Take a look at the sentence again:
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.