Flawed premise in their research. They’re saying you can only hear motorcycles within 33ft, which is too late to react anyhow.

The times when I’ve intentionally revved my engine to get attention, it’s because a driver was about to merge into me, and they were very close. In heavy traffic I’m often feathering the clutch, and pulling it in quickly to rev is an easier reach than hitting my horn.

Anecdotally, when I switched from a small somewhat quiet bike to a full size cruiser I had WAY fewer sketchy interactions with drivers. They noticed me much better, which kept me safer. I also find loud pipes annoying, but not as annoying as people in cars killing others with the inattention.