore, at 50 mph, one must maintain at least 160 feet of space, more than 1/2 a football field, between the cars to safely stop.  

An average car is 16 feet long.  That means the distance between the front of your car and the rear of another at 50 mph requires that you be 10 car lengths behind the car in front.

Travel on our roadways is heaviest at Thanksgiving.  When I think about what I am thankful for, my health and the health of my family is number one.  Please keep our roadways safe by recognizing the danger of tailgating.  

 Tony Baratta is a trial attorney in Huntingdon Valley, PA who represents clients who have been seriously injured. Tony is the founding partner of Baratta, Russell, & Baratta and a member of the Pennsylvania Brain Injury Association (BPIA). Tony is on the board for the Philadelphia VIP, a member of the Million Dollar Advocates Forum for trial attorneys and voted one of Philadelphia’s Super Lawyers for the past 10 years.

 

 

About the Author

Tony Baratta is a trial attorney in Huntingdon Valley, PA who represents clients who have been seriously injured. Tony is the founding partner of Baratta, Russell, & Baratta and a member of the Pennsylvania Brain Injury Association (BPIA). Tony is on the board for the Philadelphia VIP, member of the Million Dollar Advocates Forum for trial attorneys, voted one of Philadelphia’s Super Lawyers for the past 13 years and 2018 recipient of the First Judicial District Pro Bono Award for the Civil Trial Division.

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