Stop Saying ‘Rate Of Speed’

Stop Saying ‘Rate Of Speed’

It seems like every time a police officer describes a crash involving a car that exceeded the speed limit, he or she says the vehicle was travelling at a “high rate of speed.” This is a bad phrase and everyone needs to stop using it.

If you’re a hotshot cop standing in front of a microphone, you’ve got to speak with an air of authority, and what better way to do this than to add superfluous words to your sentences? Two such words, “rate of,” are usually thrown in when the officer really means to say “The car was travelling at a high speed.”

The reason why “rate of speed” is such a silly thing to say requires us to look at the definition of “rate,” which — and I’ll quote Merriam Webster on this — means:

a quantity, amount, or degree of something measured per unit of something else 

Speed itself is a rate — it’s defined as the rate of change of distance with respect to time. If a vehicle is travelling at 160km/h, the rate of change of its distance (in miles) with respect to time (in hours) is 100.

So to say “rate of speed” is essentially saying “rate of rate of change of distance with respect to time.” At best, this is redundant, and at worst, it’s down right wrong.

In the latter case, we know that the term “rate,” when used colloquially, often implies a rate of change with respect to time (interest rate, typing rate, etc.). So when someone says “rate of speed,” they could be saying “rate of change of speed with respect to time.” This is the definition of acceleration, which, you might recall from elementary physics, is not the same as speed, and is thus not what the officer means to communicate.

“Rate of speed” could also just be redundant, since — as mentioned earlier — speed is a rate. Maybe the officer, when using “rate of speed,” just means “the rate that is speed” (i.e. specifying to the audience that speed is a rate).

In either case, the phrase is confusing, and really doesn’t make a whole lot of sense.

So to officers (and also reporters) out there: for god’s sake, just say the damn car was travelling at a high speed. If you want to use “rate,” you can say the thing was travelling at a high rate of change of distance with respect to time.

In fact, I’d prefer that. Yes, definitely use that instead.

This article originally appeared on Jalopnik.


    • Actually this is wrong. Velocity is to displacement as speed is to distance. Velocity and displacement consider direction, speed and distance do not.

    • Actually, to be very picky, speed is the scalar quantity of velocity … velocity should always include the direction… so speed is also a term for measuring distance with respect to time, but without a particular direction.

    • Velocity is a vector and as a vector it requires a direction as well as a magnitude. Speed on the other hand is a scalar value and doesn’t require a direction so is appropriate to use. s=d/t


    • Not quite – speed is the correct term for measuring distance travelled over time. Velocity is correct for measuring displacement over time. In essence, velocity is a vector quantity whereas speed is a scalar quantity.

  • I dislike advertisements that insist promoting their product as being x times superior to the opposition. As examples:
    – A headache tablet that works 2x faster when they mean twice as fast as the opposition
    – Something that is priced 5x cheaper when they mean it’s 20% of the price of the opposition

  • This seems a misplaced objection. Rate of speed means “the rate known as speed” the same way rate of acceleration means “the rate known as acceleration”. I specialised in physics during education and never found the phrasing ambiguous.

  • I suspect this is a largely American thing: I’ve heard it while my daughter is watching YouTube car chases from the US. As Australians rotely follow US usages (elevator not lift, train station not station, etc.) it has been unconsciously adopted, and naturally, it is wrong.

  • really? you know we as humans are smart enough to do recursion right? as in when a function calls itself…

    stop splitting hairs for god’s sake !

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