How to Calculate How Fast a Vehicle Was Traveling


The relationship between speed, distance and time is something most people learn as children. Working out how fast a vehicle was traveling is simply an applied version of this. If you know the distance traveled and the time taken, it is a simple calculation to work out the speed. If you know less information than this, however, it is still possible to use other clues to determine the speed of a vehicle.

Things You'll Need

  • Calculator (optional)
  • Find out the distance traveled. If you wish to work out how fast a plane journey was, for example, by measuring the distance between airports, it is possible to determine distance, particularly if a flight plan map is used. Similarly, by plotting a car journey on a map using a piece of string, accurate distances can be found.

  • Find out the time taken. The shorter the journey, the more important the accuracy. If the journey took several hours, calculations to the nearest 10-minute increment are usually acceptable. For shorter journeys, however, more accurate timing is needed.

  • Divide the distance traveled by the time taken. For example, if you traveled 1,500 miles in three hours, you divide 1,500 by three to work out a speed of 500 miles per hour. By adjusting the units used, different speed calculations can be found.

  • Ensure that the units are the most appropriate for the speed traveled. For example, while miles per hour is an acceptable unit for planes, for a sprinter this would be less so. To convert miles per hours into feet per second, multiply the speed in miles per hour by 1.5. A speed of 20 miles per hour is approximately 30 feet per second.

  • Use other data to calculate the speed if the distance or time is not known. A major way used to investigate crimes is braking distance. For example, according to British government figures, a car traveling at 70 mph will take 313 feet to stop. These calculations, though rough, can be used to gauge the how fast a vehicle was traveling.


  • Photo Credit Rolfo Rolf Brenner/Photodisc/Getty Images
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