Robert T. Lynch, PE, Sr. Collision Reconstruction Engineer ::::
We’ve all experienced it – you’re driving on the highway minding your own business, when a vehicle surprises you as it suddenly passes you at a high speed. Your first reaction (after your heart stops racing from the initial shock) is to look to see if there is a police officer around to pull the driver over for speeding. Your second thought is… wondering just how fast the vehicle was going. Well, wonder no more. I’m going to outline a simple approach for you, rooted in basic physics, that allows you to reasonably estimate the speed of the vehicle. I know some of you get apprehensive when you read the word “physics,” but don’t be afraid, as this process works for even the non-engineer.
Here’s what you do… as soon as the vehicle passes your vehicle, start counting to 10, as if you’re playing hide-and-go-seek, counting the numbers out as seconds. When you get to 10, note the location of the speeding vehicle ahead of you. Roadside poles or painted white dashed lines on the roadway provide good visual cues in order to determine how far ahead the speeding vehicle has traveled in the 10 seconds since it passed you. We’ll call this the “10-second location.” Now, without stopping your rhythm of counting, continue on to 11… 12… 13 seconds… until your vehicle has now reached the same location where the speeding vehicle was after 10 seconds. If it takes you 13 seconds to cover the same distance that it took the speeding vehicle to cover in 10 seconds, the speeding vehicle is going approximately 30% faster than you; 14 seconds equates to 40% faster and 15 seconds equates to 50% faster. As an example, if you are traveling at 60 miles per hour and you count to 14 seconds when you reach the “10-second location,” the speeding vehicle was traveling 40% faster, or at a speed of approximately 84 miles per hour!
This approach only works if your speed remains relatively constant, so no sudden acceleration or braking while counting. It should also be noted that the counting should technically start at 0, and not at 1, but unless you observe the vehicle approaching in your rearview mirror (or hear the vehicle approaching) and are aware of the vehicle before it passes you, starting the counting at 1 is reasonable to account for your reaction time to the sudden and unexpected appearance of the vehicle as it passes you. For those of you who are not good at counting seconds in your head, counting along to the beats of a song playing on the radio will yield the same results.
Try it out the next time you’re on the open highway and you’ll be hooked. You’ll never go back to “wondering” how fast the vehicle sped by, but instead have a scientific approach to “knowing” just how fast the vehicle was going.
Disclaimer: No, I do not own a Maserati. I’m just a Joe Walsh fan (… and also an E-A-G-L-E-S Eagles! fan).
“Life’s been good to me so far.”
Robert T. Lynch, PE is a Sr. Collision Reconstruction Engineer with DJS Associates and can be reached via email at experts@forensicDJS.com or via phone at 215-659-2010.