at speeds of/at a speed of

[diamondcutter]

An elite sprinter can run at about 40 kilometers per hour, while the fastest dog, the greyhound can race at speeds of 60 kilometers per hour. Some horses can gallop at about 80 kilometers per hour, and antelopes can run close to 95 kilometers per hour.

(Reading Tracks 2, International Language Teaching Services Ltd)

In the 1st sentence, I wonder why the writer says “at speeds of 60 kilometers per hour” not “at a speed of 60 kilometers per hour”.

[Piscean]

The writer was perhaps conflating the ideas of 'at a speed of 60 kilometres per hour' and 'at speeds of up to 60 kilometres per hour'.

[PeterCW]

To a native speaker it doesn't feel unnatural but, as an editor, I would be inclined to "correct" it in the way that you suggest.

[Tarheel]

An elite sprinter can run at about 40 kilometers per hour, while the fastest dog, the greyhound can race at speeds of 60 kilometers per hour. Some horses can gallop at about 80 kilometers per hour, and antelopes can run close to 95 kilometers per hour.

(Reading Tracks 2, International Language Teaching Services Ltd)

In the 1st sentence, I wonder why the writer says “at speeds of 60 kilometers per hour” not “at a speed of 60 kilometers per hour”.

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