Take another look at the sentence:

When Robert is riding his Honda motorcycle, he drives recklessly, weaving dangerously through rush hour traffic, Robert doesn't care that he might leave a kneecap or chunk of thigh speared on a car bumper.

The comma between motorcycle and he is completely correct. When Robert is riding his Honda motorcycle is a subordinate clause, so it cannot stand alone. He drives recklessly is a main clause. When a subordinate clause introduces a main clause, you need a comma between them.

Go back to the sentence to try again.

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